AVR350: XmodemCRC Receive Utility for AVR(R)
Contents
1. ACK SOH 0x03 OxFC Data CRC gt Duplicate Packet lt NACK SOH 0x04 OxFB Data CRC gt UART Framing Error on Any Byte lt NACK SOH 0x04 OxFB Data CRC gt Packet OK lt ACK SOH 0x05 OxFA Data CRC gt UART Overrun Error on Any Byte lt NACK SOH 0x05 OxFA Data CRC gt Packet OK lt ACK EOT gt Packet OK ACK Gets Garbled lt ACK EOT gt Packet OK Finished lt ACK AMEL Modifications to Receive Protocol AMEL Users may wish to count how many C s were sent during synchronization and after n number of tries abort the receive attempt For embedded applications it s not mandatory to have a 128 byte packet You could have 64 32 or even a 16 byte packet The sender of course would have to comprehend this For users that may want to migrate to Atmel s MegaAVR series there is a version of Xmodem that uses a 1Kbyte packet Or you can use an external SRAM with an AT90S4414 or an AT90S8515 to allow the increase in packet size If users do not wish to use the CRC method of data verification simply replace sending a C for synchronization with a NAK instead The sender will then send only the simple checksum of the data packet Of course the buffer size decreases by one and data errors may occur This modification would allow communication with equipment that supports only2. end get remainder of file recv_wait wait for error or buffer full packet validate_packet bufptr1 packet_number validate the packet gl recv_ptr bufptrl1 ve initialize buffer pointer before acknowledging respond packet ack or nak end of file transmission Recv_wait c include xmodem h extern struct global volatile unsigned char recv_ptr volatile unsigned char buffer_status volatile unsigned char recv_error volatile unsigned char t1_timed_out gl void recv_wait void 10 gl t1l1_timed_out false set in timer counter 0 overflow interrupt routine 1 second timeout 7 3728MHz 1024 7200 Hz 7200 Hz 138 8 us 1 seconds 138 8 us 7200 65536 7200 58336 e3e0 interrupt on ffff to 0000 transition TCNT1H 0xe3 TCNT1L 0xe0 load counter TCCR1IB 0x05 timer counter 1 clock 1024 wait for packet error or timeout while gl buffer_status amp amp gl t1_timed_out turnoff timer no more time outs needed TCCR1B 0x00 disable timer counter 1 clock AVR35O me A f F 35 Respond c include xmodem h extern struct global volatile unsigned char recv_ptr volatile unsigned char buffer_status volatile unsigned char recv_error volatile unsigned char t1_timed_out gl function prototypes void purge void void respond unsigned char packet clear buffer flag her
3. is sent to the sender and the three second time out starts again This process continues until the receiver receives a complete 133 byte packet Receiver This protocol NACKs the following conditions Considerations 1 Framing error on any byte 2 OverRun error on any byte 3 Duplicate packet 4 CRC error 5 Receiver timed out didn t receive packet within one second On any NAK the sender will re transmit the last packet Items one and two should be considered serious hardware failures Verify that sender and receiver are using the samebaud rate start bits and stop bits Item three is usually the sender getting an ACK garbled and re transmitting the packet Item four is found in noisy environments And the last issue should be self correcting after the receiver NAKs the sender 1472B AVR 05 02 res f F 3 5 Data Flow Diagram 1472B AVR 05 02 The data flow diagram below simulates a 5 packet file being sent Table 3 XmodemCRC Data Flow with Errors Sender lt Receiver ien Times Out after Three Seconds lt KC SOH 0x01 OxFE Data CRC gt Packet OK lt ACK SOH 0x02 OxFD Data CRC gt Line Hit during Data Transmission lt NACK SOH 0x02 OxFD Data CRC gt Packet OK lt ACK SOH 0x03 OxFC Data CRC gt Packet OK ACK Gets Garbled lt
4. Il interrupt on ffff to 0000 transition TCNT1H 0xe3 TCNT1L 0xe0 load counter TCCRIB 0x05 timer counter 1 clock 1024 while gl t1_timed_out read uart until done flush UDR TCCRIB 0x00 disable timer counter 1 clock Receive c include xmodem h extern struct global volatile unsigned char recv_ptr volatile unsigned char buffer_status volatile unsigned char recv_error volatile unsigned char t1_timed_out gl function prototypes unsigned char validate_packet unsigned char bufptr unsigned char packet_number void respond unsigned char packet void recv_wait void void sendc void void receive volatile unsigned char bufptr1 unsigned char packet status flag unsigned char packet_number packet_number 0x00 xmodem packets start at 1 gl recv_ptr bufptri1 point to recv buffer sendc send a c until the buffer gets full packet validate_packet bufptr1 packet_number validate packet 1 gl recv_ptr bufptri1 ve initialize buffer pointer before acknowledging AMEL 9 1472B AVR 05 02 Sy AMEL respond packet ack or nak while packet good if we nak ed above wait for packet 1 again recv_wait packet validate_packet bufptr1 packet_number validate packet 1 gl recv_ptr bufptr1 re initialize buffer pointer before acknowledging respond packet ack or nak while packet
