Connecting IDE Drives
Contents
1. After reset the drive defaults to read ahead feature enabled Whew this was a lot of stuff I hope it was not too hard However now you should know about IDE commands in detail if you didn t fall asleep while reading Before we start practical work here for the programmers are the short form tables that 1 promised 13 13 Overview Table 1 Task File Registers as printed in part II cso CS1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 A2 Al AO Addr 0 0 0 1F0 0 0 1 1F1 0 1 0 1F2 0 1 1 1F3 1 0 0 1F4 1 0 1 1F5 1 1 0 1F6 1 1 1 1F7 1 1 0 3F6 1 1 1 3F7 Table 2 Error Register Y e OrRrFNWHROAN Flag BBK UNC IDNF ABRT TKO Meaning Bad block mark detected Uncorrectable data error Sector ID not found Read Function Data Register Error Register Sector Count Sector Number Cylinder Low Cylinder High SDH Register Status Register Alternate Status Drive Address Write Function Data Register Write Precomp Reg Sector Count Sector Number Cylinder Low Cylinder High SDH Register Command Register Digital Output Not Used Command aborted status error or invalid command Track 0 not found during recalibration Table 3 SDH Register Bit 7 6 5 4 3 0 Flag EXT SIZE DRV HEAD Meaning Extension Bit Always 1 Sector Size Always 01 512 byte sectors Drive bit Master single drive 0 slave 1 Head field Binary head number 0 15 Table 4 Status Register Alternat2. as I know most IDE drives follow the data field description above However there still are many things which are manufacturer dependent Fortunately these details are not critical To give you some examples The controller model field of Conner drives contains plain text with the complete drive description like Conner Peripherals 40 MB CP3044 Seagate s IDE drives offer only a short cryptic ID string which sometimes doesn t even contain the drive type A very interesting difference even between drives of the same manufacturer shows up with the Number of cylinders heads sectors fields Some drives show their physical values there independent of the active emulation mode for example my CP 3044 does so Other drives always show the parameters of the active emulation or those of the default emulation mode Surprising especially with my drive is that the physical parameters can t be used for drive operation As a result the data delivered by this command must be considered carefully However it s normally possible to extract useful information by reading the drive s ID information for several different active emulation modes 12 2 Read Write Sector Buffer E4h E8h These are the last two common IDE commands With these commands it s possible to read or write the drive s sector buffer directly I haven t found any use for these yet but probably there is at least was one In my opinion these commands are useless for n
3. covered most of the manufacturer independent commands in the previous part However there are three commands not explained yet Let s get started with the command which was already used in the sample program printed with the previous part so you ll now know what you really did there in case you ran that program 12 1 Identify Drive ECh This command reads some detailed parameter information from the IDE drive Again it s invalid for the older external controllers It is started by writing the command code into the command register and then it exe cutes like a Read Sectors command The DRQ Flag will be set declaring that data can be read After having read a complete sector 256 words 512 bytes of data the DRQ flag will be reset and the drive will be ready again The data consists of the following fields Word Adr Byte Adr Type Content 0 0 word Configuration ID word 1 2 word Number of fixed cylinders 2 4 word No of removable cylinders 3 6 word No of heads 4 8 word No of unformatted bytes per physical track 5 10 word No of unformatted bytes per sector 6 12 word No of phyical sectors per Tracks 7 14 word No of bytes in the inter sector gaps 8 16 word No of bytes in the sync fields 9 18 word 0 10 19 20 39 20 char Serial number 20 40 word Controller type 21 42 word Controller buffer size in sectors 22 44 word No of ECC bytes on long commands 23 26 46 53 8 char Controller firmware revision 27
4. format any track Modern drives are hard sectored by the manufacturer with the sector size unchangeable by the user But by virtually formatting a track one can assign new sector numbers for example starting with 0 instead of 1 However the sector numbering order is often ignored Because IDE drives commonly have built in cache memories the definition of an interleave factor would make no sense So the drive always uses the fixed sector ordering which gives maximum performance in combination with the cache To make things still more complicated the Format Track command of IDE drives allows for the assignment of data sectors to the spare sectors and for the release of those assignments look at the descriptor bytes above All IDE drives have some spare sectors to which the data of defective sectors is automatically mapped Normally there is one spare sector per track resulting in about 2 3 spare capacity This is more than enough When a sector appears too unreliable during normal operation the drive simply marks that sector as bad internally and moves the data to the nearest free spare sector As long as not all spare sectors are assigned the user won t notice anything However these assignments can also be done explicitly by use of the Format Track command But it is strongly recommended not to do that First one will normally get no defect list for an individual IDE drive containing the BFI positions Second even if a sector which
5. the data of the starting sector is read into the sector buffer and the DRQ data request bit in the status register is then set This informs the host that the sector data can be read from the sector buffer When this is completed DRQ is reset and the drive is ready again For reading multiple sectors SC gt 1 when the sector buffer is completely read and DRQ is reset the busy flag is set again immediately and the next sector s data is read into the sector buffer When DRQ is set again the next sector s data can be read from the buffer This is repeated until the SC register value reaches zero this register is decremented with every successfully read sector In any case after successful completion of this command the SC register contains a zero value and the other registers in the task file are updated to contain the cylinder head and sector number of the last read sector If an error occurs the task file will contain the parameters of the sector at which the error was detected For the Read Sectors command two options are possible The M option is valid only with the original WD1010 controller thus with old AT s When M was not set 0 the SC content was ignored and exactly one sector was read When M was set 1 the SC value was taken as the count of sectors to read Today things are different With modern IDE drives if the M bit is set an error occurs So this bit must always be cleared The other option L is val
