RX630 Group Interrupt-mode UART Driver for RX630
Contents
1. Return Values Boolean result code True Data was available a character is returned in read_data argument False No data was available value of 0 is written to read_data argument Properties Prototyped in file uart h Description This function fetches one byte from a buffer that has been filled by the serial port receive interrupt handler As the SCI hardware receives new data on the serial bus the receive ISR transfers the data into a circular queue in RAM see section on interrupt handlers When the top address of the queue buffer is reached the queue position wraps back to the bottom address of the buffer and storage of the data continues A count of the number of unread bytes is added to by the receive data interrupt handler The sci_get_char function decrements that count by one each time it is called Eventually the count reaches 0 indicating that there is no more data in the receive queue to be processed If the receive queue contains unread data when sci_get_char is called then the byte at the current queue pointer position is copied into the location pointed to by the read_data argument and the result code true is returned If sci_get_char is called when the queue is empty then it sets the read data argument to zero and returns immediately with a false result code Reentrant e No Example Example showing this function being used static uint8 _t old_char uint8_t new_char Read a received character if s2. connection Click Reset Go to start the software Observe LEDs flash Observe introductory message print to terminal display g Sy Me oe ee Enter text on terminal and observe characters echoed back 7 The Software This driver uses interrupt events from the SCI peripheral to invoke the serial communications data transfers into and out of RAM based data queues This enables an application to be able to write and read data over the serial link with minimal latency The objective is to eliminate blocking on calls to the send and receive procedures At the application level data to be transmitted is written into a RAM queue immediately and the application can then carry on with other tasks With data in the transmit queue the transmit interrupt service routine begins sending out the data onto the serial bus in the background that is the transmit interrupt handler is only active briefly when the transmit data register is ready for another character and there is data remaining to be sent For the reception of data asynchronously it would be very wasteful for the application to continue waiting for data that could arrive at any time The receive data buffer full interrupt handler eliminates waiting by automatically running only whenever new data is received The application does not need to immediately respond to this event because the interrupt handler places the received data into a RAM queue where it can be accessed later by the applic
3. input signal become possible Unused pins should be handled as described under Handling of Unused Pins in the manual 2 Processing at Power on The state of the product is undefined at the moment when power is supplied The states of internal circuits in the LSI are indeterminate and the states of register settings and pins are undefined at the moment when power is supplied In a finished product where the reset signal is applied to the external reset pin the states of pins are not guaranteed from the moment when power is supplied until the reset process is completed In a similar way the states of pins in a product that is reset by an on chip power on reset function are not guaranteed from the moment when power is supplied until the power reaches the level at which resetting has been specified 3 Prohibition of Access to Reserved Addresses Access to reserved addresses is prohibited The reserved addresses are provided for the possible future expansion of functions Do not access these addresses the correct operation of LSI is not guaranteed if they are accessed 4 Clock Signals After applying a reset only release the reset line after the operating clock signal has become stable When switching the clock signal during program execution wait until the target clock signal has stabilized When the clock signal is generated with an external resonator or from an external oscillator during a reset ensure that the reset line is
