esp32/machine_uart: Implement the functionality of timeout_char arg.

Using it for the rx-timeout.  The value is given as ms, which is then
converted to character times.  A value of less than a character time will
cause the rx call to return immediately after 1 character, which may be
inefficient at high transmission rates.

Addresses #8778.

1 files changed, 10 insertions, 4 deletions

diff --git a/ports/esp32/machine_uart.c b/ports/esp32/machine_uart.c
index c0eedb80b..49ce78b1b 100644
--- a/ports/esp32/machine_uart.c
+++ b/ports/esp32/machine_uart.c
@@ -267,12 +267,18 @@ STATIC void machine_uart_init_helper(machine_uart_obj_t *self, size_t n_args, co
     }
 
     // set timeout_char
-    // make sure it is at least as long as a whole character (13 bits to be safe)
+    // make sure it is at least as long as a whole character (12 bits here)
     if (args[ARG_timeout_char].u_int != -1) {
         self->timeout_char = args[ARG_timeout_char].u_int;
-        uint32_t min_timeout_char = 13000 / baudrate + 1;
-        if (self->timeout_char < min_timeout_char) {
-            self->timeout_char = min_timeout_char;
+        uint32_t char_time_ms = 12000 / baudrate + 1;
+        uint32_t rx_timeout = self->timeout_char / char_time_ms;
+        if (rx_timeout < 1) {
+            #if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(4, 1, 0)
+            uart_set_rx_full_threshold(self->uart_num, 1);
+            #endif
+            uart_set_rx_timeout(self->uart_num, 1);
+        } else {
+            uart_set_rx_timeout(self->uart_num, rx_timeout);
         }
     }