Incorrect timeout handling in osThreadFlagsWait with osFlagsWaitAll #50
Description
The timeout handling in osThreadFlagsWait when using osFlagsWaitAll is incorrect and can lead to dramatically reduced timeouts.
Imagine a task waiting on two flags A and B with a timeout of 1000ms. The flag A is never set. The flag B is set once every 1ms. osThreadFlagsWait calls xTaskNotifyWait (0, clear, &nval, tout);, where tout is initially 1000ms. xTaskNotifyWait wakes up after 1ms when B is set. tout is then updated as follows:
td = xTaskGetTickCount() - t0;
if (td > tout) {
tout = 0;
} else {
tout -= td;
}t0 is the starting time of osThreadFlagsWait, so tout becomes 999ms.
xTaskNotifyWait is called again in a loop, so the next time B is set (2ms into the 1000ms timeout), tout becomes 997ms (instead of the correct 998ms). The third time (3ms into the 1000ms timeout), it becomes 997ms - 3ms = 994ms.
In other words, during each iteration, the remaining timeout tout is reduced by the total time waited, not by the time waited in that iteration. In the example above this results in the 1000ms timeout occurring after only 46ms have actually passed.
One possible fix is to change if (td > tout) to if (td > timeout) and tout -= td to tout = timeout - td.