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5. Description This function writes a byte to the serial port It uses buffered output for low latency If the SCI channel transmit data register is currently empty the write_data value gets copied directly into the data register and this function returns immediately with a true result indicating that the data was accepted Otherwise the data is stored in a transmit data queue and then the function returns with a true result indicating that the data was accepted A global variable g_uart_tx_ready is shared between the sci_put_char function and the transmit interrupt handler see Hardware Interrupts section as a flag used to coordinate this activity between the two procedures This procedure maintains its own private queue position counter that is reset when sci_uart_init is executed As each byte is added to the transmit queue the position in the queue is advanced and the count is incremented by one If the top address of the queue buffer is reached the position pointer is reset back to the bottom address of the buffer Any data accumulated in the queue will be written out by the transmit interrupt handler which will also take care of decrementing the count If the queue is full then this function returns immediately with a false result and the data is not written Reentrant e No Example Transmit a character to the serial port result sci_put_char A Special Notes e Acall to sci_uart_init must have been completed once before c
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7. QEN ESAS APPLICATION NOTE RX630 Group R01AN0820EU0101 Rev 1 01 Interrupt mode UART Driver for RX630 Oct 26 2011 Introduction The RX630 Group has a 13 channel communications interface SCI controller Among its configuration modes is the ability to operate as a Universal Asynchronous Receiver Transmitter UART This is commonly known as an RS232 serial port when used together with an RS232 I O line driver receiver transceiver The RSKRX630 development board has one SCI channel connected to an RS232 transceiver and is equipped with a DB9 serial cable connector which makes it a convenient platform for developing and demonstrating a UART communications software driver This application note describes a software driver that was created to demonstrate asynchronous communications using the SCI peripheral configured as a UART The software incorporates buffered interrupt driven input and output and serves as an example basis for a driver suitable for real time applications Together with this document there is a working C code HEW project that shows register level configuration and control of the RX630 SCI in UART mode Target Audience Those developing applications that require asynchronous serial communications using Renesas RX MCUs and who need examples that demonstrate configuration and operation of the SCI peripheral at the register level Target Device RX630 on RSKRX630 starter kit board Related Documents RX630 Group User s Man
8. UART The software uses buffered interrupt driven input and output and serves as an example basis for a driver suitable for real time applications The key benefits of this example code are its demonstration of the initialization of the SCI hardware and the use of the SCI interrupts to perform efficient non blocking serial I O The software is targeted specifically to the RSK RX630 development board but it can easily be adapted to other target boards that use Renesas RX MCUs The UART driver code is separated from the sample application code making it very portable Several convenient functions have been provided for accessing the driver in a platform flexible manner 2 Review of UART Basics UART stands for Universal Asynchronous Receiver Transmitter The job of a UART is to convert parallel byte data into a formatted serial data bit stream Each byte of data carried on the serial bus is self clocking It is in the form of a packet that optionally includes various bits for the purpose of identifying and verifying the data field of the transmission A UART typically interfaces to an RS232 serial bus using an RS232 standard line driver receiver IC The RX630 Serial Communications Interface is more than a UART but it can be configured to perform the typical UART function 3 Tools and Resources Things you will need e HEW High performance Embedded Workshop tool e RSKRX630_UART project HEW workspace package e RSKRX630 MCU development boa
