So I can run my own bootloader code on the Blank Arrow eWallet-based development platform.
But I can't use a debugger on them.
So, I need a different solution.
I found the CorexxR dev board from Waveshare. Its a breakout board for the MCU that the Trezor uses, and also has the basic circuits required to get the chip running - USB, power circuits, a crystal, and breakouts for all the pins on the chip.
The problem is that the MCU on the Core205R is the STM32F205RBT, which has 128k of flash. The Trezor's STM32F205RET has 512k.
I read the specifications, and found that all the STM32F205 chips are pin-compatable, so Waveshare could just solder down a equivalent part that has more flash, then I'd be happy.
So I emailed them and asked if they could do this for me. They said they could -- if I ordered at least 50.
These have STM32F305RGT6 MCUs, with 1024k of flash.