6. was assigned to one of the spares is marked good again the related spare sector can not be used again So with every unassignment of a spare sector you loose that irretrievably So we come to this result with standard i e ST 506 drives and external controller i e WD1010 it makes sense to format the drive in order to freshen the surface magnetism to get a defined state sector numbering and order and to mark defect sectors as bad so that the operating system can behave accordingly With IDE drives it s best to leave them just as they are coming from the factory 9 6 Seek 7xh This command is used to move the r w heads to a particular cylinder explicitly For normal operation of the drive it is usually not necessary since all r w commands perform implied seeks However this command can easily be used for benchmarks to determine the drive s seek times With the WD1010 controller the four lower bits of the command byte contain the step rate described above IDE drives simply ignore these four bits 9 7 Execute Diagnostics 90h This command is common to all IDE drives but not available with the WD1010 controller When issued the drive performs an internal self test If the drive is a master drive and a slave drive is connected to it the master also waits a limited time for the slave to complete its self test During all this time it is busy the according flag in the status register is set After finishing the test proced
7. 46 54 93 40 char Model number 47 94 word No of sectors interrupt 0 no support 48 96 word Double word transfer flag 1 capable 49 98 word Write protected 50 255 100 511 reserved read as zero values Some of these fields have special meanings The configuration ID word consists of 16 single bit flags However I don t know for sure if their meaning is really manufacturer independent The controller type word is encoded as a number representing a particular type 11 Configuration ID word bit flags 15 Non magnetic drive 14 Format speed tolerance gap required 13 Track offset option available 12 Data strobe offset option available 11 Rotational frequency tolerance gt 0 5 10 Data transfer rate gt 10 MB s Data transfer rate gt 5 MB s lt 10 MB s Data transfer rate lt 5 MB s Removable disk Non removable disk Spindle motor can be switched off Head switching time gt 15 us Not MFM encoded Soft sectored Hard sectored reserved PNW BB OUD N OO o Controller type word values Not specified Single ported single sector buffer Dual ported multiple sector buffer 3 2 with look ahead read capabilities yeo The string type data fields character arrays contain plain text information about the serial number controller model and firmware revision of the drive Each word holds two characters which must be displayed with the high byte character first in order to get readable results As far
8. C D H CD D SC C D H sc sc SC When an error occurs the error flag in the status register ERR is always set For the different groups of commands the following status error flags are valid then Recalibrate Read Verify Read Long Write Write Long Format Seek Diagnostics Initialize R W Buffer Identify Set Cache Invalid command Table 9 Interrupt Conditions ABRT TK0 DRDY DWF DSC BBK UNC IDNF ABRT DRDY DWF DSC CORR BBK IDNF ABRT DRDY DWF DSC IDNF ABRT DRDY DWF DSC ABRT ABRT The drive generates an interrupt if enabled under the following conditions Recalibrate Read Write Verify Format Track Seek Initialize Power Commands except Sleep Set Sleep Mode Read Buffer Identify 14 Example Program after successfully reaching track 0 each time DRQ is set when DRQ is set from second sector on only when multiple sectors are written after completion for all sectors after completion after command is issued initiated when drive is in sleep mode when data is ready for reading Now let s come to the example routines for accessing an IDE drive These examples are given as Turbo Pascal 3 0 source based on my IDE test program They apply to the use of my IDE interface board described in TCJ 56 so there always are 512 data bytes transferred instead of 256 data words In all examples named constants are used for accessing the IDE registers at their particular I O addresses These nam
9. Connecting IDE Drives by Tilmann Reh Contents 1 Foreword 2 Remembering the Basics 3 The IDE Interface 4 Now Let s Go Into Details 5 IDE Interface Registers 6 Last Words 7 Terminology 8 Register Accessing 9 The Commands 9 1 Recalibrate Ixh a el SB ee ES 9 2 Read Sectors 2 te ese ae see Bs ee ee a pta a a e 9 3 Write Seetors 3xh um a A rennen a a a ety Geese 4 9 4 Scan ID Verify Sectors 4xh 2 2222 ooo 9 5 Format Track 58h oeaan nr A Soe ro A tee Br io A A AE A a ne ae long Go amp Sp 9 7 Execute Diagnostics 90h ee eee 9 8 Set Drive Parameters 91h 2 ee 10 The break a sample program 11 I must apologize 12 Commands Continued 12 1 Identify Drive ECH v2 22a AR LINIE ieee eos 12 2 Read Write Sector Buffer E4h E8h 2 2 2 nn 12 3 Block Mode Commands Read Write Set Multiple CA C6h o o o o 12 4 Power Commands E0 E6h except E4h o oo e 13 Overview 14 Example Program 14 1 General access Wait for drive ready wait for data request o o o e 14 2 General access Command issue or 14 3 General access Reading Writing the sector buffer o o o e e 14 4 General access First access initialization o 14 5 Data access Single sector read e 14 6 Data access Single sector write ee ee 1 Foreword This text has been published i
10. Number 0 1 1 0 0 1F4 Cylinder Low Cylinder Low 0 1 1 0 1 1F5 Cylinder High Cylinder High 0 1 1 1 0 1F6 SDH Register SDH Register 0 1 1 1 1 1F7 Status Register Command Register 1 0 1 1 0 3F6 Alternate Status Digital Output 1 0 1 1 1 3F7 Drive Address Not Used The above addresses are those used in the PC AT Of course they are dependent on the decoding of the chip select signals The registers accessed via CS1 might differ depending on the manufacturer of the drive As far as I know they don t always follow the compatibility principle with the first hard disk controller of the PC AT The registers being accessed with CS0 are also called the Task File so sometimes the IDE is also referenced to as Task File Interface The error register can only be read It contains valid information only if the error bit in the status register is set Only five of the eight bits are used They have the following meaning Bit 7 Bad block This bit is set when the requested sector s ID contained a bad block mark can be set when formatting the disk Bit 6 Uncorrectable data error Set when the sector data can t be recreated even with ECC Bit 4 Requested sector ID not found wrong sector number Bit 2 Command was aborted due to drive status error or invalid command Bit 1 Track 0 has not been found when recalibrating The unused bits are always read as zero However I guess it s best not to rely on that The write precompensat