9. UART Driver for RX630 Start SCIO_TEIO_isr_ Disable TX interrupts Set global transmitter ready flag variable true exit SCIO_TEIO_isr Figure 5 Transmit Completed interrupt service routine flow diagram The transmit complete TEI interrupt handler is invoked when a transmit operation has completed It just sets a global status flag that indicates the hardware is idle and ready for another transmit operation Start SCIO_RXIO_isr Yy Read RX data reg into local variable RX buffer overflow Clear Error No ORER bit still set pipelining Pointing Point to to top of received Yes bottom of data queue queue No Copy data into queue at current position m queue position and data count exit SCIO_RXIO_isr Figure 6 Receive data buffer full interrupt service routine flow diagram As the SCI hardware receives new data on the serial bus the receive ISR transfers the data into a circular queue in RAM When the top address of the queue buffer is reached the queue position wraps back to the bottom address of the buffer and storage of the data continues A running count of the number of bytes copied to the queue is maintained in a global variable g rx_count The count value is decremented by the sci_get_char function as the application processes the data in the queue This proced
10. alling this function e Adjust baud rate and or buffer size as required by the application to minimize queue full result RO1AN0820EU0101 Rev 1 01 Page 6 of 14 Oct 26 2011 RENESAS RX630 Group Interrupt mode UART Driver for RX630 Start sci_put_char y Enable TX interrupts Transmit data queue full Disable TX interrupts TX data register ready for a char No Yes Write byte passed in as argument directly y Store the argument byte in the transmit queue at the current position Y Increment transmit to TX data reg queue position Set global transmitter ready flag variable false of transmit data At top Yes queues Point back to bottom of queue No a 4 y Increment queue data count y Enable TX interrupts y y Set result code true Set result code false AA Return the result code sci_put_char End Figure 2 sci_put_char function flow diagram R01AN0820EU0101 Rev 1 01 Oct 26 2011 RENESAS Page 7 of 14 RX630 Group Interrupt mode UART Driver for RX630 8 3 sci_get_char Fetches a byte from receive buffer Format bool sci_get_char uint8 t read_data Parameters read_data Pointer to a location where the read data is to be copied to
11. ation Table 2 List of uart c functions Driver Function name Purpose sci_uart_init Initialize an SCI channel to operate as an asynchronous UART sci_put_char Writes a single byte to the serial port sci_get_char Transfers a byte from receive buffer that has been filled by the serial port receive interrupt handler sci_write_str Outputs a null terminated string from the serial port sci_read_count_get Gets the current count of unprocessed data in the read buffer sci_tx_interrupt_enable Called to enable transmit related interrupts sci_rx_interrupt_enable Called to enable the receive data ready and receive error interrupts sci_tx_interrupt_disable Disables the transmit related interrupts sci_rx_interrupt_disable Disables the receive data ready and receive error interrupts SCIO_TXI0O_isr ISR for the SCI TXI transmit data register empty interrupt Not callable SCIO_RXI0_isr ISR for the SCI RXI receive data register full interrupt Not callable SCIO_TEIO_isr ISR for the SCI TEI transmit ended interrupt Not callable RO1AN0820EU0101 Rev 1 01 Page 4 of 14 Oct 26 2011 RENESAS RX630 Group Interrupt mode UART Driver for RX630 8 SCI UART Driver Functions 8 1 sci_uart_init Prepares SCI channel as asynchronous UART Format void sci_uart_init void Parameters None Return Values None Properties Prototyped in file uart h Description This function configures I O pins set
12. ci_get_char amp new_char Data is returned in new_char old_char new_char Got a new character Do something with it else No data was available Try again later or report an error Special Notes A call to sci_uart_init must have been completed once before calling this function otherwise no new data will ever be read and the receive queue will remain empty Calling sci_get_char while the receive queue is empty can be avoided by first calling the function sci_read_count_get to check for a non zero count Limitations If the receive queue is filled before the application can consume the data new data received continues to be stored in the queue overwriting any unprocessed data remaining in that location Normally the application is expected to read the data from the queue before that happens With minor modifications this behavior could optionally cause an error to be flagged so that the application can be informed that data has been lost The buffer sizes are easily modifiable through a single define statement Currently an overrun condition can be determined by comparing the read count value to the buffer size value If the read count is greater than the buffer size then an overrun has occurred RO1AN0820EU0101 Rev 1 01 Page 8 of 14 Oct 26 2011 RENESAS RX630 Group Interrupt mode UART Driver for RX630 Start sci_get_char Does received data queue contain unread data Yes v Di
