Add software method to enter bootloader (#2)

Author: bessman

src/main.c

@@ -6,20 +6,26 @@
  * (RC5) is grounded, the device will stay in bootloader mode even if an
  * application exists. While in bootloader mode, a new application can be
  * flashed with the Unified Bootloader Host Application, or a similar tool.
- * 
+ *
  * From PSLab V6 revision onwards, there is a push button attached to BOOT pin
  * with a label `BOOT`. Holding this button down at power up or when clicking on
- * `Read Device Settings` in Unified Bootloader application will switch from  
+ * `Read Device Settings` in Unified Bootloader application will switch from
  * main application to bootloader mode where one can flash a new firmware.
  */
+#include <stdbool.h>
+#include <stdint.h>
 
 #include "mcc_generated_files/system.h"
 #include "mcc_generated_files/boot/boot_process.h"
 #include "mcc_generated_files/pin_manager.h"
+#include "mcc_generated_files/uart1.h"
 
 #include "delay.h"
 #include "rgb_led.h"
 
+bool received_magic_number(void);
+bool is_boot_btn_pressed(void);
+
 int main(void) {
     // Initialize the device.
     SYSTEM_Initialize();
@@ -33,25 +39,53 @@ int main(void) {
     DELAY_ms(200);
     Light_RGB(32, 8, 16);
 
-    BOOT_PIN_SetDigitalOutput();
-    BOOT_PIN_SetHigh();
-    DELAY_us(1000); // Wait for BOOT to go high.
-
+    // If no application is detected in program area, stay in boot.
+    bool const app_detected = BOOT_Verify();
 
-    // If BOOT is grounded or no application is detected, stay in bootloader.
-    if (BOOT_PIN_GetValue() && BOOT_Verify()) {
+    if (app_detected && !is_boot_btn_pressed() && !received_magic_number()) {
         BOOT_StartApplication();
-    } else {
-        uint16_t i = 0;
+    }
 
-        while (1) {
-            // Monitor serial bus for commands, e.g. flashing new application.
-            BOOT_ProcessCommand();
+    for (uint16_t i = 0; 1; ++i) {
+        // Monitor serial bus for commands, e.g. flashing new application.
+        BOOT_ProcessCommand();
 
-            // Blink system LED while in bootloader mode.
-            if (!i++) STATUS_LED_Toggle();
-        }
+        // Blink system LED while in bootloader mode.
+        if (!i) STATUS_LED_Toggle();
     }
 
     return 1;
 }
+
+/**
+ * @brief After reset, host may send magic number stay in bootloader mode.
+ * 
+ * @return bool 
+ */
+bool received_magic_number(void) {
+    uint8_t magic[4] = {0xAD, 0xFB, 0xCA, 0xDE};
+    bool match = true;
+
+    for (uint8_t i = 0; i < 4; ++i) {
+        if (UART1_IsRxReady()) {
+            match = match && (magic[i] == UART1_Read());
+        } else {
+            match = false;
+        }
+    }
+
+    return match;
+}
+
+/**
+ * @brief If the BOOT button is pressed, stay in bootloader mode.
+ * 
+ * @return bool
+ */
+bool is_boot_btn_pressed(void) {
+    BOOT_PIN_SetDigitalOutput();
+    BOOT_PIN_SetHigh();
+    DELAY_us(1000); // Wait for BOOT to go high.
+    return !BOOT_PIN_GetValue();
+
+}