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    Bare Metal Development

    This is a minimalist blink program. No bootloader, and no IDE to build things for us. Just the command line, a text editor, Makefiles, and a few open-source tools. You should use Linux to do this work; your mileage may vary on other operating systems.

    This example assumes you're using a squidworks module, but if you're using something else you'll just need to update which pins your LEDs are on.

    Setup

    We'll use OpenOCD to program our board. Relevant docs live here.

    Building

    Once that's done, clone this repo. Fire up your terminal, navigate to this directory, and run make. You should see something like this result:

    zach@crudite:~/Documents/atsamd51/baremetal$ make
Building file: main.c
ARM/GNU C Compiler
"arm-none-eabi-gcc" -x c -DDEBUG -Os -ffunction-sections -g3 -Wall -c -std=gnu99 -mthumb -mabi=aapcs-linux -mlong-calls -mcpu=cortex-m4 -mfloat-abi=softfp -mfpu=fpv4-sp-d16 -DSAMD51 -D__SAMD51J19A__ -I"samd51" -I"samd51/CMSIS/Include" -I"samd51/include" -I"samd51/startup" \
-MD -MP -MF "main.d" -MT"main.d" -MT"main.o"  -o "main.o" "main.c"
Finished building: main.c
Building file: samd51/startup/system_samd51.c
ARM/GNU C Compiler
"arm-none-eabi-gcc" -x c -DDEBUG -Os -ffunction-sections -g3 -Wall -c -std=gnu99 -mthumb -mabi=aapcs-linux -mlong-calls -mcpu=cortex-m4 -mfloat-abi=softfp -mfpu=fpv4-sp-d16 -DSAMD51 -D__SAMD51J19A__ -I"samd51" -I"samd51/CMSIS/Include" -I"samd51/include" -I"samd51/startup" \
-MD -MP -MF "samd51/startup/system_samd51.d" -MT"samd51/startup/system_samd51.d" -MT"samd51/startup/system_samd51.o"  -o "samd51/startup/system_samd51.o" "samd51/startup/system_samd51.c"
Finished building: samd51/startup/system_samd51.c
Building file: samd51/startup/startup_samd51.c
ARM/GNU C Compiler
"arm-none-eabi-gcc" -x c -DDEBUG -Os -ffunction-sections -g3 -Wall -c -std=gnu99 -mthumb -mabi=aapcs-linux -mlong-calls -mcpu=cortex-m4 -mfloat-abi=softfp -mfpu=fpv4-sp-d16 -DSAMD51 -D__SAMD51J19A__ -I"samd51" -I"samd51/CMSIS/Include" -I"samd51/include" -I"samd51/startup" \
-MD -MP -MF "samd51/startup/startup_samd51.d" -MT"samd51/startup/startup_samd51.d" -MT"samd51/startup/startup_samd51.o"  -o "samd51/startup/startup_samd51.o" "samd51/startup/startup_samd51.c"
Finished building: samd51/startup/startup_samd51.c
Building target: main.elf
Invoking: ARM/GNU Linker
"arm-none-eabi-gcc" -o main.elf main.o samd51/startup/system_samd51.o samd51/startup/startup_samd51.o  -Wl,--start-group -lm -Wl,--end-group -mthumb -mabi=aapcs-linux -mlong-calls -mcpu=cortex-m4 -mfloat-abi=softfp -mfpu=fpv4-sp-d16 -DSAMD51 \
-Wl,-Map="main.map" --specs=nano.specs -Wl,--gc-sections \
 \
 \
-T"samd51/startup/samd51j19a_flash.ld" \
-L"samd51/startup"
/usr/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/bin/ld: warning: main.o uses 32-bit enums yet the output is to use variable-size enums; use of enum values across objects may fail
/usr/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/bin/ld: warning: samd51/startup/system_samd51.o uses 32-bit enums yet the output is to use variable-size enums; use of enum values across objects may fail
/usr/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/bin/ld: warning: samd51/startup/startup_samd51.o uses 32-bit enums yet the output is to use variable-size enums; use of enum values across objects may fail
Finished building target: main.elf
"arm-none-eabi-objcopy" -O binary "main.elf" "main.bin"
"arm-none-eabi-objcopy" -O ihex -R .eeprom -R .fuse -R .lock -R .signature  \
        "main.elf" "main.hex"
"arm-none-eabi-objcopy" -j .eeprom --set-section-flags=.eeprom=alloc,load --change-section-lma \
        .eeprom=0 --no-change-warnings -O binary "main.elf" \
        "main.eep" || exit 0
"arm-none-eabi-objdump" -h -S "main.elf" > "main.lss"
"arm-none-eabi-size" "main.elf"
   text	   data	    bss	    dec	    hex	filename
    968	      0	  49184	  50152	   c3e8	main.elf
Deleting intermediate files...
rm -f main.o samd51/startup/system_samd51.o samd51/startup/startup_samd51.o
rm -f main.d samd51/startup/system_samd51.d samd51/startup/startup_samd51.d
rm -f main.a main.hex main.bin \
	main.lss main.eep main.map \
	main.srec

    Errors are not uncommon and are usually related to the directory structure of the Makefile. However, this repo includes all of the required SAMD51 libraries (from Atmel/Microchip's ASF4 framework, as shared by Adafruit), so if you grabbed the entire repo you should be fine. Post an issue if it doesn't work. Note one modification to the Makefile is that it deletes all the intermediate files (.o, .eep, etc) after producing the .elf file. If you want them, remove the lines in the Makefile after the phrase 'Deleting intermediate files...'.

    Programming

    Fourth, after you have your .elf file (in this case main.elf), connect an Atmel ICE programmer to your SAMD51 board and power it up. Note: make sure you use the correct pinout and the SAM port! Then run openocd. You should see the following:

    zach@crudite:~/Documents/atsamd51/baremetal$ openocd
Open On-Chip Debugger 0.10.0+dev-00409-g1ae106de-dirty (2019-10-14-20:41)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.org/doc/doxygen/bugs.html
none separate
adapter speed: 400 kHz
cortex_m reset_config sysresetreq
Info : Listening on port 6666 for tcl connections
Info : Listening on port 4444 for telnet connections
Info : CMSIS-DAP: SWD  Supported
Info : CMSIS-DAP: JTAG Supported
Info : CMSIS-DAP: Interface Initialised (SWD)
Info : CMSIS-DAP: FW Version = 1.0
Info : SWCLK/TCK = 1 SWDIO/TMS = 1 TDI = 1 TDO = 1 nTRST = 0 nRESET = 1
Info : CMSIS-DAP: Interface ready
Info : clock speed 400 kHz
Info : SWD DPIDR 0x2ba01477
Info : at91samd51j18.cpu: hardware has 6 breakpoints, 4 watchpoints
Info : Listening on port 3333 for gdb connections

    If you see Error: unable to open CMSIS-DAP device 0x3eb:0x2141, it probably means openocd needs root privileges to access the programmer. You could run sudo openocd, but a better solution is to follow the instructions here to create a new rule. Don't forget to restart udev after doing this with sudo udevadm trigger.

    Fifth, now that openocd is running, open a second terminal window and type gdb-multiarch main.elf (if you're using an older gdb version, it's arm-none-eabi-gdb main.elf). When gdb opens, type tar ext :3333 (a shortcut for target extended-remote :3333), then load. This should flash the microcontroller with the new code, at which point you can exit gdb with quit and y. In the openocd window, close the connection with Ctrl-C. If you're flashing one of Jake's moduleboards, the red and green LEDs should blink.