What will happen if a task is receiving data from a queue when an interrupt comes,and the interrupt send data to the same queue using the api function?
Can anyone give a efficient solution of serial receiving if the length of data to be received is unknown, how to handle the possible buffer overflow?

Regards!
wfrancis

You don't need to worry about mutual exclusion on a queue - the kernel takes care of all that for you.

Generally the most efficient way of receiving data would be to turn all FIFOs and DMA that is available on. Then either have the DMA place all received data into a buffer and interrupt a task to process the data if necessary, or have the UART interrupt a task to process the data when either there is enough data to process, a complete message has been received (as determined by the interrupt service routine), or there is a break in the transmission.

The interrupt can signal events to the task, and in so doing unblock the task, using either a binary or counting semaphore as appropriate for your application.

Do not use a queue to pass individual characters between an interrupt and task unless the data rate is low. The examples in the FreeRTOS download do this to demonstrate the mechanism but also to deliberately load up the system with interrupt and processing overhead to test the port is working correctly.

Regards.