13. ci_read_count_get if num_in_rx_queue gt RX_QUEUE_SIZE 2 Receive queue is over half full Better start reading from it RO1AN0820EU0101 Rev 1 01 Page 11 of 14 Oct 26 2011 RENESAS RX630 Group Interrupt mode UART Driver for RX630 9 Hardware interrupt handlers The SCI interrupt handlers work interactively with higher level functions that fill data into a transmit queue and consume data from a receive queue In the case of both the transmit and receive queues the buffer areas are treated as circular buffers This prevents buffer out of bounds problems by wrapping back to the beginning when the end of the buffer is reached Start SCIO_TXIO_isr present in transmit No Yes y Clear global transmitter ready flag variable to false y Disable TX Copy data at current interrupts queue position to TX i data reg Vv Set global Increment transmit transmitter ready queue position flag variable true Pointing Point to to top of transmit Yes bottom of data queue queue Decrement queue data count exit SCIO_TXIO_isr Figure 4 Transmit data buffer empty interrupt service routine flow diagram This ISR is invoked when the SCI channel transmit data register empty interrupt request is generated When the application has data to transmit the sci_put_char function gets called which places the da
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15. gs e For the RX MCU the UART configuration is 8 data bits 1 stop bit no parity no flow control e Check the BAUDRATE for actual speed This will be defined in the uart c file The value is typically 115200 e Set the serial communication port settings for your terminal application to match the RSKRX630 UART program settings e When you get a correct serial connection you will see an introduction message on the PC terminal at board startup e Now you can type any character from the terminal keyboard and should see that character displayed on the terminal screen RO1AN0820EU0101 Rev 1 01 Page 3 of 14 Oct 26 2011 RENESAS RX630 Group Interrupt mode UART Driver for RX630 6 Sample Application Operation The program will receive character data over the UART into the RX630 MCU The program then echoes the same data back out onto the serial interface so that it shows up on for example a PC terminal program e g Microsoft HyperTerminal The sequence to run the sample application is summarized below See the referenced sections for more specific and detailed instructions for those steps 1 Compile and download the sample code as described in section 4 Building the project Connect RS232 port to a PC or serial data terminal See section 5 1 Connecting the RSK Board Confirm terminal port settings to be as follows 115200 baud 8 bits No parity 1 stop bit no handshake At this time instruct the terminal to activate its serial
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17. only released after full stabilization of the clock signal Moreover when switching to a clock signal produced with an external resonator or by an external oscillator while program execution is in progress wait until the target clock signal is stable 5 Differences between Products Before changing from one product to another i e to a product with a different part number confirm that the change will not lead to problems The characteristics of an MPU or MCU in the same group but having a different part number may differ in terms of the internal memory capacity layout pattern and other factors which can affect the ranges of electrical characteristics such as characteristic values operating margins immunity to noise and amount of radiated noise When changing to a product with a different part number implement a system evaluation test for the given product Notice 1 All information included in this document is current as of the date this document is issued Such information however is subject to change without any prior notice Before purchasing or using any Renesas Electronics products listed herein please confirm the latest product information with a Renesas Electronics sales office Also please pay regular and careful attention to additional and different information to be disclosed by Renesas Electronics such as that disclosed through our website 2 Renesas Electronics does not assume any liability for infringemen
