add #26 double reset to DFU, only work with nrf52840 (won't work with nrf52832)

README.md

@@ -32,6 +32,7 @@ Get the code with following command:
 
 There are 2 pins **DFU & FRST** that bootloader will check upon reset/power
 
+- `Double Reset` Reset twice within 500 ms will enter DFU with UF2 and CDC support (only works with nRF52840)
 - `DFU = Low and FRST = High` Enter DFU with UF2 and CDC support
 - `DFU = Low and FRST = Low` Enter DFU with OTA, can be upgraded with mobile application such as Nordic nrfConnect/Toolbox
 - `DFU = High and FRST = Low` Factory Reset mode, erase firmware application and its data

src/linker/s132_v6.ld

@@ -14,7 +14,10 @@ MEMORY
   FLASH (rx) : ORIGIN = 0x74000, LENGTH = 0xA000 /* 40 KB */
 
   /** RAM Region for bootloader. */
-  RAM (rwx) :  ORIGIN = 0x20003000, LENGTH = 0x20007F80-0x20003000
+  RAM (rwx) :  ORIGIN = 0x20003000, LENGTH = 0x20007F7C-0x20003000
+
+  /* Location for double reset detection, no init */
+  DBL_RESET (rwx) :  ORIGIN = 0x20007F7C, LENGTH = 0x04
 
   /** Location of non initialized RAM. Non initialized RAM is used for exchanging bond information
    *  from application to bootloader when using buttonluss DFU OTA. 
@@ -67,6 +70,11 @@ SECTIONS
     KEEP(*(.uicrMbrParamsPageAddress))
   } > UICR_MBR_PARAM_PAGE
   
+  .dbl_reset(NOLOAD) :
+  {
+
+  } > DBL_RESET  
+
   /* No init RAM section in bootloader. Used for bond information exchange. */
   .noinit(NOLOAD) :
   {

src/linker/s140_v6.ld

@@ -17,11 +17,15 @@ MEMORY
   /* Avoid conflict with NOINIT for OTA bond sharing */
   RAM (rwx) :  ORIGIN = 0x20008000, LENGTH = 0x20040000-0x20008000
 
+  /* Location for double reset detection, no init */
+  DBL_RESET (rwx) :  ORIGIN = 0x20007F7C, LENGTH = 0x04
+  
   /** Location of non initialized RAM. Non initialized RAM is used for exchanging bond information
    *  from application to bootloader when using buttonluss DFU OTA. 
    */
   NOINIT (rwx) :  ORIGIN = 0x20007F80, LENGTH = 0x80
   
+
   /** Location of bootloader setting in flash. */
   BOOTLOADER_SETTINGS (rw) : ORIGIN = 0x000FF000, LENGTH = 0x1000
 
@@ -68,11 +72,17 @@ SECTIONS
     KEEP(*(.uicrMbrParamsPageAddress))
   } > UICR_MBR_PARAM_PAGE
 
+  .dbl_reset(NOLOAD) :
+  {
+
+  } > DBL_RESET
+
   /* No init RAM section in bootloader. Used for bond information exchange. */
   .noinit(NOLOAD) :
   {
 
   } > NOINIT
+
   /* other placements follow here... */
 }
 

src/main.c

@@ -98,6 +98,10 @@ void usb_teardown(void);
 #define DFU_MAGIC_SERIAL_ONLY_RESET     0x4e
 #define DFU_MAGIC_UF2_RESET             0x57
 
+#define DFU_DBL_RESET_MAGIC             0x5A1AD5      // SALADS
+#define DFU_DBL_RESET_DELAY             500
+#define DFU_DBL_RESET_MEM               0x20007F7C
+
 #define BOOTLOADER_VERSION_REGISTER     NRF_TIMER2->CC[0]
 #define DFU_SERIAL_STARTUP_INTERVAL     1000
 
@@ -119,6 +123,8 @@ STATIC_ASSERT( APPDATA_ADDR_START == 0x6D000);
 void adafruit_factory_reset(void);
 static uint32_t softdev_init(bool init_softdevice);
 
+uint32_t* dbl_reset_mem = ((uint32_t*)  DFU_DBL_RESET_MEM );
+
 // true if ble, false if serial
 bool _ota_dfu = false;
 bool _ota_connected = false;
@@ -146,7 +152,8 @@ int main(void)
   bool serial_only_dfu = (NRF_POWER->GPREGRET == DFU_MAGIC_SERIAL_ONLY_RESET);
 
   // start either serial, uf2 or ble
-  bool dfu_start = _ota_dfu || serial_only_dfu || (NRF_POWER->GPREGRET == DFU_MAGIC_UF2_RESET);
+  bool dfu_start = _ota_dfu || serial_only_dfu || (NRF_POWER->GPREGRET == DFU_MAGIC_UF2_RESET) ||
+                    (((*dbl_reset_mem) == DFU_DBL_RESET_MAGIC) && (NRF_POWER->RESETREAS & POWER_RESETREAS_RESETPIN_Msk));
 
   // Clear GPREGRET if it is our values
   if (dfu_start) NRF_POWER->GPREGRET = 0;
@@ -174,7 +181,34 @@ int main(void)
   // DFU + FRESET are pressed --> OTA
   _ota_dfu = _ota_dfu  || ( button_pressed(BUTTON_DFU) && button_pressed(BUTTON_FRESET) ) ;
 
-  if ( dfu_start || !bootloader_app_is_valid(DFU_BANK_0_REGION_START) )
+
+  bool const valid_app = bootloader_app_is_valid(DFU_BANK_0_REGION_START);
+
+  // App mode: register 1st reset and DFU startup (nrf52832)
+  if ( ! (dfu_start || !valid_app) )
+  {
+    // Register our first reset for double reset detection
+    (*dbl_reset_mem) = DFU_DBL_RESET_MAGIC;
+
+#ifdef NRF52832_XXAA
+    /* Even DFU is not active, we still force an 1000 ms dfu serial mode when startup
+     * to support auto programming from Arduino IDE
+     *
+     * Note: Supposedly during this time if RST is press, it will count as double reset.
+     * However Double Reset WONT work with nrf52832 since its SRAM got cleared anyway.
+     */
+    bootloader_dfu_start(false, DFU_SERIAL_STARTUP_INTERVAL);
+#else
+    led_on(LED_RED); // turn on LED to signal user
+    // if RST is pressed during this delay --> if will enter dfu
+    NRFX_DELAY_MS(DFU_DBL_RESET_DELAY);
+    led_off(LED_RED);
+#endif
+  }
+
+  (*dbl_reset_mem) = 0;
+
+  if ( dfu_start || !valid_app )
   {
     if ( _ota_dfu )
     {
@@ -204,15 +238,6 @@ int main(void)
       usb_teardown();
     }
   }
-#ifdef NRF52832_XXAA
-  else
-  {
-    /* Adafruit Modification
-     * Even DFU is not active, we still force an 1000 ms dfu serial mode when startup
-     * to support auto programming from Arduino IDE */
-    bootloader_dfu_start(false, DFU_SERIAL_STARTUP_INTERVAL);
-  }
-#endif
 
   // Adafruit Factory reset
   if ( !button_pressed(BUTTON_DFU) && button_pressed(BUTTON_FRESET) )