94 lines
3.8 KiB
Markdown
94 lines
3.8 KiB
Markdown
# Developers on Coldcard
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Yes, external developers can modify Coldcard... We've saved 128k of flash just for you!
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## Approaches
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### Hard Core
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- build a new image, all the way to a DFU file (see `../stm32/Makefile`)
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- sign with non-production key, provided in github tree
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- install your DFU file using existing upgrade methods (microSD, usb upload)
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- you can replace any part of the python code, and even the mpy interpreter itself
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- you cannot change the bootrom, and it still runs first
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- your code will not be signed by the factory key, so warning and delay, is shown:
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- to get green light, the user (who knows the main PIN) must do the "bless" operation
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- you can distrubute your DFU file to the world
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- you can take factory-fresh Coldcards, destroy the tamper-evident bag, and load your
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firmware onto them before shipping to your customers.
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### Medium Core
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- install any published dev version (or build your own, see above)
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- enable the virtual disk feature:
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Advanced > Danger Zone > I Am Developer. > Enable USB Disk
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- REPL and mass-storage emulation will now be active
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- or you can just enable the REPL, and connect there and experiment first
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- expect to find helpful file: `/Volumes/COLDCARD/README.txt`
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- write code and save into `.../COLDCARD/lib`
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- any same-named file will replace built-in stock module
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- `lib/boot2.py` and `lib/main2.py` are loaded if they exist during boot sequence
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- the only python you cannot override is `main.py`
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- RAM limits complexity of the override you can do (but freezing your micropython helps)
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- you cannot change the bootrom, and it still runs first
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- changes to the virtual disk cause the light to go red, you'll need to bless after
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each change you make.
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- distribute your version by capturing an image of your working virtual disk drive,
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and then putting just that into a DFU file (128k)
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- users will have to have a similar dev version of main firmware, but
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you would probably give it to them, as separate DFU file.
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- both files could be put into a single DFU, but that's not supported by
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MicroSD upgrade method
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### Soft Core
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- Send an email to support asking for your altcoin to be supported. Await reply patiently.
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## Shortcuts and Accerations
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- You can enable USB, or USB disk emulation, automatically at the end of `boot2.py`.
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Mount the emulated disk, and create this file, as `/Volumes/COLDCARD/lib/boot2.py`
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```python
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# start the REPL very early
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import uasyncio.core as asyncio
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from usb import enable_usb
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loop = asyncio.get_event_loop()
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enable_usb(loop, True)
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```
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- To skip the prompts for the PIN, assuming correct PIN is '12-12'... add this code
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to `boot2.py` or run once when the system hasn't yet logged in.
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```python
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from main import settings
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settings.set('_skip_pin', '12-12')
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```
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- For max crash-change-rerun speed, enable the mass storage all the
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time, and work directly in `/COLDCARD/lib` files. After making a
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change, you just need to do a warm reboot (^D in REPL, 'warm reset'
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on menus). At that point, `main.py` runs, and your code will be
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used again. The USB doesn't disconnect, and the drive will still
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be mounted, ready for more changes.
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## Limitations
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- You cannot enable mass storage, virtual comm port (VCP = REPL access) and also HID
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for the Coldcard protocol at the same time. Pick any two.
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- `.py` files in `/lib` will be interpreted at runtime. This is slow, and bytecode
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takes large amounts of RAM. Some files in the normal code are too big to even
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fit in RAM. The solution is to freeze your code before copying onto Coldcard. See the
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`stm32/Makefile` target `up` which does a build (freezing all the files, using
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`mpy-cross`) and then rsyncs the changed `.mpy` files into place. You'll want to do
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this on a smaller scale, and probably only for the files you are working on.
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