P8 watch is one of many smartwatches supported by DaFit app (including PineTime). It is quite cheap (~$17 USD on aliexpress) and has full touchscreen, button and 240x240 color display.
Fortunately DaFit designers decided to not to use Nordic secure DFU bootloader and implemented their own with no fw signing via private keys :-) So thanks to atc1441's reverse engineering efforts (video, DaFlasher, github) we now have easy way to update many of these watches without taking apart!
Also it looks like the hw/sw design of all those watches is very similar:
- 4MB SPI memory (pinout: CLK=2,MOSI=3,MISO=4,CS=5) with images/fonts
- SoftDevice S132 5.0.0
- custom bootloader at 0x78000 that can update application from SPI flash
There are multiple ways to run your custom firmware:
- Directly upload you application built for Nordic SDK14 with Softdevice 5.0 as a bin file (by DaFlasher)
- probably not the option you want to start with as a beginner
- most advanced but most flexible option, 'easiest' way to restore to stock, best for backups of original state including bootloader and UICR area
- there is a size limit, app size can be 0x1000 to 0x2f000 (~185KB)
- to provide updates you must implement updating procedure yourself = accept new binary and store it to SPI flash and reboot to DaFit bootloader
- Upload atc1441's app that installs standard nordic DFU bootloader first and then make DFU packages for SDK14/SD5.0 via nrfutil
- easier update via nordic tools
- app can be larger (0x23000 to 0x78000)
- S132 5.0 = Bluetooth 5.0
- Upload also DFU package to upgrade/downgrade SoftDevice + DFU bootloader to move to other Nordic SDK
- SDK12 with Softdevice S132 3.0 is default for Espruino
- SDK11 with S132 2.0 is default for atc1441's Arduino (less bluetooth features but good enough and with most flash and RAM memory available)
For option 1. use espruino-xxx-DaFit.bin bin file and upload via DaFlasher. This allows you to backup what you want or
restore original firmware or update to DFU bootlader by hand. This build is not best for full Espruino experience since some features were disabled to fit the size limit so this is just to get you started to get access to the device with as few modifications as possible. Beware that this choice is for advanced users, you should know what you are doing. After possibly backing up DaFit original bootloader or UICR there are two ways how to get out of this limited espruino - 1. Fix bootloader setting in UICR to point to 0x7e000 and flash atc1441's/nordic bootloader (which moves you to state like in option 2 below). Fo that check first guide about replacig bootloader and then see prepared bootloader here. Beware that if you don't fix UICR bootloader settings value at 0x10001018 you will brick your device when later upgrading/downgrading bootloader or softdevice as described in the wiki (happened to me with DK08 watch). Another possibility how to get out of this limited espruino environment is to put something else to end of SPI flash, mark it for upgrade and reboot. Then original DaFit bootloader will replace espruino with new application you put there - possibly original dafit watch application. However while it is not hard to do and it worked for me there is currently no guide.
For option 2. first use DaFlasher + atc1441's bootloader .bin and then use espruino-xx-SDK14-SD50.zip package - again via
DaFlasher or Nordic DFU tools. For advanced way you can also use -DaFit.bin first to install bootloader yourself via Espruino code and then use this option.
For option 3. there is now SDK11 build if you downgrade via FitBootloaderDFU2.0.1.zip to SoftDevice 2.x
TODO - P8 espruino package for SDK12 with Espruino bootloader
You may check example/demo with display driver implemented as inline C. While it is a bit unusual to do it like this, it is fast, works and was fun to develop. You can get it here. There is 4bit/16color in memory framebuffer (taking 28KB out of total 64KB of RAM) and the palette transformation to 12bit display colors is done on the fly when sending data to the display between waiting for DMA transfers, there is no extra delay, everything is limited by slow 8Mbps SPI speed limit of nrf52832. For more free memory for the code you may reduce 'bpp' variable to 2 or 1 to have 4 or 2 color mode.
For more info about getting InlineC compiler running see https://github.com/fanoush/ds-d6/wiki/Espruino-Inline-C