18. rd e El or E20 emulator e RS232 cable with DB9 connectors e PC Terminal application such as Microsoft HyperTerminal or similar 4 Building the project To build the RSKRX630 UART program open the HEW workspace project for your Renesas RSKRX630 development board RSKRX630_UART hws Refer to the installation guide for your board for details on connecting the board and E1 or E20 emulator For help with the HEW development tool software refer to the High performance Embedded Workshop User s Manual or click to Help Help Topics in HEW The list in Table 1 shows the files that are contained in the RSKRX630 UART project workspace Table 1 C source files C header files dbsct c iodefine h hwsetup c Icd h Icd c rskRX6xxdef h led c sbrk h resetprg c stacksct h sbrk c uart h uart c vecttbl c RO1AN0820EU0101 Rev 1 01 Page 2 of 14 Oct 26 2011 RENESAS RX630 Group Interrupt mode UART Driver for RX630 5 Connections and Settings 5 1 Connecting the RSK Board e Connect the El or E20 Debugger Emulator to the RSK board and download the application e Connect a serial cable from your PC s RS232 COM port to the MCU running RSKRX630 UART program Note If your RSK board does not have a DSUB 9 connector installed already refer to the board schematic to find the UART RX and TX pins to connect directly Renesas RSK Board Figure 1 Connections for the UART demonstration project 5 2 Serial Port Settin
19. s mode serial port communication parameters and sets up interrupts It Must be called prior to performing any data transfers over the SCI serial channel Reentrant e No Example Initialize the SCI channel 0 as UART Do this before calling any other functions of the UART driver sci_uart_init Now ready to begin using the UART Special Notes Serial communications settings e Asynchronous e 8 bits data e No parity e stop bit e Hardware flow control off UART I O pins e P21 is designated as the RxDO pin e P20 is designated as the TxDO pin Input Clock Use PCLK divided by 1 Baud rate Set by define to 115200 Limitations The SCI channel number is hard coded in this sample code to SCI channel 0 and the I O pins are mapped to support the pin mapping of the RX630 RSK board for the RS232 serial port To support other configurations these values will need to be changed in the sci_uart_init function or alternately it could be re coded to employ a more dynamic form of configuration RO1AN0820EU0101 Rev 1 01 Page 5 of 14 Oct 26 2011 RENESAS RX630 Group Interrupt mode UART Driver for RX630 8 2 sci_put_char Writes a single byte to the serial port Format bool sci_put_char uint8 t write_data Parameters write_data The byte to be written Return Values Boolean result code True Data was accepted False Queue full data not written Properties Prototyped in file uart h
20. sable RX interrupts Copy the byte at the current data queue position to location No pointed to by read data pointer y Increment queue position Point to Yes bottom of queue Pointing to top of received data queue No y Decrement queue data count y Enable RX interrupts y y Clear read data value to O and set result code false Set result code true la y Return the result code End sci_get_char Figure 3 sci_get_char function flow diagram RO1AN0820EU0101 Rev 1 01 Page 9 of 14 Oct 26 2011 RENESAS RX630 Group Interrupt mode UART Driver for RX630 8 4 sci_write_str Outputs a null terminated string from the serial port Format uint32_t sci_write_str uint8_t source_string Parameters source_string Pointer to a null terminated string of byte data Return Values The number of bytes that were written Properties Prototyped in file uart h Description This function is a simple but useful example of a higher level procedure that can be built through use of the low level sci_put_char function sci_write_str repeatedly calls sci_put_char advancing through the source string data until the zero null terminator is encountered or the transmit queue returns full the internal call to sci_put_char fails The null terminator itself is not ou
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23. ta directly into the SCI transmit data register if transmit operation is currently idle or into the transmit data queue if the SCI is currently in the process of transmitting When a byte in the transmit data register has been transferred to the serial shift register the data register becomes available to accept new data and an interrupt request is generated resulting in this transmit ISR being invoked again A global variable g uart_tx_ready is shared between the sci_put_char function and this interrupt as a flag used to coordinate the interaction between these two procedures If the transmit queue contains data to send this ISR reads a byte from the queue and copies it to the transmit data register This procedure maintains its own private queue position counter that is reset when sci_uart_init is executed As data is retrieved from the queue the position is advanced If the top address of the queue buffer is reached the queue position wraps back to the bottom address of the buffer and data fetches continue from that location onward A running count of the number of bytes contained in the transmit queue is maintained in a global variable g_tx_count The count value is decremented by this procedure until it reaches 0 When the count reaches 0 this routine disables further interrupts and sets a global status flag to indicate that it is ready for more data RO1AN0820EU0101 Rev 1 01 Page 12 of 14 Oct 26 2011 RENESAS RX630 Group Interrupt mode
