From 755cfa95e4278c87df106656d9cdb6e023076c3a Mon Sep 17 00:00:00 2001
From: Glenn Engel <glenne@engel.org>
Date: Mon, 15 Feb 2021 07:49:52 -0800
Subject: [PATCH] Add USB connect timeout for app reset to UF2 or Serial via
 GPREGRET

---
 README.md  | 26 +++++++++++++++++++++-----
 src/main.c |  5 +++--
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/README.md b/README.md
index 83e7563..8b66875 100644
--- a/README.md
+++ b/README.md
@@ -57,6 +57,14 @@ There are two pins, `DFU` and `FRST` that bootloader will check upon reset/power
 - The `GPREGRET` register can also be set to force the bootloader can enter any of above modes (plus a CDC-only mode for Arduino).
 `GPREGRET` is set by the application before performing a soft reset.
 
+```c
+#include "nrf_nvic.h"
+void reset_to_uf2(void) {
+  NRF_POWER->GPREGRET = 0x57; // 0xA8 OTA, 0x4e Serial
+  NVIC_SystemReset();         // or sd_nvic_SystemReset();
+}
+```
+
 On the Nordic PCA10056 DK board, `DFU` is connected to **Button1**, and `FRST` is connected to **Button2**.
 So holding down **Button1** while clicking **RESET** will put the board into USB bootloader mode, with UF2 and CDC support.
 Holding down **Button2** while clicking **RESET** will put the board into OTA (over-the-air) bootloader mode.
@@ -69,7 +77,7 @@ For other boards, please check the board definition for details.
 
 ### Making your own UF2
 
-To create your own UF2 DFU update image, simply use the [Python conversion script](https://github.com/Microsoft/uf2/blob/master/utils/uf2conv.py) on a .bin file or .hex file, specifying the family as **0xADA52840**. If using a .bin file with the conversion script you must specify application address with the -b switch, this address depend on the SoftDevice size/version e.g S140 v6 is 0x26000 
+To create your own UF2 DFU update image, simply use the [Python conversion script](https://github.com/Microsoft/uf2/blob/master/utils/uf2conv.py) on a .bin file or .hex file, specifying the family as **0xADA52840**. If using a .bin file with the conversion script you must specify application address with the -b switch, this address depend on the SoftDevice size/version e.g S140 v6 is 0x26000
 
 To create a UF2 image from a .bin file:
 ```
@@ -105,6 +113,15 @@ You must have have a J-Link available to "unbrick" your device.
 Prerequisites
 
 - ARM GCC
+
+To install for macos
+
+```bash
+brew tap ArmMbed/homebrew-formulae
+brew install arm-none-eabi-gcc
+brew link --overwrite arm-none-eabi-gcc # if a prior version was present
+```
+
 - Nordic's [nRF5x Command Line Tools](https://www.nordicsemi.com/Software-and-Tools/Development-Tools/nRF-Command-Line-Tools)
 - [Python IntelHex](https://pypi.org/project/IntelHex/)
 
@@ -148,7 +165,7 @@ Makefile:90: *** BOARD not defined.  Stop
 If you get the following error ...
 
 ```
-$ make BOARD=feather_nrf52840_express all 
+$ make BOARD=feather_nrf52840_express all
 Compiling file: main.c
 /bin/sh: /usr/bin/arm-none-eabi-gcc: No such file or directory
 make: *** [_build/main.o] Error 127
@@ -160,6 +177,8 @@ the variable `CROSS_COMPILE` as below:
 $ make CROSS_COMPILE=/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/arm-none-eabi- BOARD=feather_nrf52832 all
 ```
 
+For other compile errors, check the gcc version with `arm-none-eabi-gcc --version` to insure it is at least 9.x.
+
 #### 2. `ModuleNotFoundError: No module named 'intelhex'`
 
 Install python-intelhex with
@@ -169,9 +188,6 @@ pip install intelhex
 ```
 
 
-
-
-
 #### 3. `make: nrfjprog: No such file or directory`
 
 Make sure that `nrfjprog` is available from the command-line. This binary is
diff --git a/src/main.c b/src/main.c
index cf05c1a..b665d6c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -170,9 +170,10 @@ int main(void)
 
   // Serial only mode
   bool serial_only_dfu = (NRF_POWER->GPREGRET == DFU_MAGIC_SERIAL_ONLY_RESET);
+  bool uf2_dfu = (NRF_POWER->GPREGRET == DFU_MAGIC_UF2_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 || uf2_dfu ||
                     (((*dbl_reset_mem) == DFU_DBL_RESET_MAGIC) && (NRF_POWER->RESETREAS & POWER_RESETREAS_RESETPIN_Msk));
 
   // Clear GPREGRET if it is our values
@@ -251,7 +252,7 @@ int main(void)
     }
 
     // Initiate an update of the firmware.
-    if (APP_ASKS_FOR_SINGLE_TAP_RESET())
+    if (APP_ASKS_FOR_SINGLE_TAP_RESET() || uf2_dfu || serial_only_dfu)
     {
       // If USB is not enumerated in 3s (eg. because we're running on battery), we restart into app.
       APP_ERROR_CHECK( bootloader_dfu_start(_ota_dfu, 3000, true) );