- Implement advanced LED flash support
- Tweak HAL_SPI_TransmitReceive to tolerate a longer SysTick interrupt
- Tune KEYBOARD_BOTDETECT parameters
- L-shift and R-shift are now high-speed alphanumeric keys
So apparently the STM32F401's SPI DMA is even more buggy than the 405's.
Worked around an intermittent stall/timeout by busy-waiting Upstream's
packet length transmission and reception, instead of DMA-ing it like the
packet body. Ugh...
SPI peripheral library. At this speed SPI requires ~60% CPU time at -Og
optimisation level. This could be further improved by trimming down the
SPI interrupt. But...
Speed is now limited by Downstream's single-packet-per-URB restriction,
to about 460kB/s. USB Middleware does not implement TX FIFO empty
interrupt, so a bit of work is required here.
Although I am not entirely convinced this is necessary, as the SPI data
stall issue only appeared with optimisation off (-O0). Perhaps re-visit
this if Upstream needs more free CPU time later...