tests: uart_basic_api: Don't assume we can drink from IRQ firehose.

There're (at least) 2 UART TX interrupt causes: "tx fifo has more
room" and "transmission of tx fifo complete". Zephyr API has only
one function to enable TX interrupts, uart_irq_tx_enable(), so it's
fair to assume it enables interrupt for both conditions. But then
immediately after enabling TX IRQ, it will be fired with "tx fifo
has more room" cause. If ISR doesn't do anything to fill FIFO, on
some architectures, immediately after return from ISR, it will be
fired again (with no instruction progress in the main application
thread). That's exactly the situation with this test, and on ARM,
it leads to inifnite IRQ loop.

So, instead move call to uart_fifo_fill() inside ISR, and be sure
to disable TX IRQ after we transmitted enough characters.

Change-Id: Ibbd05acf96b01fdb128f08054819fd104d6dfae8
Signed-off-by: Paul Sokolovsky <[email protected]>

tests/drivers/uart/uart_basic_api/src/test_uart_fifo.c

@@ -37,13 +37,14 @@
 static volatile bool data_transmitted;
 static volatile bool data_received;
 static int char_sent;
-static const char *fifo_data = "This is a FIFO test.\r\n";
+static const char fifo_data[] = "This is a FIFO test.\r\n";
 
-#define DATA_SIZE	strlen(fifo_data)
+#define DATA_SIZE	(sizeof(fifo_data) - 1)
 
 static void uart_fifo_callback(struct device *dev)
 {
 	u8_t recvData;
+	static int tx_data_idx;
 
 	/* Verify uart_irq_update() */
 	if (!uart_irq_update(dev)) {
@@ -52,9 +53,27 @@ static void uart_fifo_callback(struct device *dev)
 	}
 
 	/* Verify uart_irq_tx_ready() */
-	if (uart_irq_tx_ready(dev)) {
-		data_transmitted = true;
-		char_sent++;
+	/* Note that TX IRQ may be disabled, but uart_irq_tx_ready() may
+	 * still return true when ISR is called for another UART interrupt,
+	 * hence additional check for i < DATA_SIZE.
+	 */
+	if (uart_irq_tx_ready(dev) && tx_data_idx < DATA_SIZE) {
+		/* We arrive here by "tx ready" interrupt, so should always
+		 * be able to put at least one byte into a FIFO. If not,
+		 * well, we'll fail test.
+		 */
+		if (uart_fifo_fill(dev,
+				   (u8_t *)&fifo_data[tx_data_idx++], 1) > 0) {
+			data_transmitted = true;
+			char_sent++;
+		}
+
+		if (tx_data_idx == DATA_SIZE) {
+			/* If we transmitted everything, stop IRQ stream,
+			 * otherwise main app might never run.
+			 */
+			uart_irq_tx_disable(dev);
+		}
 	}
 
 	/* Verify uart_irq_rx_ready() */
@@ -104,20 +123,16 @@ static int test_fifo_fill(void)
 	/* Verify uart_irq_tx_enable() */
 	uart_irq_tx_enable(uart_dev);
 
-	/* Verify uart_fifo_fill() */
-	for (int i = 0; i < DATA_SIZE; i++) {
-		data_transmitted = false;
-		while (!uart_fifo_fill(uart_dev, (u8_t *) &fifo_data[i], 1))
-			;
-		while (data_transmitted == false)
-			;
-	}
+	k_sleep(500);
 
 	/* Verify uart_irq_tx_disable() */
 	uart_irq_tx_disable(uart_dev);
 
-	/* strlen() doesn't include \r\n*/
-	if (char_sent - 1 == DATA_SIZE) {
+	if (!data_transmitted) {
+		return TC_FAIL;
+	}
+
+	if (char_sent == DATA_SIZE) {
 		return TC_PASS;
 	} else {
 		return TC_FAIL;