11. ain So Pll make a break here and continue the command descriptions in Part IV of the Connecting IDE Drives article series Instead Pll show you a short program which reads the ID information of an IDE drive within a PC AT This sample program was written with Turbo Pascal 5 5 but may easily be used with any version above 4 0 You can try out this program on your AT if you have one with an IDE drive and play with it until receiving the next issue of TCJ with Part IV of the article That part will finish the command descriptions and will also contain some more programming examples and shortform tables as a programmer s overview of the IDE interface definition 10 Abbreviation list BFI Byte From Index position of surface defect DRQ commonly used for Data Request bit flag or signal line IDE Integrated Drive Electronics hard disk interface type I O Input Output PC AT Personal Computer Advanced Technology computer class r w read write ST 506 older hard disk interface standard used between separate controllers and MFM RLL drives 11 I must apologize Sorry for the badly formatted Pascal listing printed with part III in the previous issue of TCJ Bill had to delete all the empty lines in order to compress it to a single page Now I know that this doesn t make a program more readable or easier to understand even if it s written in Pascal We will try to do this better in the future 12 Commands Continued We already
12. ations AT Advanced Technology Class of PC s BIOS Basic I O System Hardware dependent part of OS CMOS Complementary Metal Oxid Silicon Semiconductor technology CRC Cyclic Redundancy Check Error detection code see also ECC ECB 22 European standard 8 bit system bus ECC Error Correction Code Additional data for security IDE Integrated Drive Electronics Intelligent hard disk interface IEEE Institute of Electrical and Electronics Engineers 1 O Input Output self explanatory ISA Industry Standard Architecture PC AT expansion bus LED Light Emmitting Diode Optoelectronical component OS Operating System Software which makes computers usable PC Personal Computer Synonym for the worst computer architecture TTL Transistor Transistor Logic Digital component standard 74xx series XT eXtended Technology Class of PCs previous to AT ZBR Zone Bit Recording Variable Density Recording Method 7 Terminology Using common terminology I often simply refer to the drive when in fact I am thinking of the integrated controller of an IDE drive However when explicitly talking of an external controller like the WD1010 I always refer to the controller 8 Register Accessing Let us first recall the Task File It consists of the data register a set of six parameter registers and the com mand status register For those who don t have Part II lying nearby here is a shortform Relative Address Register Abbr 0 Data Register D 1 Error R
13. dependent sources However there still might be some slightly different drives or controllers out there Please inform me if you encounter problems or differences with your disk One general feature of both the WD1010 controller and modern IDE drives is implied seeks That means you don t have to explicitly move the read write r w heads to the desired cylinder before starting to read from or write to the disk When the command is issued and the actual cylinder number doesn t match that of the cylinder registers an implied seek is performed transparent to the user This applies to every command where it may be needed Read Write Verify Format 9 1 Recalibrate 1xh This command moves the r w heads of the selected drive from anywhere to cylinder 0 The controller waits for the drive to complete the seek before the task file is updated and the busy flag is reset Upon successful completion of the command the error register and the cylinder registers are set to zero while SC SN and SDH remain unchanged 9 2 Read Sectors 2xh This is probably the mostly used command It will read from 1 to 256 sectors of disk data as specified in the SC register with an SC value of 0 meaning 256 sectors to be read The starting sector is defined by SN C and H in the task file When the task file contains invalid parameters an error occurs Otherwise the r w heads are moved to the requested cylinder if they are not already there implied seek Then
14. e Status Register Flag BSY DRDY DWF DSC DRQ CORR IDX ERR Meaning Drive busy Task file cannot be accessed Drive ready up to speed and ready for command Drive write fault Drive seek complete actuator on track Data request ready for data transfer Corrected data bit is set when data has been recovered by use of ECC Index Active once per disk revolution Error See other bits and error register Table 5 Digital Output Register Bit 2 1 Flag Meaning SRST Software reset active when set to 1 Interrupt enable active when set to 0 IEN Table 6 Drive Address Register Bit 7 6 5 2 1 0 Flag WTG HSx DS1 DSO Meaning not driven for PC floppy compatibility Write gate active when 0 Head select 3 0 one s complement of active head Drive 1 selected active when 0 Drive 0 selected active when 0 14 Table 7 Commonly needed Commands with Parameters Code Command Parameters 1x Recalibrate 20 Read Sectors with retry 30 Write Sectors with retry 40 Verify Sectors with retry 50 Format Track 7x Seek 90 Exec Diagnostics 91 Set Drive Parameters Ex Power Commands see below E4 Read Sector Buffer E8 Write Sector Buffer EC Identify Drive EF Cache On Off Power Commands EO Standby Mode El Idle Mode E2 Standby Mode with APD E3 Idle Mode with APD E5 Read Power Mode E6 Sleep Mode Table 8 Error Conditions D SC SN C D H SC SN C D H SC SN C D H
15. ed constants must be declared elsewhere Their names are derived from the related IDE register names and IDE commands The examples are programmed in a very modular fashion so that they are easy to understand For implemen tation in a system BIOS for example most of the subroutines will contain so little code that the complete read write routines will normally be coded inline In addition a real implementation unlike these examples 15 will have time out functions in most loops If someone is interested in the IDE driver of my CPU280 system BIOS please contact me however note it s Z280 assembly language and commented in German 14 1 General access Wait for drive ready wait for data request In Pascal two small procedures serve this purpose In assembly language I use two macros instead because the subroutine calling overhead would be too much procedure Wait_Ready begin repeat until port IDE_CmdStat lt 128 end procedure Wait_DRQ begin repeat until port IDE_CmdStat and 8 lt gt 0 end 14 2 General access Command issue procedure IDE_Command Cmd byte begin Wait_Ready port IDE_CmdStat Cmd end 14 3 General access Reading Writing the sector buffer In the Pascal implementation the two functions return a Boolean value which is true if there were no errors during r w of the buffer Both routines require the drive to be ready for data transfer function Read_SecBuf var Buf BufType boolean
