If it gets this far, the firmware is at least sort of running, so the
watchdog has served its purpose of resetting to the bootloader if
there's invalid firmware flashed to the device.
Provide the basic functionality for setting direction, turning on and
off, toggling, reading inputs, and enabling/disabling pullups.
This chip also provides pulldowns, so in the future I will also
implement pulldown control so we can detect shorts to 5V.
SPI isn't needed on this platform because we don't need an I/O expander.
So this can be a bunch of stub functions that do nothing. They will be
optimized out during the linking process anyway.
This implements a USB CDC serial port using the Nuvoton USBD driver. The
USB handling is based on Nuvoton's BSP sample code, especially the IRQ
handlers and descriptor buffer configuration. The descriptors have been
adapted to be similar to the AVR version, and RX/TX functions have been
written to implement an API closer to LUFA, which is what the SIMM
programmer common code needs.
I'm sure it's slightly more efficient as a static inline function, but
it results in less flash usage as a separate function. This is important
for the bootloader where every byte matters.
Nuvoton's sample startup_M251.S file handles enough initialization for
my purposes, so I can completely bypass _start and jump directly to
main. Note that I also had to add a define to enable clearing of BSS.
The default values for SystemCoreClock, CyclesPerUs, and PllClock work
fine for my purposes of running from the 48 MHz HIRC. Remove unnecessary
initialization code. This is especially useful for the bootloader where
flash space is at a premium.
Also strip out unneeded UART setup code.
This will be used during firmware updates so that the main firmware can
communicate to the bootloader that it should stay in the bootloader for
a firmware update rather than run the main firmware again.
Doug Brown