feat: Add UART support for slip frame receive

Author: Dzarda7

esp-stub-lib

@@ -5,7 +5,11 @@
  */
 
 #include <stddef.h>
+#include <stdbool.h>
+#include <stdint.h>
 #include <esp-stub-lib/flash.h>
+#include <esp-stub-lib/rom_wrappers.h>
+#include <target/uart.h>
 #include "slip.h"
 #include "command_handler.h"
 
@@ -19,7 +23,25 @@ __asm__(
     "j esp_main;");
 #endif //ESP8266
 
-static uint8_t s_command_buffer[MAX_COMMAND_SIZE] __attribute__((aligned(4)));
+static void uart_rx_interrupt_handler()
+{
+    // This also resets the interrupt flags
+    uint32_t intr_flags = stub_target_uart_get_intr_flags(UART_NUM_0);
+
+    if ((intr_flags & UART_INTR_RXFIFO_FULL) || (intr_flags & UART_INTR_RXFIFO_TOUT)) {
+        uint32_t count = stub_target_uart_get_rxfifo_count(UART_NUM_0);
+
+        for (uint32_t i = 0; i < count; i++) {
+            uint8_t byte = stub_target_uart_read_rxfifo_byte(UART_NUM_0);
+            stub_lib_uart_tx_one_char(byte);
+            slip_recv_byte(byte);
+
+            if (slip_is_frame_complete() || slip_is_frame_error()) {
+                break;
+            }
+        }
+    }
+}
 
 void esp_main(void)
 {
@@ -34,6 +56,10 @@ void esp_main(void)
     void *flash_state = NULL;
     stub_lib_flash_init(&flash_state);
 
+    stub_target_uart_wait_idle(UART_NUM_0);
+    stub_target_uart_init(UART_NUM_0, 115200);
+    stub_target_uart_intr_attach(UART_NUM_0, 5, uart_rx_interrupt_handler, UART_INTR_RXFIFO_FULL | UART_INTR_RXFIFO_TOUT);
+
     // Send OHAI greeting to signal stub is active
     const uint8_t greeting[4] = {'O', 'H', 'A', 'I'};
     slip_send_frame(&greeting, sizeof(greeting));