16. eg Write Precomp Reg E WP 2 Sector Count SC 3 Sector Number SN 4 Cylinder Low C 5 Cylinder High C 6 SDH Sector Size Drive Head D H 7 Status Reg Command Reg Also remember that the data register is the only 16 bit register Every parameter register of the task file is freely accessible as long as there is no active command Before loading the command register all related parameter registers must contain the appropriate values They may be loaded in any order After the command register is loaded the issued command is immediately started The original WD1010 hard disk controller chip had a flag bit 1 of the status register which was set during execution With IDE drives the BUSY flag of the status register is simply set until the command execution is completed The WD1010 controller chip knew only 6 commands However some of the commands have option flags within them To support additional features today s drives have many more commands The following is a list of common commands options and needed parameters with the WD1010 commands marked by an asterisk and the manufacturer dependent expansions marked with a plus sign Command Type 7 6 5 4 3 2 1 0 Hex Parameters Recalibrate 0 0 0 1 Rate 10 1F D Read Sector s 0 0 1 0 0 M L T 20 27 SC SN C D H Write Sector a 0 0 1 1 0 M L T 30 37 SC SN C D H Scan ID Verify x 0 1 0 0 0 0 0 T 404 D SC SN C H Write Format 7 0 1 0 1 0 0 0 0 50 C D H SC SN Seek E 0 1 1 1 Ra
17. g in the order they are stored in the buffer So it is possible to define an interleave factor by appropriate physical sector numbering Here is an example Addr 00 00 01 00 11 00 02 00 12 08 00 03 00 13 00 04 00 14 10 80 05 00 15 00 06 00 16 etc Here we see the first 12 of 32 ID words The starting sector has number 1 as usual The interleave factor is two since each sector appears two sectors after its logical predecessor You can also see that sector number 5 the 9th sector physically is marked bad Due to surface errors on the hard disk there are some positions where the media won t store magnetic informa tion reliably enough if at all The defect list for a particular drive then shows the cylinder head and BFI byte from index value of the defect People then had to calculate the bad sector position and number from each of those BFI values However it is not commonly known that the relationship between the BFI value and the sector number depends not only on the sector size but also on the interleave factor and the starting sector number Again things changed as the years went by I already mentioned when introducing the features of modern IDE hard disks that those drives don t have defect lists any more due to the usage of internal spare sectors For compatibility reasons these drives still accept the Format Track command However most drives only simulate its execution internally they don t really
18. gister contents is smaller than 12 With a maximum value of 220 the maximum delay is about 18 minutes These limits again apply to my particular drive other drives may have other specifications 12 4 3 Read Power Mode E5h This command reads the actual mode If the motor is spinning meaning that the drive is in idle mode the value FFh will be returned in the SC register Else when in standby mode or just spinning up a zero value will be placed in the SC register 12 4 4 Set Sleep Mode E6h This command puts the drive into sleep mode immediately Every internal activity is terminated and all circuitry switched off There are some more power related commands having the command codes F8 FDh except FCh Their general meaning is similar to the power commands described above E0 E5h except that the time delays are specified more exactly in counts of 0 1 seconds However I have not yet seen a drive which supported these commands and I don t have detailed information about them 12 5 Cache On Off EFh This is the last command which I will explain here It is used for enabling or disabling the automatic read ahead feature read cache of the drive The write precompensation register WP is mis used as a parameter register for this command today this is the only use of the WP register If the WP register contains AAh the feature is enabled with 55h it is disabled Every other value will result in an aborted command error
19. id only with modern IDE drives L stands for long and means that the additional ECC data which the drive automatically puts after each sector is transferred after the net data of each sector When this option is set the drive also does not check these ECC bytes so it won t detect or correct errors This provides a way to read a sector s remaining data even if it is nonrecoverably damaged When using this option remember that the ECC data is transferred as bytes through the word wide data register 9 3 Write Sectors 3xh The Write Sectors command is very similar to the Read Sectors command Of course the data flow direction is different This command will write up to 256 sectors of data to the disk All parameters and options are similar to those of the Read Sectors command After writing the command to the command register the drive sets the DRQ flag informing the host that the data can be written into the sector buffer When all data has been transferred DRQ is reset and the drive starts writing the data buffer contents to the disk The busy flag is set as long as the drive is physically writing to disk The SC register is decremented and if not zero thereafter DRQ is set again for the next sector When using this command with the L option the drive will use the ECC bytes delivered by the host and not generate any by itself For the M option the details described above apply 9 4 Scan ID Verify Sectors 4xh Th
20. ining two IDE drives master slave It normally can also be left open The data bus carries the 16 bit data words to and from the host However when accessing the control and status registers of the IDE drives only data bits 0 through 7 are used 8 bit transfer The data bus lines are tri state lines that may be connected directly to the host s data bus However to meet the host bus specs and to avoid noise problems caused by the interface cable a bus driver IC should be used to decouple the IDE bus and the host bus The drive is accessed using the selection signals CSO and CS1 This also has historical compatibility reasons Together with the three address lines there could be two times eight addresses being occupied by an IDE drive However while the main register set really has eight registers and is accessed with CSO active the other set with CS1 has only two valid addresses We will have a deeper look at all the registers later The data transfer is always strobed by the timing signals IORD and IOWR for reading and writing respectively The address strobe ALE is often unused in the drive it should be pulled high for static address lines non multiplexed busses The status signals are not absolutely needed to use IDE drives Some of these signals are not commonly delivered at all for example IOCHRDY I O Channel Ready which is a WAIT signal for the host when the drive is much slower than the host processor in terms of in
