cpu/esp32: fix and improve UART initialization [backport 2023.01]

cpu/esp32/bootloader/sdkconfig.h

@@ -91,7 +91,7 @@ extern "C" {
  * If custom TX and RX are defined, use custom UART configuration for 2nd stage
  * bootloader.
  */
-#if defined(CONFIG_CONSOLE_UART_RX) && defined(CONFIG_CONSOLE_UART_RX)
+#if defined(CONFIG_CONSOLE_UART_TX) && defined(CONFIG_CONSOLE_UART_RX)
 #define CONFIG_ESP_CONSOLE_UART_CUSTOM      1
 #define CONFIG_ESP_CONSOLE_UART_TX_GPIO     CONFIG_CONSOLE_UART_TX
 #define CONFIG_ESP_CONSOLE_UART_RX_GPIO     CONFIG_CONSOLE_UART_RX

cpu/esp32/startup.c

@@ -147,6 +147,13 @@ static NORETURN void IRAM system_startup_cpu0(void)
     puf_sram_init((uint8_t *)&_sheap, SEED_RAM_LEN);
 #endif
 
+    /* initialize system call tables of ESP32x rom and newlib */
+    syscalls_init();
+
+    /* systemwide UART initialization */
+    extern void uart_system_init (void);
+    uart_system_init();
+
     /* initialize stdio */
     esp_rom_uart_tx_wait_idle(CONFIG_ESP_CONSOLE_UART_NUM);
     stdio_init();
@@ -228,16 +235,9 @@ static NORETURN void IRAM system_init (void)
     /* initialize the ISR stack for usage measurements */
     thread_isr_stack_init();
 
-    /* initialize system call tables of ESP32x rom and newlib */
-    syscalls_init();
-
     /* install exception handlers */
     init_exceptions();
 
-    /* systemwide UART initialization */
-    extern void uart_system_init (void);
-    uart_system_init();
-
     /* set log levels for SDK library outputs */
     extern void esp_log_level_set(const char* tag, esp_log_level_t level);
     esp_log_level_set("wifi", LOG_DEBUG);

cpu/esp_common/periph/uart.c

@@ -60,6 +60,7 @@
 #else /* defined(MCU_ESP8266) */
 
 #include "esp_rom_gpio.h"
+#include "esp_rom_uart.h"
 #include "hal/interrupt_controller_types.h"
 #include "hal/interrupt_controller_ll.h"
 #include "soc/gpio_reg.h"
@@ -68,6 +69,7 @@
 #include "soc/periph_defs.h"
 #include "soc/rtc.h"
 #include "soc/soc_caps.h"
+#include "soc/uart_pins.h"
 #include "soc/uart_reg.h"
 #include "soc/uart_struct.h"
 
@@ -166,30 +168,34 @@ int uart_init(uart_t uart, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg)
     assert(uart < UART_NUMOF);
 
 #ifndef MCU_ESP8266
-    /* reset the pins when they were already used as UART pins */
-    if (gpio_get_pin_usage(uart_config[uart].txd) == _UART) {
-        gpio_set_pin_usage(uart_config[uart].txd, _GPIO);
-    }
-    if (gpio_get_pin_usage(uart_config[uart].rxd) == _UART) {
-        gpio_set_pin_usage(uart_config[uart].rxd, _GPIO);
-    }
-
-    /* try to initialize the pins as GPIOs first */
-    if ((uart_config[uart].txd != GPIO_UNDEF &&
-         gpio_init(uart_config[uart].txd, GPIO_OUT)) ||
-        (uart_config[uart].rxd != GPIO_UNDEF &&
-         gpio_init(uart_config[uart].rxd, GPIO_IN_PU))) {
-        return -1;
-    }
+    assert(uart_config[uart].txd != GPIO_UNDEF);
+    assert(uart_config[uart].rxd != GPIO_UNDEF);
+
+    /* don't reinitialize the pins if they are already configured as UART pins */
+    if ((gpio_get_pin_usage(uart_config[uart].txd) != _UART) ||
+        (gpio_get_pin_usage(uart_config[uart].rxd) != _UART)) {
+
+        /* try to initialize the pins where the TX line is set and temporarily
+         * configured as a pull-up open-drain output before configuring it as
+         * a push-pull output to avoid a several msec long LOW pulse resulting
+         * in some garbage */
+        gpio_set(uart_config[uart].txd);
+        if (gpio_init(uart_config[uart].txd, GPIO_OD_PU) ||
+            gpio_init(uart_config[uart].txd, GPIO_OUT) ||
+            gpio_init(uart_config[uart].rxd, GPIO_IN_PU)) {
+            return -1;
+        }
 
-    /* store the usage type in GPIO table */
-    gpio_set_pin_usage(uart_config[uart].txd, _UART);
-    gpio_set_pin_usage(uart_config[uart].rxd, _UART);
+        /* store the usage type in GPIO table */
+        gpio_set_pin_usage(uart_config[uart].txd, _UART);
+        gpio_set_pin_usage(uart_config[uart].rxd, _UART);
 
-    esp_rom_gpio_connect_out_signal(uart_config[uart].txd,
-                                    _uarts[uart].signal_txd, false, false);
-    esp_rom_gpio_connect_in_signal(uart_config[uart].rxd,
-                                   _uarts[uart].signal_rxd, false);
+        esp_rom_uart_tx_wait_idle(uart);
+        esp_rom_gpio_connect_out_signal(uart_config[uart].txd,
+                                        _uarts[uart].signal_txd, false, false);
+        esp_rom_gpio_connect_in_signal(uart_config[uart].rxd,
+                                       _uarts[uart].signal_rxd, false);
+    }
 #endif /* MCU_ESP8266 */
 
     _uarts[uart].baudrate = baudrate;
@@ -247,6 +253,18 @@ void uart_system_init(void)
         /* reset all UART interrupt status registers */
         _uarts[uart].regs->int_clr.val = ~0;
     }
+#ifndef MCU_ESP8266
+    /* reset the pin usage of the default UART0 pins to GPIO to allow
+     * reinitialization and usage for other purposes */
+    gpio_set_pin_usage(U0TXD_GPIO_NUM, _GPIO);
+    gpio_set_pin_usage(U0RXD_GPIO_NUM, _GPIO);
+#if defined(CONFIG_CONSOLE_UART_TX) && defined(CONFIG_CONSOLE_UART_TX)
+    /* reset the pin usage of the UART pins used by the bootloader to
+     * _GPIO to be able to use them later for other purposes */
+    gpio_set_pin_usage(CONFIG_CONSOLE_UART_TX, _GPIO);
+    gpio_set_pin_usage(CONFIG_CONSOLE_UART_RX, _GPIO);
+#endif
+#endif
 }
 
 void uart_print_config(void)