From e2523ffcaee9ee85cca847bf485b24e5654fd5bf Mon Sep 17 00:00:00 2001
From: Dan Halbert <halbert@halwitz.org>
Date: Thu, 29 Aug 2024 16:24:24 -0400
Subject: [PATCH] ESP32-C6: don't use LP UART; clean up if constructor failure

---
 .../seeed_xiao_esp32c6/mpconfigboard.mk       |  2 --
 ports/espressif/common-hal/busio/UART.c       | 20 ++++++++++++++++++-
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/ports/espressif/boards/seeed_xiao_esp32c6/mpconfigboard.mk b/ports/espressif/boards/seeed_xiao_esp32c6/mpconfigboard.mk
index e7ee13c027ac..9d95fe944496 100644
--- a/ports/espressif/boards/seeed_xiao_esp32c6/mpconfigboard.mk
+++ b/ports/espressif/boards/seeed_xiao_esp32c6/mpconfigboard.mk
@@ -6,5 +6,3 @@ IDF_TARGET = esp32c6
 CIRCUITPY_ESP_FLASH_MODE = qio
 CIRCUITPY_ESP_FLASH_FREQ = 80m
 CIRCUITPY_ESP_FLASH_SIZE = 4MB
-
-CIRCUITPY_ESP_USB_SERIAL_JTAG = 1
diff --git a/ports/espressif/common-hal/busio/UART.c b/ports/espressif/common-hal/busio/UART.c
index 3967af44dbd1..a48c3f723732 100644
--- a/ports/espressif/common-hal/busio/UART.c
+++ b/ports/espressif/common-hal/busio/UART.c
@@ -106,9 +106,22 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
     self->timeout_ms = timeout * 1000;
 
     self->uart_num = UART_NUM_MAX;
-    for (uart_port_t num = 0; num < UART_NUM_MAX; num++) {
+
+    // ESP32-C6 and ESP32-P4 both have a single LP (low power) UART, which is
+    // limited in what it can do and which pins it can use. Ignore it for now.
+    // Its UART number is higher than the numbers for the regular ("HP", high-power) UARTs.
+
+    // SOC_UART_LP_NUM is not defined for chips without an LP UART.
+    #if defined(SOC_UART_LP_NUM) && (SOC_UART_LP_NUM >= 1)
+    #define UART_LIMIT LP_UART_NUM_0
+    #else
+    #define UART_LIMIT UART_NUM_MAX
+    #endif
+
+    for (uart_port_t num = 0; num < UART_LIMIT; num++) {
         if (!uart_is_driver_installed(num)) {
             self->uart_num = num;
+            break;
         }
     }
     if (self->uart_num == UART_NUM_MAX) {
@@ -224,6 +237,7 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
     int rx_num = -1;
     int rts_num = -1;
     int cts_num = -1;
+
     if (have_tx) {
         claim_pin(tx);
         self->tx_pin = tx;
@@ -254,9 +268,13 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
         self->rts_pin = rs485_dir;
         rts_num = rs485_dir->number;
     }
+
     if (uart_set_pin(self->uart_num, tx_num, rx_num, rts_num, cts_num) != ESP_OK) {
+        // Uninstall driver and clean up.
+        common_hal_busio_uart_deinit(self);
         raise_ValueError_invalid_pins();
     }
+
     if (have_rx) {
         // On ESP32-C3 and ESP32-S3 (at least),  a junk byte with zero or more consecutive 1's can be
         // generated, even if the pin is pulled high (normal UART resting state) to begin with.