ATMEGA-128 UART issue

baiangel wrote on Tuesday, February 21, 2006:


I am trying to use both UARTS in ATMEGA128 port of the kernel (compiled with GCC). I have the following  situation: in one task, I send a message through UART0 to one node and I use xQueueReceive with timeout to receive an answer from the node. While this task is blocked on the queue, another task is sending a message to another node through UART1. The reception on both UARTS is done in an ISR. The problem is, that in this configuration the ISR is not always being entered. I have checked this using the following method: on evey entrance/exit of the ISR, I am toggling a pin of the MCU, thus counting the received symbols. With one channel of the scope I am tracing the received data (at the RX pin of the MCU) and with another channel I am tracing the toggling of the above mentioned pin. I found, that  not on evey byte I get an interupt. Also, when I disable one of the tasks, transmitting through the USART, the picture is just fine. I have 4 additional tasks, so the problem is not in the count of tasks. Do you have any idea where this problem comes from? Thank you!

I have tried this without the kernel (sending through UART0 in the main() and receiving through UART1 in an ISR). There was no such problem.

nobody wrote on Tuesday, February 21, 2006:

How are you sending to UART1?  Is this also using a Q?  A Q sounds good for the receive as it can be used to wake the task.  For Tx maybe the overhead is too much and as you don’t need to automatically wake a task a simply buffer could be used instead?

baiangel wrote on Wednesday, February 22, 2006:

I am sending to UART1 in a task, whcich is woken periodicaly (at about 100ms). The transmitting and the receiving in none of the UARTS occurs at the same time.