merged in example USB CDC + HID code, but removed any comms with actual USART peripheral.
this code is not yet tested. once tested and USB enumerates, work can proceed.
jumper 1 will set LEDs to a dimmer level.
jumper 2 will disable LEDs entirely.
jumper 3 will turn the addon and USB ports on and off depending on ambient light level. the levels decided are arbitrary and may be updated with further testing.
fixed some initial GPIO configuration.
fixed systick interrupt not defined as an interrupt.
fixed any interactions with backup registers causing lockups.
completed RGBLED work.
fixed button handler code.
add currently non-working lightsense code.
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