5. the checksum method of data verification Software Routines were compiled using IAR s C compiler version 1 40 with max size optimiza tion The software was tested using Procomm DynaComm WinComm and Hyperterminal at baud rates up to 115 2K bps The receiver expects 8 start bits 1 stop bit and no parity bits The STK200 starter kit is used as a test platform with minor optional modifications A baud rate friendly crystal was used for this code Replace the 4 0 MHz crystal on the STK200 starter kit with a 7 3728 MHz crystal for proper operation If users wish to use the default crystal then modify the init routine to properly set up the uart baud rate regis ter UBRR Wait loops in the sendc and the recv_wait routines would also need modification To verify proper operation of this code the PORT D bit 2 should be connected to the switches on the starter kit Refer to the STK200 user manual for jumper locations and definitions Connect a 9 pin serial cable from a PC to the starter kit turn on power and use pushbutton two as a start of reception signal Use an ICEPRO Emulator an AT90S4414 8PC or an AT90S8515 8PC to execute the code Table 4 Routines Name Size in Bytes Function calcre 60 Calculates 16 bit CRC init 30 Low level Hardware Initialization main 280 Main purge 36 Reads UART Data Register for One Second receive 64 Main Receive Routine recv_wait 40 Waits until Buffer Full F
6. 1 38 4k with 7 3728Mhz crystal UBRR 7 57 6k with 7 3728Mhz crystal UBRR 3 115 2k with 7 3728Mhz crystal AMEL 7 1472B AVR 05 02 Sy Main c include xmodem h volatile unsigned char buf 133 struct global volatile unsigned volatile unsigned volatile unsigned volatile unsigned gl char char char char recv_ptr buffer_status recv_error t1l_timed_out unsigned char packet_number function prototypes AMEL void receive volatile unsigned char bufptr1 void purge void void init void void C_task main void init low level hardware initialization _SEI enable interrupts purge clear uart data register do while PIND amp 0x04 receive amp buf 0 while 1 main Purge c 8 include xmodem h extern struct global volatile unsigned volatile unsigned volatile unsigned volatile unsigned gl char char char char recv_ptr buffer_status recv_error t1_timed_out wait until pd2 pulled low wait 1 second for sender to empty its transmit buffer void purge void allow transmitter opportunity to unload its buffer AVR35O me 1472B AVR 05 02 A f F 35 unsigned char flush gl t1l_timed_out false 1 second timeout 7 3728MHz 1024 7200 Hz 7200 Hz 138 8 us 1 seconds 138 8 us 65536 7200 58336 Il 7200 e3e0
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8. AVR350 XmodemCRC Receive Utility for AVR Features Programmable Baud Rate Half Duplex 128 byte Data Packets CRC Data Verification Framing Error Detection OverRun Detection Less than 1K Bytes of Code Space C High level Language Code Introduction The Xmodem protocol was created years ago as a simple means of having two com puters talk to each other With its half duplex mode of operation 128 byte packets ACK NACK responses and CRC data checking the Xmodem protocol has found its way into many applications In fact most communication packages found on the PC today have a Xmodem protocol available to the user Theory of Operation Xmodem is a half duplex communication protocol The Receiver after receiving a packet will either acknowledge ACK or not acknowledge NACK the packet The original Xmodem protocol used a standard checksum method to verify the 128 byte data packet The CRC extension to the original protocol uses a more robust 16 bit CRC to validate the data block and is used here Xmodem can be considered to be receiver driven That is the Receiver sends an initial character C to the sender indi cating that it s ready to receive data in CRC mode The Sender then sends a 133 byte packet the Receiver validates it and responds with an ACK or a NACK at which time the sender will either send the next packet or re send the last packet This process is continued until an EOT is received at the Receiver side and is p
