yippee, i tested the PCB2 i put together yesterday, and successfully uploaded a test program to it, turning it into an example USB-HID "mouse" that generates events, wobbling the cursor back and forwards.
over the past few days i found someone who coincidentally maintains a branch with USB support for the exact STM32F model ARM Cortex M0 that i chose, and i got a working "usb hid" example up and running on a demo board i have, here ($EUR 10 retail. amazing).
yesterday i populated PCB2 with components, i had got the STM32F072 the wrong way round, burned one out! used the IR solderer to remove it and stuck a new one down, this time the right way round :) then, with a lot of fiddling i managed to get the right connections to reset and put it into "DFU" - device firmware upload - mode.
then i just uploaded the firmware tested previously on the demo board, and yay it worked.
so i will do a bit more firmware programming, there is the keyboard matrix to do, I2C interface for the touchpanel (converting to real USB-HID events), and also there is the SPI interface for the 480x320 LCD. testing the LCD and capacitive panel for the first time will be interesting.
l.