Merge pull request #86 from bgamari/master

sched: Mark asm! uses as volatile

Reviewed-by: farcaller
stm32f4: Update GPIODirection usage
stm32f4: Fix uint casts
stm32f4: Fix abort usages
Merge pull request #88 from bgamari/stm32-fixes

STM32F4 fixes

Reviewed-by: farcaller
ioreg: Initial commit