21. ion register was previously used to set the starting cylinder for write precompensation a slight shift of the serial data stream pulses to compensate for some magnetic effects on the disk surface Since IDE drives handle all that internally this function is not needed any more Today this register is often used as a parameter register for enabling or disabling look ahead reading We ll have a deeper look at that when talking about the various commands of IDE drives The sector count register defines the number of sectors to be read or written with the next read write command A zero value causes 256 sectors to be processed so the count varies from 1 to 256 This register is also used during drive initialization to specify the number of sectors per track remember the emulation capability The sector number register contains the starting sector number for any disk access After a sector is processed and after the command is completed this register is updated When an error occurs this register contains the ID number of the erroneous sector Normally the sector numbers start with 1 and increase with each sector However by reformatting the disk this order and the values may be changed The cylinder low and cylinder high registers contain the 10 bit cylinder number to be accessed Since many drives have more than 1024 cylinders today the cylinder high register is often expanded to more than two bits Like the sector number register these registe
22. is flag is set the task file registers must not be accessed due to internal operations Bit 6 Drive ready This bit is set when the drive is up to speed and ready to accept a command When there is an error this bit is not updated until the next read of the status register so it can be used to determine the cause of the error Bit 5 Drive write fault Similar to drive ready this bit is not updated after an error Bit 4 Drive seek complete This bit is set when the actuator of the drive s head is on track This bit also is updated similarly to drive ready Bit 3 Data request This bit indicates that the drive is ready for a data transfer Bit 2 Corrected data flag Set when there was a correctable data error and the data has been corrected Bit 1 Index This bit is active once per disk revolution May be used to determine rotational speed Bit 0 Error flag This bit is set whenever an error occurs The other bits in the status register and the bits in the error register will then contain further information about the cause of the error The command register is used to pass commands to the drive There are many commands not always using all parameters in the task file Command execution begins immediately after the command is written to this register Since this article is already quite long 1 will cover the commands their parameters and their usage in another article probably in the next TCJ issue The alternate status regis
23. is is a very strange command As far as I know it is the only one that is totally incompatible between the old AT s hard disk controller and today s IDE drives It would appear that this command was never used by common system implementation or application software For the WD1010 controller this is the Scan ID command It takes no parameters at all except for the drive and head which originally had to be contained in a register external to the WD1010 When the command is started the controller searches for the next ID field and reads the contents into the task file This way the actual drive head cylinder and sector size could be examined The sector number was also transferred into the task file so the sector numbering order could be figured out by repeating this command fast enough For the IDE drives this is a completely different command Verify Sectors It is similar to the Read Sectors command except that no data is transferred to the host and the L option is not supported Thus it needs all parameters in the task file Up to 256 sectors of data will be read into the sector buffer and their ECC bytes will be verified The DRQ flag will never be set The completion status of the command can be read from the status register It is interesting that both types of controller drive support the retry option so this is the only compatibility of this command 9 5 Format Track 5xh Originally this command was used to physicall
24. n TCJ several years ago in three parts For your convenience I concatenated them into one file again Sometimes the text refers to other articles in TCJ especially to a description of my ECB bus based IDE interface However I think the information in this text contains all necessary information about IDE interfacing in general 29 October 2001 Tilmann Reh 2 Remembering the Basics Let us first have a short look at the drives we want to use When discussing the different hard disk interfaces in my last article I already pointed out that IDE drives of the AT type thus often called AT bus drives Bill Kibler calls them ATA drives but this abbreviation is not the usual one at least in Europe are the ones with the best price performance ratio one can get This is even more the case now So IDE drives still are the very first choice if you are looking for a good and cheap hard disk for your computer But what s special with those drives I already mentioned that the IDE drive contains the complete hard disk controller It is accessed with a system bus interface compatible with the PC AT ISA bus and offers control and data registers still compatible with the very first PC AT hard disk controller based on the WD 1010 controller chip But even if those specifications come from something I don t like at all why not use the low price components for real computing i e with a CPU280 Bringing the hard disk controller into the drive electronics
