Merge pull request #554 from keyboardio/hardware/ATMegaKeyboard/readCols-no-funroll

ATMegaKeyboard: Disable loop unrolling for readCols()
pull/555/head
Jesse Vincent 6 years ago committed by GitHub
commit 3d575345bb
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23

@ -129,6 +129,20 @@ bool ATMegaKeyboard::isKeyMasked(byte row, byte col) {
return bitRead(KeyboardHardware.masks_[row], col);
}
/*
* This function has loop unrolling disabled on purpose: we want to give the
* hardware enough time to produce stable PIN reads for us. If we unroll the
* loop, we will not have that, because even with the NOP, the codepath is too
* fast. If we don't have stable reads, then entire rows or columns will behave
* erratically.
*
* For this reason, we ask the compiler to not unroll our loop, which in turn,
* gives hardware enough time to produce stable reads, at the cost of a little
* bit of speed.
*
* Do not remove the attribute!
*/
__attribute__((optimize("no-unroll-loops")))
uint16_t ATMegaKeyboard::readCols() {
uint16_t results = 0x00 ;
for (uint8_t i = 0; i < KeyboardHardware.matrix_columns; i++) {

Loading…
Cancel
Save