Creating new task in FreeRTOS for USART reception

Question

I am using EVK1105 development board with AVR Studio 5 as development IDE for my AVR project. I am using FreeRTOS in it. I have 3 USART ports on this board. One external module is connected to my AVR32 board via USART-RS232 mode. It sends me continuous serial data to my board on USART0 with 19230 baudrate, 7-databits, odd parity, stopbit-1 and normal-channel mode. I created a new task for this purpose. After each 9 data bytes it sends '\n' and '\r'. So in my task I keep on collecting the 9 databytes in a string buffer and then transmit it on USART1. I am using polling method to collect data from USAR0 which is receiving port. But I am facing problem in receiving data. I don't know if its timing issue or something or the scheduler switches the task while collects the data. But I don't get the required data.

Following are things I have already checked as troubleshooting 1. Connected my external module to my PC hyper-terminal which gives me perfect result. 2. Implemented the same thing of using receiving from USART0 and whatever received is transmitted to USART1 as without FreeRTOS. Its works fine.

Please suggest some idea what may be wrong. I am using a queue to communicate between Tx and Rx task to pass the string buffer from USART0 to USART1. Is it problem in handling queue? How can I troubleshoot the queue?

I am using a delay of 50ms in my infinite task loop in Rx Task. Can it create a problem? If I don't use any delay the OS crashes. Please suggest some good practices to create a new task in FreeRTOS so that I will not get any timing issue.

Answer 1

Are you still working on this? The statement of your problem is vague, but there I have several suggestions/leading questions. 1) You may want some documents to see what the registers are Get the giant datasheet pdfs at http://www.atmel.com/dyn/products/product_docs.asp?category_id=163&family_id=607&subfamily_id=2138&part_id=4117

2) In this and an earlier post you state that you have, in some cases, been able to RX data. You will need to find the USART HW initialization code from those example projects and get them into the freeRTOS example project. In particular calls to

gpio_enable_module() with {AVR32_USART0_RXD_0_0_PIN, AVR32_USART0_RXD_0_0_FUNCTION}

To connect to USART to CPU and i believe

InitRs232()

Just doing this requires poking around a lot of code - there's alot of dependencies.

2) What function are you calling to retrieve data from USART0? 19kbaud is approximately 2000bytes/sec or 1 byte/0.5ms, so 50ms polling is not nearly enough. I'd suggest that your RX task poll continuously (never sleep explicitly) but at a lower priority than the TX task.

3) Concentrate on debugging the RX task at the call to retrieve data. Use the debugger to look at the hardware registers for the usart. In particular

USART0 cr register AVR32_USART_CR_RXEN_MASK should be set to enable RX
USART0 csr register AVR32_USART_CSR_RXRDY_MASK will indicate if there is new data there You can also check the overlow flag to see if you have missed some data. When the read of USART0 rhr occurs it should be a byte that you sent.

If you are still working on this I can look into this a bit more.

Answer 2

For such a use case, I would not use a polling method with 50ms delay to retrieve data from UART peripheral. You can easily lose received data depending on the system load and UART reception buffer size.

At least use an interrupt on UART data reception that copies every received byte into a local buffer that will be read by your TX thread.

You can have an even better solution using a DMA channel to receive your data frame and be notified when 9 bytes have been received. I don't know if your AVR device has a DMA peripheral or not.