added bootloader force entry by input pin, projects changed back to build for the PIC18F2550

bootloader/src/main.c

@@ -5,10 +5,19 @@
  * Created on August 9, 2019, 6:14 PM
  */
 
+#include <xc.h>
+
 #include "usb.h"
 #include "bootloader.h"
 
-unsigned int uint_delay_counter;
+/**
+ * Comment this out to not check the bootloader entry override switch.
+ * THIS IS NOT RECOMMENDED!!
+ * If disabled the ONLY way to enter firmware update mode is by a jump from the application code.
+ * IF YOU FLASH BROKEN APPLICATION FIRMWARE YOU WILL HAVE A BRICK!!
+ * At that point the device can only be reprogrammed by a dedicated programmer such as the ICD or Pickit 3.
+ */
+#define ENABLE_HARDWARE_MODE_OVERRIDE
 
 /* Private prototypes */
 void main(void);
@@ -19,11 +28,26 @@ const unsigned int FlashSignatureWord __at(APP_SIGNATURE_ADDRESS) = APP_SIGNATUR
 
 void main(void)
 {
-    /**
-     * TODO: implement hardware IO-based method for forcing entry into bootloader
-     */
-     goto DoFlashSignatureCheck;
-    
+#ifdef ENABLE_HARDWARE_MODE_OVERRIDE
+    // immediately enter bootloader's firmware update mode if override switch is pressed
+    PORTA = 0x00; // initialize PORTA by clearing output data latches
+    ADCON1 = 0x0F; // disable analog functionality on PORTA pins
+    CMCON = 0x07; // disable comparators on PORTA pins
+    TRISAbits.RA0 = 1; // configure pin RA0 as input
+    if (PORTAbits.RA0 == 1)
+    {
+        // switch is NOT pressed. bootloader will execute as normal
+        ADCON1 = 0x00; // restore ADCON1 register to default state
+        TRISAbits.RA0 = 0; // restore RA0 pin direction to default state (output)
+        // start the signature check
+        goto DoFlashSignatureCheck;
+    }
+    else
+    {
+        // switch IS pressed. bypass signature check and immediately enter firmware update mode
+        BootMain();
+    }
+#endif
     // normal operation: verify the firmware signature is valid. if it isn't enter
     // bootloader (fw update) mode so valid firmware can be flashed
 DoFlashSignatureCheck:
@@ -50,7 +74,7 @@ DoFlashSignatureCheck:
     BootMain();
 }
 
-void BootMain(void) __at(0x30)
+void BootMain(void) __at(BOOTLOADER_ENTRYPOINT)
 {
     //Make sure interrupts are disabled for this code (could still be on,
     //if the application firmware jumped into the bootloader via software methods)