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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](https://gitlab.cba.mit.edu/squidworks/moduleboard-atsamd51/), 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](https://gitlab.cba.mit.edu/pub/hello-world/tools/tree/master/openocd).
## 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](https://github.com/adafruit/asf4)), 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](https://forgge.github.io/theCore/guides/running-openocd-without-sudo.html) 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](https://gitlab.cba.mit.edu/squidworks/moduleboard-atsamd51/tree/master), the red and
green LEDs should blink.