25. ne cable The second drive slave is then chained to the first one master However I heard about problems when trying to connect different drives from different manufacturers And the capacities of today s drive are so high that a single drive will always be enough for an 8 bit personal computer system So I never tried this option To understand the interface in detail let s have a closer look at the IDE interface connector and its signals 1 RES 2 GND 3 D7 4 D8 5 D6 6 D9 7 D5 8 Di 9 Du 10 D11 11 D3 12 D12 13 D2 14 D13 15 D1 16 D14 17 DO 18 D15 19 GND 20 No Pin 21 IOCHRDY 22 GND 23 IOWR 24 GND 25 IORD 26 GND 27 IOCHRDY 28 ALE 29 No Connection 30 GND 31 IRQ 32 1016 33 Al 34 PDIAG 35 A0 36 A2 37 CS0 38 CS1 39 ACT 40 GND The signals of the IDE interface can be collected in several groups The general control signals are RES Reset and PDIAG Passed Diagnostics The data bus consists of 16 data lines D0 D15 The access control lines are three address lines A0 A2 the select signals CSO and CS1 Chip Select 0 1 and the strobe signals IORD and IOWR and eventually ALE the address strobe The remaining signals IOCHRDY IRQ ACT 1016 are status signals 4 Now Let s Go Into Details The reset signal normally is active low However I heard about drives with an active high reset signal but I never saw one or read such specifications The PDIAG pin carries a bidirectional signal used for cha
26. number of sectors per track cylinders and heads Because of the differences it is advisable to first collect detailed information about the supported emulation modes of a particular drive before defining its operating parameters Normally it s best to operate a drive in its native mode so the logical parameters equal the physical ones However there s another strange detail there are drives which don t support the native mode My Conner drive again serves as example the drive has 1053x2x40 sectors cylinders by heads by sectors physically but supports only a pseudo native mode with 526x4x40 sectors and an emulation mode with 981x5x17 sectors which is for compatibility with older 40 MB drives Additionally depending on the internal software version the drive defaults to the emulation mode or to the pseudo native mode As a result it is recommended that the operating parameters always be defined after power up or reset And to define them you must have detailed information about the drive you want to use There is a Product Manual for every drive type describing all those details Unfortunately these manuals are hard to get Most dealers are not willing to give them to their customers and some even don t have them in stock The other way is to try out some parameters starting with the information delivered by the Identify Drive command 10 The break a sample program I realize that I ve already filled quite a few pages ag
27. offers some advantages One of the main features is that you don t have a serial data stream with fixed bit rate between controller and drive Thus there s no need for conditioning the signals for the interface and you can use any bit rate As a result the hard disk performance is limited by the drive technology not by the interface s bit rate This is one reason why today s drives are so much faster than the older ones And technologies like Seagate s ZBR Zone Bit Recording are possible with hardware independent interfaces There is another main feature of bringing the controller into the disk drive Today s drives have very extensive checks for data security They store error correction codes ECC together with the sector data and automatically correct single bit errors so the sector need not be re read in those cases Additionally if a sector is found to be too unreliable it is internally marked as bad and the data is mapped to a spare sector usually there is one spare sector per track All this is absolutely transparent to the user So you now know the reason why today s intelligent drives don t have defect lists any more Since the PC s have such bad software and hardware too there is another thing the integrated controller can do translate virtual addressing information into physical That means that the IDE drive is able to emulate another drive with different parameters cylinder count number of heads and sect
28. ormal operation 12 3 Block Mode Commands Read Write Set Multiple C4 C6h By the use of these commands one can access disk data in larger blocks than the physical sector size Several sectors are grouped together and handled as a block of data However many drives don t support this mode I don t have detailed information regarding the parameters If a particular drive supports the block mode the details will surely be printed in its user manual 12 4 Power Commands E0 E6h except E4h The power commands are not supported by every IDE drive However if they are they are normally compat ible The power commands are commonly used within portable computers laptops notebooks handhelds or whatever the names are They allow for automatic or manual changing between normally four operation modes 12 Read Write Mode 4 2 W complete drive circuitry operating Idle Mode 2 0 W motor running r w circuitry turned off while no command is active Standby Mode 0 5 W motor stopped r w circuitry turned off interface active Sleep Mode n a everything stopped exit only with reset The power requirements mentioned in this table are those of my Conner 42 MB drive While no r w operation is in progress the drive normally is in idle mode also when being reset Read write mode is always automatically entered when a r w command is issued after completion of that command the drive enters idle mode again When the drive is put into standb
29. ors per track For the PC this is necessary because many PCs don t support drives with other than the historical 17 sectors per track and many do not support free configuration of the drive parameters only selection from a table is allowed Also some PCs mask off some bits of the cylinder number since the first controller only had a 10 bit cylinder register so nearly every IDE drive still supports an emulation mode with less than 1024 cylinders and 17 sectors per track 3 The IDE Interface As mentioned above the IDE interface is almost completely identical with a subset of the PC AT expansion bus so the drive can be connected almost directly to that The only things required externally are two select signals I O address decoding This gives us some information about how the interface works In a PC the drive is accessed directly by the CPU via I O accesses to registers internal to the drive The disk data is transferred via the 16 bit data bus but for compatibility to the older systems again only 8 bits are used for command and status information Besides the data bus there are the standard Intel type data strobe signals IORD and IOWR a few address lines and some special signals The connector is a 40 pin header not to be confused with the X T type IDE interface connector which is also a 40 pin header but needs somewhat different hardware and totally different software The IDE interface allows connection of two drives with o
