Getting started with ATSAME70 and Forth

This $10 board is very compelling with a 300MHz Cortex M7 and high speed USB out of the box, a feature not easily seen in other cheap MCUs:

https://www.aliexpress.com/item/1005003173783268.html

Nevertheless, getting it to run took me quite some time, and I want to share how to get going programming the board.

Setting up the programming environment

Getting a CMSIS-DAP probe

The board is best programmed with a CMSIS-DAP probe. The quickest way to get a CMSIS-DAP probe is to flash this firmware onto one of the cheap, ubiquitios STM32F103c8t6 boards (also known as the 'Blue Pill'):

F103-DAP-SWO-CDC-BLUEPILL-SWD_REMAP.hex

The same repository also contains ready-made firmware for the cheap STLINK clones available. Of course, you also can buy a ready-made CMSIS DAP probe for about $12 on AliExpress, but the BluePill will cost significantly less.

installing and setting up pyocd

Next we need an On-Chip-Debugger software. The easiest to use is pyocd, which you install with:

pip3 install pyocd

After installation you already should be able to see your CMSIS-DAP probe:

$ pyocd list
  #   Probe                        Unique ID
-------------------------------------------------
  0   CMSIS-DAP by ARM CMSIS-DAP   0001A0000000

After connecting the four wires (3.3V, SWDCLK, SWDIO, GND) from the BluePill to the target board you actually already can start using the probe:

$ pyocd commander
0000793:WARNING:board:Generic 'cortex_m' target type is selected by default; is this intentional?
You will be able to debug most devices, but not program  flash.
To set the target type use the '--target' argument or 'target_override' option.
Use 'pyocd list --targets' to see available targets types.

Connected to CoreSightTarget [Running]: 0001A0000000
pyocd> show graph
- <pyocd.board.board.Board object at 0x7faf9b5717f0>
  - <pyocd.coresight.coresight_target.CoreSightTarget object at 0x7faf9b571850>
    - <pyocd.coresight.cortex_m.CortexM object at 0x7faf98c045e0>
      - <pyocd.coresight.dwt.DWT object at 0x7faf98c04670>
      - <pyocd.coresight.fpb.FPB object at 0x7faf98c047f0>
      - <pyocd.coresight.itm.ITM object at 0x7faf98c2b2e0>
      - <pyocd.coresight.tpiu.TPIU object at 0x7faf98c04160>

pyocd> show target
Target:       CoreSightTarget
DAP IDCODE:   0x0bd11477

As the warning message suggests, you actually can already start looking around in the memories of the target, and can even run a debug server, but without complete target support you cannot:

• flash and erase the device
• set breakpoints and full debugger features

To accomplish this, we need to download the device support pack, which you can download from the Microchip CMSIS packs download site, searching for SAME70 and scrolling down to the device entry.

I created a directory for downloaded CMSIS-packs in /opt, where I saved the downloaded pack:

$ ls /opt/cmsis-packs
Atmel.SAME70_DFP.2.4.166.atpack

This pack is actually a zip file and also contains complete board support for C/C++ (Header files, example code, linker scripts, SVD-files and pyocd plugin).

As soon you have the pack available, you can use it in pyocd:

$ pyocd commander  --pack /opt/cmsis-packs/Atmel.SAME70_DFP.2.4.166.atpack --target atsame70n19
Connected to ATSAME70N19 [Running]: 0001A0000000
pyocd> show target
Target:       ATSAME70N19
DAP IDCODE:   0x0bd11477
pyocd> show graph
- <pyocd.board.board.Board object at 0x7f37350e7760>
  - <pyocd.target.pack.pack_target.ATSAME70N19 object at 0x7f3732513df0>
    - <pyocd.coresight.cortex_m.CortexM object at 0x7f37323691c0>
      - <pyocd.coresight.dwt.DWT object at 0x7f3730246e50>
      - <pyocd.coresight.fpb.FPB object at 0x7f3732369160>
      - <pyocd.coresight.itm.ITM object at 0x7f37303f12e0>
      - <pyocd.coresight.tpiu.TPIU object at 0x7f3732370ac0>
pyocd> show map
 Region  Type   Start       End         Size        Access  Sector      Page
 IROM1   Flash  0x00400000  0x0047ffff  0x00080000  rx      0x00002000  0x00000200
 IROM2   Rom    0x00800000  0x00803fff  0x00004000  rx      -           -
 IRAM1   Ram    0x20400000  0x2043ffff  0x00040000  rwx     -           -

