micropython · dpgeorge · Jul 23, 2025 · Jul 17, 2025 · Jul 17, 2025
diff --git a/ports/esp32/machine_uart.c b/ports/esp32/machine_uart.c
@@ -508,20 +508,21 @@ static bool mp_machine_uart_txdone(machine_uart_obj_t *self) {
 }
 
 static void mp_machine_uart_sendbreak(machine_uart_obj_t *self) {
-    // Save settings
+    // Calculate the length of the break, as 13 bits.
     uint32_t baudrate;
     check_esp_err(uart_get_baudrate(self->uart_num, &baudrate));
+    uint32_t break_delay_us = 13000000 / baudrate;
 
-    // Synthesise the break condition by reducing the baud rate,
-    // and cater for the worst case of 5 data bits, no parity.
-    check_esp_err(uart_wait_tx_done(self->uart_num, pdMS_TO_TICKS(1000)));
-    check_esp_err(uart_set_baudrate(self->uart_num, baudrate * 6 / 15));
-    char buf[1] = {0};
-    uart_write_bytes(self->uart_num, buf, 1);
+    // Wait for any outstanding data to be transmitted.
     check_esp_err(uart_wait_tx_done(self->uart_num, pdMS_TO_TICKS(1000)));
 
-    // Restore original setting
-    check_esp_err(uart_set_baudrate(self->uart_num, baudrate));
+    // Set the TX pin to output, pull it low, and wait for the break period.
+    mp_hal_pin_output(self->tx);
+    mp_hal_pin_write(self->tx, 0);
+    mp_hal_delay_us(break_delay_us);
+
+    // Restore original UART pin settings.
+    check_esp_err(uart_set_pin(self->uart_num, self->tx, self->rx, self->rts, self->cts));
 }
 
 // Configure the timer used for IRQ_RXIDLE

diff --git a/tests/extmod_hardware/machine_uart_irq_break.py b/tests/extmod_hardware/machine_uart_irq_break.py
@@ -19,18 +19,13 @@
     if "ESP32S2" in _machine or "ESP32C3" in _machine or "ESP32C6" in _machine:
         print("SKIP")
         raise SystemExit
-    # ESP32 needs separate UART instances for the test
-    recv_uart_id = 1
-    recv_tx_pin = 14
-    recv_rx_pin = 5
-    send_uart_id = 2
-    send_tx_pin = 4
-    send_rx_pin = 12
+    uart_id = 1
+    tx_pin = 4
+    rx_pin = 5
 elif "rp2" in sys.platform:
-    recv_uart_id = 0
-    send_uart_id = 0
-    recv_tx_pin = "GPIO0"
-    recv_rx_pin = "GPIO1"
+    uart_id = 0
+    tx_pin = "GPIO0"
+    rx_pin = "GPIO1"
 else:
     print("Please add support for this test on this platform.")
     raise SystemExit
@@ -42,22 +37,17 @@ def irq(u):
 
 # Test that the IRQ is called for each break received.
 for bits_per_s in (2400, 9600, 57600):
-    recv_uart = UART(recv_uart_id, bits_per_s, tx=recv_tx_pin, rx=recv_rx_pin)
-    if recv_uart_id != send_uart_id:
-        send_uart = UART(send_uart_id, bits_per_s, tx=send_tx_pin, rx=send_rx_pin)
-    else:
-        send_uart = recv_uart
-
-    recv_uart.irq(irq, recv_uart.IRQ_BREAK)
+    uart = UART(uart_id, bits_per_s, tx=tx_pin, rx=rx_pin)
+    uart.irq(irq, uart.IRQ_BREAK)
 
     print("write", bits_per_s)
     for i in range(3):
-        send_uart.write(str(i))
-        send_uart.flush()
+        uart.write(str(i))
+        uart.flush()
         time.sleep_ms(10)
-        send_uart.sendbreak()
+        uart.sendbreak()
         time.sleep_ms(10)
         if "esp32" in sys.platform:
             # On esp32 a read is needed to read in the break byte.
-            recv_uart.read()
+            uart.read()
     print("done")