9. d out then if no uart framing or overrun errors then if first character in buffer is SOH then if second character in buffer is the next packet number then if second character in buffer plus the third character in buffer Oxff then compute CRC on packet data if CRC ok then increment packet number packet good else packet bad else bad packet number checksum else duplicate packet number else if first character in buffer is EOT then end of transmission else at least 1 byte had a framing or overrun error packet is bad else timed out without receiving all characters packet is bad 6 AVR350 me A f F 35 Code Listing Calcrc c include xmodem h int calecrc char ptr int count int crc char i cr 0 while count gt 0 cre cre int ptr lt lt 8 i 8 do if crc amp 0x8000 ere ere lt lt 1 0x1021 else ere cre lt lt 1 while i return crc Init c include xmodem h void init void portd bit 2 used to start data reception Pb7 Pb6 Pb5 Pb4 Pb3 Pb2 Pb1 PbO FiO O O O O O O oO Fpa 2 al 1 al T 1 1 1 DDRD Oxfb PORTD Oxff TCCRIA 0x00 timer counter 1 PWM disable TCCR1B 0x00 timer counter 1 clock disable TIMSK 0x80 enable timer counter 1 interrupt on overflow UCR 0x98 enable receiver transmitter and receiver interrupt UBRR 23 19 2k with 7 3728Mhz crystal UBRR 1
10. e very quickly gl buffer_status empty gl recv_error false if packet good packet dup while USR amp 0x20 UDR ACK else while USR amp 0x20 purge UDR NAK Sendc c include xmodem h extern struct global volatile unsigned char recv_ptr volatile unsigned char buffer_status volatile unsigned char recv_error volatile unsigned char t1l_timed_out gl void sendc void 3 second timeout 1472B AVR 05 02 when acking or nacking sender may respond framing and over run detection packet end wait till transmit register is empty now for the next packet wait till transmit register is empty let transmitter empty its buffer tell sender error AMEL 1 T A 12 AMEL 7 3728MHz 1024 7200 Hz 7200 Hz 138 8 us 3 seconds 138 8 us 21600 65536 21600 43936 aba0 interrupt on ffff to 0000 transition TCNT1H Oxab TCNT1L Oxa0 load counter TCCR1IB 0x00 disable timer counter 1 clock gl gl gl enable entry into while loops buffer_status empty tl_timed_out false recv_error false checked in validate_packet for framing or overruns send character C until we get a packet from the sender while gl buffer_status tell sender CRC mode while USR amp 0x20 wait till Data register is empty UDR CRCCHR signal tra
11. lag is Set or One Second Timeout respond 44 Sends an ACK or a NACK to the Sender sendc 88 Sends an ASCII C Character to the Sender until the Buffer Full Flag is Set timer 28 Timer1 Interrupt uart 80 Uart Receive Interrupt validate_packet 155 Validates Senders Packet 1472B AVR 05 02 A f F 35 Pseudo Code purge c initialize timerl counter for a 1 second delay read uart for 1 second receive c send a C character to sender until receive buffer is full validate received packet send an ack or a nak to sender if packet was bad then wait for new good packet while not end of transmission wait for buffer to fill validate the packet send an ack or a nak to sender recv_wait c initialize timerl counter for a 1 second delay wait till buffer is full or timeout respond c clear error flags if packet was good a duplicate packet or end of transmission then send an ack else purge senders uart transmit buffer send a nack sendc c initialize timerl counter for a 3 second delay clear error flags while buffer is not full character to sender signaling CRC mode send C enable timer counter wait for buffer full or timeout if timed out clear error flags restart timer uart c check uart for framing or overrun errors read byte from uart verify first byte in receive buffer is valid if buffer is full set buffer full flag AMEL T A 1472B AVR 05 02 AMEL validate_packet c if not time
12. ment packet good 14 AVR35O me A f F 35 else if bufptr 1 packet dup check for the end else if bufptr 0 EOT packet end else packet err else packet out return packet xmodem h include i08515 h include ina90 h pragma language extended define SOH 01 define EOT 04 define ACK 06 define NAK 25 define CRCCHR C define true Oxff define false 0x0 define full Oxff define empty 0x00 define bad 0x00 define good 0x01 define dup 0x02 define end 0x03 define err 0x04 define out 0x05 1472B AVR 05 02 block number checksum bad block number or same block number packet_number amp Oxff same block number ack got glitched packet is previous packet don t inc packet number AMEL T A 15 AIMEL T O Atmel Headquarters Corporate Headquarters 2325 Orchard Parkway San Jose CA 95131 TEL 1 408 441 0311 FAX 1 408 487 2600 Atmel Operations Memory 2325 Orchard Parkway San Jose CA 95131 TEL 1 408 441 0311 FAX 1 408 436 4314 RF Automotive Theresienstrasse 2 Postfach 3535 74025 Heilbronn Germany TEL 49 71 31 67 0 FAX 49 71 31 67 2340 Europe Microcontrollers Atmel Sarl 2325 Orchard Parkway Route des Arsenaux 41 San Jose CA 95131 Case Postale 80 TEL 1 408 441 0311 CH 1705 Fribourg FAX 1 408 436 4314 1150 East Cheyenne Mtn Blvd Colorado Springs CO 80906 TEL 1 719 576 3
