The FreeRTOS USART support does not support the concept of a timeout value for the serial transaction. The current technique is to assume that the transfer will always block till it receives a character. In an RTOS environment, this may not (probably not) be the desired functionality. The function usartosread containts the notion of a timeoout value, but it is always set to ~0 which means wait forever. All that is needed is to set this a value to a of number of ticks to wait and you would have the desired operation. There would be a couple of ways to do this. One is to include a timeout parameter in the call to usartosread. This would be the most straight forward way to do this. However, there are probably lots of code pieces that would break. Another is to create another version of the function with the new parameter included. However, having two function names which almost do the same thing is always confusing.. A third way would be to leave the function call alone and include a way to update the timeout parameter transparently. To perform the third method, we would set up a table of timeout values that would represent the current timeout for a given iodescr value. We would do a lookup in table to see if there was a current timeout value for this iodescr value. If so, the value of timeout (in the function usartosread) would be set to this value and the timeout function would work normally. If there was no entry in the table, the function would return the original value of ~0 which would imply infinite wait as it currently does. The new code would consist of 4 functions: 1) initdevicetimeouttable This would initialize the search table so that no devices had a timeout. 2) finddeviceindex This would find the desired iodescr value in a table and return the timeout value or ~0 if there was no entry in the table. 3) setdevicetimeout This would set the timeout to a desired value for a given iodescr. 4) getdeevicetimeout This would find the value of the timeout for a given iodescr or ~0 if there was no entry in the table. The one line in the usartosread function that would change would be the iniitialization of the variable timeout. Currently this initialization is: uint32t timeout = ~0; This would change to: uint2t = getdevicetimeout(io_descr); For device calls where timeout is unimportant, the existing code would work the same as it always has. Where it is important to include an appropriate timeout value, an additional function call before the call to ioread would look like this: setdevicetimeout(&USART1,timeout_value); That call would set and keep the timeout value for that iodescr value (USART1 in this case) until it was changed. Any other ioread calls to a different iodescr value (USART2 or USART5 for instance) would behave as they do today. These functions could included in the halusartos.c file or put in a separate file. If they are put in the halusartos.c file, there would probably also need to be forward declarations in hal_usart.h. I have included three files: halusartostimeoutfix.c which is an update to halusartos.c (note that this also includes the modifications from a previous posting on losing characters) os_timeout.h which is an include file for the timeout functions os_timeout.h which is the implementation of the timeout functions.

See here: https://sourceforge.net/p/freertos/discussion/382005/thread/2e4555b21d/ which notes that these are not actually FreeRTOS functions but functinos provided by the vendor.