samd/machine_uart.c: Fix unintended UART buffer allocation on init().

robert-hh · robert-hh · commit 78bc09230833 · 2025-03-09T11:39:12.000+01:00
The buffer was be reset on every call to uart.init(). If no sizes
were given, the buffer was be set to the default size 256. That made
problems e.g. with PPP.
This PR fixes it, keeping the buffer size if not deliberately changed
and allocating new buffers only if the size was changed.

Signed-off-by: robert-hh &lt;robert@hammelrath.com&gt;
diff --git a/ports/samd/machine_uart.c b/ports/samd/machine_uart.c
@@ -414,26 +414,34 @@ static void mp_machine_uart_init_helper(machine_uart_obj_t *self, size_t n_args,
     }
 
     // Set the RX buffer size if configured.
-    size_t rxbuf_len = DEFAULT_BUFFER_SIZE;
+    size_t rxbuf_len = self->read_buffer.size - 1;
     if (args[ARG_rxbuf].u_int > 0) {
         rxbuf_len = args[ARG_rxbuf].u_int;
         if (rxbuf_len < MIN_BUFFER_SIZE) {
             rxbuf_len = MIN_BUFFER_SIZE;
         } else if (rxbuf_len > MAX_BUFFER_SIZE) {
             mp_raise_ValueError(MP_ERROR_TEXT("rxbuf too large"));
         }
+        // Force re-allocting of the buffer if the size changed
+        if (rxbuf_len != (self->read_buffer.size - 1)) {
+            self->read_buffer.buf = NULL;
+        }
     }
 
     #if MICROPY_HW_UART_TXBUF
     // Set the TX buffer size if configured.
-    size_t txbuf_len = DEFAULT_BUFFER_SIZE;
+    size_t txbuf_len = self->write_buffer.size - 1;
     if (args[ARG_txbuf].u_int > 0) {
         txbuf_len = args[ARG_txbuf].u_int;
         if (txbuf_len < MIN_BUFFER_SIZE) {
             txbuf_len = MIN_BUFFER_SIZE;
         } else if (txbuf_len > MAX_BUFFER_SIZE) {
             mp_raise_ValueError(MP_ERROR_TEXT("txbuf too large"));
         }
+        // Force re-allocting of the buffer if the size changed
+        if (txbuf_len != (self->write_buffer.size - 1)) {
+            self->write_buffer.buf = NULL;
+        }
     }
     #endif
 
@@ -462,10 +470,14 @@ static void mp_machine_uart_init_helper(machine_uart_obj_t *self, size_t n_args,
         }
 
         // Allocate the RX/TX buffers.
-        ringbuf_alloc(&(self->read_buffer), rxbuf_len + 1);
+        if (self->read_buffer.buf == NULL) {
+            ringbuf_alloc(&(self->read_buffer), rxbuf_len + 1);
+        }
 
         #if MICROPY_HW_UART_TXBUF
-        ringbuf_alloc(&(self->write_buffer), txbuf_len + 1);
+        if (self->write_buffer.buf == NULL) {
+            ringbuf_alloc(&(self->write_buffer), txbuf_len + 1);
+        }
         #endif
 
         // Step 1: Configure the Pin mux.
@@ -503,6 +515,12 @@ static mp_obj_t mp_machine_uart_make_new(const mp_obj_type_t *type, size_t n_arg
     self->stop = 0;
     self->timeout = 1;
     self->timeout_char = 1;
+    self->read_buffer.size = DEFAULT_BUFFER_SIZE + 1;
+    self->read_buffer.buf = NULL;
+    #if MICROPY_HW_UART_TXBUF
+    self->write_buffer.size = DEFAULT_BUFFER_SIZE + 1;
+    self->write_buffer.buf = NULL;
+    #endif
     #if defined(pin_TX) && defined(pin_RX)
     // Initialize with the default pins
     self->tx = mp_hal_get_pin_obj((mp_obj_t)pin_TX);