13. nd does not make any commitment to update the information contained herein No licenses to patents or other intellectual property of Atmel are granted by the Company in connection with the sale of Atmel products expressly or by implication Atmel s products are not authorized for use as critical components in life support devices or systems ATMEL and AVR are the registered trademarks of Atmel Other terms and product names may be the trademarks of others amp Printed on recycled paper 1472B AVR 05 02 OM
14. nsmitter that I m ready in CRC mode 128 byte packets TCCRIB 0x05 timer counter 1 clock 1024 wait for timeout or recv buffer to fill while gl tl_timed_out amp amp gl buffer_status turn off timer TCCR1B 0x00 disable timer counter 1 clock if gl t1_timed_out start wait loop again gl til_timed_out false TCNT1H Oxab TCNT1L Oxa0 load counter start over AVR35O me 1472B AVR 05 02 A f F 35 Timert c include xmodem h extern struct global volatile unsigned char recv_ptr volatile unsigned char buffer_status volatile unsigned char recv_error volatile unsigned char t1_timed_out gl interrupt TIMER1_OVF1_vect void TIMER1_OVF1_interrupt void gl tl_timed_out true Uart c include xmodem h extern volatile unsigned char buf 133 extern struct global volatile unsigned char recv_ptr volatile unsigned char buffer_status volatile unsigned char recv_error volatile unsigned char t1l_timed_out gl interrupt UART_RX_vect void UART_RX_interrupt void use local pointer until IAR optimizes pointer variables better in the next release volatile unsigned char local_ptr local_ptr gl recv_ptr check for errors before reading data register reading UDR clears status if USR amp 0x18 Framing or over run error gl recv_error true will NAK sender in respond c always read a character otherwise an
15. other interrupt could get generated read status register before reading data register local_ptr UDR get char switch buf 0 determine if buffer full case SOH if local_ptr amp buf 132 1 gl buffer_status full local_ptr amp buf 0 AMEL 13 1472B AVR 05 02 Sy AMEL break IK case EOT gl buffer_status full local_ptr amp buf 0 break default gl buffer_status full first char unknown local_ptr amp buf 0 break gl recv_ptr local_ptr restore global pointer validate_packet c include xmodem h extern struct global volatile unsigned char recv_ptr volatile unsigned char buffer_status volatile unsigned char recv_error volatile unsigned char t1_timed_out gl function prototypes int calcrc char ptr int count unsigned char validate_packet unsigned char bufptr unsigned char packet_number unsigned char packet int crc packet bad if gl t1_timed_out if gl recv_error if bufptr 0 SOH valid start if bufptr 1 packet_number 1 amp Oxff sequential block number if bufptr 1 bufptr 2 Oxff block number and block number checksum are ok crc calcrc amp bufptr 3 128 compute CRC and validate it if bufptr 131 unsigned char cre gt gt 8 amp amp bufptr 132 unsigned char crc packet_number good packet ok to incre
16. roperly ACKed to the Sender After the initial handshake the receiver controls the flow of data through ACK ing and NAKing the Sender Table 1 XmodemCRC Packet Format Start of Header Packet Number Packet Number Packet Data 16 bit CRC AIMEL 8 bit AVR Microcontroller Application Note Rev 1472B AVR 05 02 AMEL Definitions The following defines are used for protocol flow control Table 2 Protocol Flow Control Symbol Description Value SOH Start of Header 0x01 EOT End of Transmission 0x04 ACK Acknowledge 0x06 NAK Not Acknowledge 0x15 C ASCII C 0x43 Byte one of the XmodemCRC packet can only have a value of SOH or EOT anything else is an error Bytes two and three form a packet number with checksum add the two bytes together and they should always equal Oxff Please note that the packet number starts out at 1 and rolls over to 0 if there are more than 255 packets to be received Bytes 4 131 form the data packet and can be anything Bytes 132 and 133 form the 16 bit CRC The high byte of the CRC is located in byte 132 Synchronization The Receiver starts by sending an ASCII C 0x43 character to the sender indicating it wishes to use the CRC method of block validating After sending the initial C the receiver waits for either a three second time out or until a buffer full flag is set If the receiver is timed out then another C
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