uart: fix esp32c3 uart output garbage value after resetting

components/driver/uart.c

@@ -197,10 +197,19 @@ static void uart_module_enable(uart_port_t uart_num)
 {
     UART_ENTER_CRITICAL(&(uart_context[uart_num].spinlock));
     if (uart_context[uart_num].hw_enabled != true) {
-        if (uart_num != CONFIG_ESP_CONSOLE_UART_NUM) {
-            periph_module_reset(uart_periph_signal[uart_num].module);
-        }
         periph_module_enable(uart_periph_signal[uart_num].module);
+        if (uart_num != CONFIG_ESP_CONSOLE_UART_NUM) {
+        // Workaround for ESP32C3: enable core reset
+        // before enabling uart module clock
+        // to prevent uart output garbage value.
+        #if SOC_UART_REQUIRE_CORE_RESET
+            uart_hal_set_reset_core(&(uart_context[uart_num].hal), true);
+            periph_module_reset(uart_periph_signal[uart_num].module);
+            uart_hal_set_reset_core(&(uart_context[uart_num].hal), false);
+        #else
+            periph_module_reset(uart_periph_signal[uart_num].module);
+        #endif
+        }
         uart_context[uart_num].hw_enabled = true;
     }
     UART_EXIT_CRITICAL(&(uart_context[uart_num].spinlock));

components/esp32c3/system_api_esp32c3.c

@@ -31,6 +31,7 @@
 #include "soc/rtc.h"
 #include "soc/syscon_reg.h"
 #include "soc/system_reg.h"
+#include "soc/uart_reg.h"
 #include "hal/wdt_hal.h"
 
 /* "inner" restart function for after RTOS, interrupts & anything else on this
@@ -99,6 +100,10 @@ void IRAM_ATTR esp_restart_noos(void)
 
     REG_WRITE(SYSTEM_CORE_RST_EN_REG, 0);
 
+    // Reset uart0 core first, then reset apb side.
+    // rom will clear this bit, as well as SYSTEM_UART_RST
+    SET_PERI_REG_MASK(UART_CLK_CONF_REG(0), UART_RST_CORE_M);
+
     // Reset timer/spi/uart
     SET_PERI_REG_MASK(SYSTEM_PERIP_RST_EN0_REG,
                       SYSTEM_TIMERS_RST | SYSTEM_SPI01_RST | SYSTEM_UART_RST);

components/hal/esp32c3/include/hal/uart_ll.h

@@ -58,9 +58,8 @@ typedef enum {
     UART_INTR_CMD_CHAR_DET     = (0x1 << 18),
 } uart_intr_t;
 
-static inline void uart_ll_reset_core(uart_dev_t *hw) {
+static inline void uart_ll_set_reset_core(uart_dev_t *hw, bool core_rst_en) {
-    hw->clk_conf.rst_core = 1;
+    hw->clk_conf.rst_core = core_rst_en;
-    hw->clk_conf.rst_core = 0;
 }
 
 static inline void uart_ll_sclk_enable(uart_dev_t *hw) {

components/hal/include/hal/uart_hal.h

@@ -124,6 +124,16 @@ typedef struct {
  */
 #define uart_hal_is_tx_idle(hal)  uart_ll_is_tx_idle((hal)->dev)
 
+/**
+ * @brief  Configure the UART core reset
+ *
+ * @param  hal Context of the HAL layer
+ * @param  Set true to enable the core reset, otherwise set it false
+ *
+ * @return None
+ */
+#define uart_hal_set_reset_core(hal, core_rst_en)  uart_ll_set_reset_core((hal)->dev, core_rst_en)
+
 /**
  * @brief  Read data from the UART rxfifo
  *

components/soc/esp32c3/include/soc/soc_caps.h

@@ -229,6 +229,7 @@
 
 #define SOC_UART_SUPPORT_RTC_CLK    (1)
 #define SOC_UART_SUPPORT_XTAL_CLK   (1)
+#define SOC_UART_REQUIRE_CORE_RESET (1)
 
 // UART has an extra TX_WAIT_SEND state when the FIFO is not empty and XOFF is enabled
 #define SOC_UART_SUPPORT_FSM_TX_WAIT_SEND   (1)