30. rs are updated after command completion and after errors They are also used during drive initialization as the number of cylinders parameter The SDH register is a special register serving several functions SDH is an abbreviation for Sector size Drive and Head The bits of this register are arranged as follows Bit 7 Historical Extension Bit When zero CRC data is appended to the sector s data fields When set to one no CRC data is appended Since today s drives always use ECC error correction this bit must always be set no CRC Bit 6 5 Sector Size Since today s drives always have 512 byte sectors unchangeable by the user because PCs are not able to support other sizes these bits must always be 0 1 Bit 4 Drive This bit distinguishes between the two connected drives when using the master slave chain Single drives are always accessed with the drive bit set to zero Bit 3 0 Head number These four bits contain the head number that is the disk surface number for all following accesses Similar to the cylinder and sector number these bits are updated by the drive The head number field is also used for drive initialization to specify the number of heads The read only status register contains eight single bit flags It is updated at the completion of each command If the busy bit is active no other bits are valid The index bit is valid independent of the applied command The bit flags are Bit 7 Busy flag When th
31. take care of After a minimum of 80 ns the strobe signal has to be removed There are some more timing requirements but these are the main ones The above timing details might differ from drive to drive Always keep in mind that the IDE definition follows the PC AT system expansion bus and that official standards were not specified until two years ago when the TEEE finally defined some specifictions which many PC manufacturers are not following Unfortunately I found that the drives do not match their own specs in every detail For example I found that the address lines of my Conner drive a CP 3044 with 42 MB must be kept stable for much more than the specified setup time In addition the drive is very sensitive to spike noise on the address lines even if the noise appears long before an access is initiated I spent a great deal of time struggling with such unlucky details fixing other people s bugs 5 IDE Interface Registers Now that we ve covered the interface signals and their meaning and usage let s look at the registers of the interface We saw that there are eight addresses being accessed through CSO and two addresses through CS1 The following is a list of all the internal registers of an IDE drive CSO CS1 A2 Al AO Addr Read Function Write Function 0 1 0 0 0 1FO Data Register Data Register 0 1 0 0 1 1F1 Error Register Write Precomp Reg 0 1 0 1 0 1F2 Sector Count Sector Count 0 1 0 1 1 1F3 _ Sector Number Sector
32. te 70 7F C D H Exec Diagnostics 1 0 0 1 O 0 0 0 90 D Set Drive Parameters 10010 0 0 1 91 SC C D H Read Multiple 1 1 0 0 O 1 0 0 C4 SC SN C D H Write Multiple 1 1 0 0 0 1 0 1 SC SN C D H Set Multiple 1 1 0 0 0 1 1066 SC D Power Commands 1 1 1 0 0 x x x EO E6 SC D Read Sector Buffer 1 1 1 00 1 0 0 EA D Write Sector Buffer 1 1 1 0O 1 0 0 0 E8 D Identify Drive 1 1 1 O 1 1 0 0 EC D Cache On Off 117101 1 1 1 EF D WP Power Save 1 1 1 1 1 x x x F8 amp FD Parameters in parentheses are needed with some drives and ignored by others depending on the manufacturer and age Any required parameters must be valid before a command is started Although most of the commands are manufacturer dependent this usually does not raise problems For normal operation of the drive only the WD1010 s and few of the really common commands are needed Now let s have a look at the options In the Restore and Seek commands there is a four bit rate field This was originally intended to specify the step rate for head movements with a zero value meaning 35 us per step and all other values representing counts of 0 5 ms per step so that the range was from 0 5 to 7 5 ms The hard disk controller had a memory for each drive s step rate so the same value would be used for implied seeks later But very soon even with later ST 506 controller boards this step rate field became obsolete due to handshake mechanisms between controller and drive With
33. ter contains the same information as the status register in the task file The only difference is that reading this register does not imply interrupt acknowledge to reset a pending interrupt as the main status register does The digital output register contains only two valid data bits Bit 2 is the software reset bit which causes a drive reset when being set and bit 1 is the interrupt enable flag The drive address register simply loops back the drive select bit and head select bits of the currently selected drive This information normally is of no use for the programmer or user 6 Last Words Now that we had a look at the IDE interface we also see the physical limits of this interface definition With a fully expanded cylinder high register we are able to address up to 65536 cylinders with up to 16 heads and up to 256 sectors per track This results in a maximum addressable drive capacity of 128 gigabytes I think this should be enough for microcomputing However even if the PC AT BIOS limitations are encountered we could address 1024 cylinders with 16 heads and 64 sectors per tracks giving 512 megabytes maximum capacity This is also not bad at least for small 8 bit computer systems where complete application software packages require only about 100 kilobytes of disk space Next time I would like to talk about the applicable commands of IDE drives and give examples of how to write software that accesses those drives List of Abbrevi
34. terface access times The IO16 line informs the host of 16 bit transfers Since we already know that data transfers are always 16 bit and everything else is always 8 bit this is redundant however needed in the PC ATs for their ISA bus Line ACT Active is an output which can be used for driving a drive busy LED Line IRQ is an interrupt request line that goes active on some internal events if enabled by software Most IDE drives contain some jumpers that allow some options to be selected This normally includes at least master slave selection Sometimes the ACT signal may also be jumpered as an output signalling the presence of a second slave drive The default state of the jumpers normally need not be changed single drive no special situation All interface lines carry CMOS TTL compatible signal levels However some signals IRQ PDIAG IO16 ACT are able to drive higher currents Those details should be looked up in each drive s specifications for example the ACT output sinks 20 mA on my Conner drive more than enough for an LED Accessing the drive is done with the following sequence of operations First the address lines and the chip selects must be set according to the desired register address After some time a minimum of 25 ns IORD or IOWR is activated This causes the data to appear on the data lines when reading or to be written to the drive with the trailing edge of IOWR but there are setup and hold times to