Now the debug probe can do anything we need to, including erasing, flashing, debugging, setting breakpoints, etc. We are ready to go.

As this gets tedious easily, you can create a pyocd.yaml file in the same directory of the firmware you like to flash. In our case this is located in: mecrisp-stellaris-source/atsame70-ra/pyocd.yaml:

probes:
  0001A0000000:
    target_override:  atsame70n19
    test_binary:      mecrisp-stellaris-atsame70n19.bin

pack:
  - /opt/cmsis-packs/Atmel.SAME70_DFP.2.4.166.atpack

building and flashing mecrisp FORTH onto the target

As now everything is set up and ready, we build the firmware:

$ make
arm-none-eabi-as -g mecrisp-stellaris-atsame70n19.s -o mecrisp-stellaris-atsame70n19.o
arm-none-eabi-ld -g -o mecrisp-stellaris-atsame70n19.elf -T memmap mecrisp-stellaris-atsame70n19.o
arm-none-eabi-objdump -D mecrisp-stellaris-atsame70n19.elf > mecrisp-stellaris-atsame70n19.list
arm-none-eabi-objcopy mecrisp-stellaris-atsame70n19.elf mecrisp-stellaris-atsame70n19.bin -O binary
arm-none-eabi-objdump --source --all-headers --demangle --line-numbers --wide mecrisp-stellaris-atsame70n19.elf > mecrisp-stellaris-atsame70n19.lst
arm-none-eabi-objcopy -I binary -O ihex mecrisp-stellaris-atsame70n19.bin mecrisp-stellaris-atsame70n19.hex

$ pyocd erase --chip
0001266:INFO:eraser:Erasing chip...
0003265:INFO:eraser:Done

$ pyocd flash mecrisp-stellaris-atsame70n19.elf
[====================] 100%
0003918:INFO:loader:Erased 24576 bytes (3 sectors), programmed 24576 bytes (48 pages), skipped 0 bytes (0 pages) at 9.35 kB/s

The chip erase above would strictly have been necessary, because, as you can see the flash command does the erase automatically. It is, however, a nice way to get a clean slate if the MCU got messed up somehow.

Then mecrisp FORTH is ready to use:

$ picocom -b 500000 /dev/ttyUSB0 --imap lfcrlf,crcrlf --omap delbs,crlf --send-cmd "ascii-xfr -s -l 80 -n"
picocom v3.1

port is        : /dev/ttyUSB0
flowcontrol    : none
baudrate is    : 500000
parity is      : none
databits are   : 8
stopbits are   : 1
escape is      : C-a
local echo is  : no
noinit is      : no
noreset is     : no
hangup is      : no
nolock is      : no
send_cmd is    : ascii-xfr -s -l 80 -n
receive_cmd is : rz -vv -E
imap is        : crcrlf,lfcrlf,
omap is        : crlf,delbs,
emap is        : crcrlf,delbs,
logfile is     : none
initstring     : none
exit_after is  : not set
exit is        : no

Type [C-a] [C-h] to see available commands
Terminal ready
  ok.
  ok.
reset Mecrisp-Stellaris RA 2.5.9 for SAME70N19 by Matthias Koch

picocom is nice for getting started quickly, but it lacks support for forth files incluing other forth files. If you need that, e4thcom is recommended: https://wiki.forth-ev.de/doku.php/en:projects:e4thcom

This concludes the introduction.

Have fun!