24. tput in any case A count of the total number of bytes actually written is returned to the caller Reentrant e No This function causes data to be written to the serial UART transmit queue Example uint32_t num_written uint8 t title _str RX630 UART Demonstration r n num written sci_write_str title_str if num written lt strlen title_str Transmit queue must have been full Handle error Special Notes If the transmit queue becomes full while this function is attempting to output the source string it will abort before the entire string has been written In this case only the number of bytes actually written will be returned RO1AN0820EU0101 Rev 1 01 Page 10 of 14 Oct 26 2011 RENESAS RX630 Group Interrupt mode UART Driver for RX630 8 5 sci_read_count_get Gets the current count of unprocessed data in the received data queue Format uint32_t sci_read_count_get void Parameters None Return Values The number of un read bytes remaining in the received data queue Properties Prototyped in file uart h Description sci_read_count_get is useful for checking to see how many bytes are in the receive buffer that have not yet been read by the application It can also be called before calling the sci_get_char function to avoid calling it when it is empty Reentrant e Yes Example Find out how much unprocessed data the receive queue is holding num_in_rx queue s
25. ual Hardware High performance Embedded Workshop User s Manual Contents Te Application OVervie W oops oc cecesec nunapa aa R a aa A EO AAR bees 2 2 Review of WART Basics mennina aa a E a aE a Ea EEA aaia 2 3 Tools and RESOUICES amp sitecscccesiceciiadenalicedacd sevedeeadbecsued aiaiai aana abd aaa aa aa anan aaa aaia ninaa 2 4 Building the project cece ceecceeeceeececeeeeeeeeeeeeeeeaeeeeaae sees eaaeeseaaeseeaaeseaeeeseaeeseaaeseaeesseeesaeseeaaeeseneesaas 2 5 Connections and Settings ccccceccceccceceeececeeeeeeeaeeeeaeeeeeeecaaeeeeaaesseneecaeeeeeaaesseeeeseeessaaeeseaaeenaeessaees 3 6 Sample Application Operation cccccecsceceeececeeeeeeeeceeneeceeaeeeeaaesseneeceaeeeeaaeeseaaeeseeeeesaesseaaeesieeesaees 4 Te WG SOWA E veseteveteckesaserccnetagsetegstede anen aaia aiai adede i odia oi iaa 4 8 SONUART Driver FUNCUONS aisrriseigi ineine anaiai e aae EEEE E a aAa AKERRA 5 9 Hardware interrupt hAandlers c ccccceeeeeeeeceeeee cece eeeeaeceeeeeceaeeecaaeeeeaeeecaeeesaaesseaeeseeeeescaeeesaeseaaeeeaas 12 Website and SuppOMt iccs sccccsesiet Avsicleeiehed dis dee dee deed a eaa aa d dagetla i etdeclie dle rrini aaia 14 RO1AN0820EU0101 Rev 1 01 Page 1 of 14 Oct 26 2011 RENESAS RX630 Group Interrupt mode UART Driver for RX630 1 Application Overview This application demonstrates the use of a software driver created to perform asynchronous serial communications using the SCI peripheral configured as a
26. ure maintains its own private queue position counter that is reset when sci_uart_init is executed RO1AN0820EU0101 Rev 1 01 Oct 26 2011 Page 13 of 14 RENESAS RX630 Group Website and Support Renesas Electronics Website http www renesas com Inquiries http www renesas com inquiry All trademarks and registered trademarks are the property of their respective owners RO1ANO0820EU0101 Rev 1 01 Oct 26 2011 Interrupt mode UART Driver for RX630 RENESAS Page 14 of 14 Revision Record Description Rev Date Page Summary 1 00 Oct 04 2011 First draft released 1 01 Oct 27 2011 Moved into new document template and minor edits A 1 General Precautions in the Handling of MPU MCU Products The following usage notes are applicable to all MPU MCU products from Renesas For detailed usage notes on the products covered by this document refer to the relevant sections of the document as well as any technical updates that have been issued for the products 1 Handling of Unused Pins Handle unused pins in accord with the directions given under Handling of Unused Pins in the manual The input pins of CMOS products are generally in the high impedance state In operation with an unused pin in the open circuit state extra electromagnetic noise is induced in the vicinity of LSI an associated shoot through current flows internally and malfunctions occur due to the false recognition of the pin state as an
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