How do you write a UART receiver ISR in FreeRTOS when I send a command and sometimes get a response quickly. I'm trying to use a binary semaphore but I have a race condition where I get the response before I execute the xSemaphoreTake(). Here's what I'm doing:
SemaphoreHandle_t msg_rcvd_semaphore = NULL;
uint32 my_data;
void xbee_rx_isr(void)
{
volatile uint32_t read_data;
// Ignore all but received byte interrupts
if((XBEE_UART_HW->INTR_RX_MASKED & SCB_INTR_RX_MASKED_NOT_EMPTY_Msk ) == 0) {
return;
}
// Clear UART "RX fifo not empty interrupt"
XBEE_UART_HW->INTR_RX = XBEE_UART_HW->INTR_RX & SCB_INTR_RX_NOT_EMPTY_Msk;
// Get the byte
my_data = Cy_SCB_UART_Get(XBEE_UART_HW);
//
BaseType_t xHigherPriorityTaskWoken = pdFALSE;
xSemaphoreGiveFromISR(msg_rcvd_semaphore, &xHigherPriorityTaskWoken);
if (xHigherPriorityTaskWoken == pdTRUE) {
portYIELD_FROM_ISR(xHigherPriorityTaskWoken);
}
}
void task (void)
{
msg_rcvd_semaphore = xSemaphoreCreateBinary();
// Initialize the receiver here
// Send commands and block for their responses
for (;;) {
// Transmit a command
xbee_uart_put_string("my_command");
// MY PROBLEM: Sometimes the response (and ISR) comes before I execute the following
// xSemaphoreTake(), in which case xSemaphoreTake() hangs forever.
// Wait for response (with 100 ms timeout)
if (xSemaphoreTake(msg_rcvd_semaphore, pdMS_TO_TICKS(100u)) == pdPASS) {
// Process my_data
} else {
// Process timeout
}
}
}
