====== SAMD21 Bootloader ======


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==== ... with a Raspberry Pi ====

One has to install OpenOCD on a Raspberry Pi (RaspbianBuster):\\
Update and install some tools:
  $ sudo apt-get update
  § sudo apt-get install git autoconf libtool make pkg-config libusb-1.0-0 libusb-1.0-0-dev htop
Download OpenOCD from [[http://openocd.zylin.com/#/admin/projects/openocd]]:
  $ git clone http://openocd.zylin.com/openocd
Compile:
  $ cd openocd-code
  $ ./bootstrap
  $ ./configure --enable-sysfsgpio --enable-bcm2835gpio
  $ make
  $ sudo make install
List all Interfaces:
  $ cd /usr/local/share/openocd/scripts/interface
  $ ls
Make a Folder and Download the Bootloader:
  $ cd ~
  $ mkdir bootloader
  $ cd bootloader
  $ wget https://github.com/arduino/ArduinoCore-samd/raw/master/bootloaders/zero/samd21_sam_ba.bin
Make a Configuration File:
  $ nano openocd.cfg
and add:
  source [find interface/raspberrypi2-native.cfg]
  transport select swd
     
  set CHIPNAME at91samd21g18
  source [find target/at91samdXX.cfg]
  
  reset_config  srst_nogate
  
  adapter srst delay 400
  adapter srst pulse_width 100
  
  bcm2835gpio_swd_nums 25 24
  bcm2835gpio_trst_num 7
  bcm2835gpio_srst_num 18
   
  init
  targets
  reset halt
  
  t91samd bootloader 0
  program samd21_sam_ba.bin verify
  at91samd bootloader 8192
  reset
  shutdown

The GPIO pin numbers can be set here or in the raspberrypi2-native.cfg file. To do so change in:
  $ sudo nano /usr/local/share/openocd/scripts/interface/raspberrypi2-native.cfg
the following lines:
  bcm2835gpio_swd_nums 25 24
  bcm2835gpio_trst_num 7
  bcm2835gpio_srst_num 18

Connecting the SAMD21 Board:
   RasPi-GPIO  SAMD21
      18        Reset
      24        SWD IO
      25        SWD CLK
      GND       GND
      3V3       3V3

----

==== ... with a Segger J-Link Programmer ====
**UNDER CONSTRUCTION !**

and [[https://github.com/adafruit/Adafruit_Adalink|Adalink ARM CPU Tool]]\\

Download the software from:\\
[[https://www.segger.com/downloads/jlink/]]\\

Install OpenOCP\\

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==== Bootloader ====
Here one finds some SAMD21 bootloader:\\

[[https://github.com/arduino/ArduinoCore-samd/tree/master/bootloaders/zero|Arduino Zero Bootloader]]\\

[[https://github.com/arduino/ArduinoCore-samd/tree/master/bootloaders/mkrzero|Arduino MKR ZERO]]\\

[[https://github.com/Seeed-Studio/ArduinoCore-samd/blob/master/bootloaders/XIAOM0/update-bootloader-XIAO_m0-v3.7.0-33-g90ff611-dirty.bin|Seeeduino XIAO Bootloader]]\\
This bootloader bever worked for me!\\

----
==== Acknowledge ====

[[https://learn.adafruit.com/programming-microcontrollers-using-openocd-on-raspberry-pi/compiling-openocd|Programming Microcontrollers using OpenOCD on a Raspberry Pi by Lady Ada]]\\

[[https://embeddedcomputing.weebly.com/seeeduino-xiao-m0.html|Seeeduino Xiao M0​ by Embedded Computing]]\\

[[https://forum.seeedstudio.com/t/how-to-unbrick-a-dead-xiao-using-raspberry-pi-guide-openocd/253990|How to Unbrick a Dead XIAO Using Raspberry Pi by John Doe]]\\

[[http://openocd.org/doc/html/Flash-Commands.html|OpenOCD - Flash Commands]]\\

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