35. today s IDE drives the four lower bits of those commands are generally ignored The Read and Write commands originally had an option flag M for multi sector m s transfers Today this flag is nonexistent For doing m s transfers the sector count register is simply set to the desired number of sectors to be processed But today s drives have another flag which originally wasn t there the Long flag L When it is set the ECC error correction data is transferred after the sector s data field I assume this was meant for error correction when there are too many errors for the drive to correct automatically However there is a very odd characteristic the ECC data is transferred in bytes through the data register This is the only case where the data register doesn t transfer word data By the way the number of ECC bytes differs from drive to drive but can be read out using the Identify Drive command All generations of hard disk controllers and IDE drives support the last option flag for Read Write commands the Retry Flag T Normally the drive retries to read write a sector after non fatal errors When this option flag is set automatic retries are disabled The Scan ID command also supports this option 9 The Commands I will now explain the commands and their parameters in detail To do this besides drawing on my own expe rience in IDE interfacing I collected detailed information and specifications from three different in
36. ure its results are placed in the error register In this special case the content of the error register has to be considered as a single byte value not as several bit flags There are the following error codes Olh no error detected 03h sector buffer error These codes are supported by Conner drives Maybe other manufacturers use more or different codes If the slave drive diagnostics failed the MSB of the error register is set leading to values of 8xh However even with single drive configurations this bit sometimes is accidently set It may be ignored then 9 8 Set Drive Parameters 91h An IDE only command again After power up or reset the drive can immediately be used in its default mode However the drive s logical parameters can be changed by setting them with this command This way the drive can be set up to different modes in order to emulate the parameters of another common drive The task file registers which are used with this command and the way in which they are used may differ Some drives are really flexible and allow any parameters that result in no more than the drive s real capacity Other drives for example my Conner CP 3044 support only two or three modes with fixed parameters So for their selection only part of the task file s registers are needed Most if not all drives will accept this command with valid parameters in the SC C and H registers even if not all the parameters are required defining the
37. var i integer begin Wait_DRQ i port IDE_Data specific to my IDE interface board for i 0 to 511 do Buf i port IDE_Data Read_SecBuf port IDE_CmdStat and 89 0 end function Write_SecBuf var Buf BufType boolean var i integer begin Wait_DRQ for i 0 to 511 do port IDE_Data Buf i Wait_Ready Write_SecBuf port IDE_CmdStat and 89 0 end 14 4 General access First access initialization procedure HD_Init Cyls Heads Secs integer begin port Dig_Out 6 delay 10 Drive Software Reset port Dig_Out 2 Wait_Ready port IDE_SecCnt Secs port IDE_CylLow 10 Cy1s port IDE_CylHigh hi Cyls port IDE_SDH pred Heads A0 16 IDE_Command Cmd_Initialize end 14 5 Data access Single sector read function HD_ReadSector Cyl Head Sec integer var Buf BufType boolean begin Wait_Ready port IDE_SecCnt 1 port IDE_SecNum Sec port IDE_CylLow 1o Cyl port IDE_CylHigh hi Cyl port IDE_SDH A0 Head IDE_Command Cmd_ReadSector HD_ReadSector Read_SecBuf Buf end 14 6 Data access Single sector write function HD_WriteSector Cyl Head Sec integer var Buf BufType begin Wait_Ready port IDE_SecCnt 1 port IDE_SecNun Sec port IDE_CylLow 10 Cy1 port IDE_CylHigh hi Cy1 port IDE_SDH A0 Head IDE_Command Cmd_WriteSector HD_WriteSector Write_SecBuf Buf end 17
38. y format an entire track of the hard disk exactly as it s done when formatting floppy disks The Format Track command is started similarly to the Write Sectors command first the task file must be set up then the command written to the command register After that the drive responds by setting the DRQ flag The host must then write data into the sector buffer until the DRQ flag is reset After that the command is executed For the format command the sector buffer must contain special data As with the index field array when formatting a floppy disk it must contain valid sector ID s for every physical sector of the track that will be formatted beginning at the start of the buffer Each sector ID in the buffer consists of two bytes The unused remainder of the buffer is ignored by the format command but must also be written for the DRQ signal to disappear The first byte of each sector ID is a flag byte The WD1010 knew only two different values for this descriptor 00h good sector 80h bad sector Today s IDE drives offer two more descriptor values 40h assign sector to alternate location 20h unassign alternate location for this sector We ll look further at these values below The second byte of each ID is the sector number byte It contains the number by which the related sector is referenced later during normal r w operation The ID fields in the sector buffer are assigned to the physical sectors created through formattin
39. y mode manually or automatically see below the drive motor r w circuit is shut down while the host interface remains active So when a command is issued which requires motor or r w operation the appropriate circuitry is automatically switched on again Once the sleep mode is entered there is no way out except for reset by means of hardware or software This is because even the drive s local processor and interface controller are stopped so there is no way to communicate with the drive However the task file can still be read As mentioned above there are six power commands 12 4 1 Set Standby Mode EOh Set Idle Mode Elh The drive will enter the desired mode immediately There are no parameters required If the drive already is in that mode the command will have no effect 12 4 2 Set Standby E2h or Idle E3h Mode with Auto Power Down These commands take a parameter in the sector count register If that parameter is non zero the Auto Power Down APD feature is enabled with a zero value APD is disabled When one of these commands is issued the drive immediately enters the desired mode If APD is enabled the drive will automatically enter standby mode after being in idle mode without activities for a given period of time This delay can be specified by means of the parameter for these two commands the SC register must contain the delay time in counts of 5 seconds The minimum delay of 60 seconds will be set if the SC re
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