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optimize parity calculations in SerialPIO (#2932) (#2933)

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use bit manipulation technique from http://www.graphics.stanford.edu/~seander/bithacks.html#ParityParallel for parity calculation

Co-authored-by: Ahmed ARIF <contact@eotics.com>
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Ahmed ARIF 2025-05-01 23:06:52 +02:00 committed by GitHub
parent 227d71ed18
commit 59614a99c8
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GPG key ID: B5690EEEBB952194
1 changed files with 8 additions and 11 deletions
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19
cores/rp2040/SerialPIO.cpp
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@ -68,13 +68,10 @@ static PIOProgram *_getRxProgram(int bits) {
}
// ------------------------------------------------------------------------
// TODO - this works, but there must be a faster/better way...
static int __not_in_flash_func(_parity)(int bits, int data) {
int p = 0;
for (int b = 0; b < bits; b++) {
p ^= (data & (1 << b)) ? 1 : 0;
}
return p;
static int __not_in_flash_func(_parity)(int data) {
data ^= data >> 4;
data &= 0xf;
return (0x6996 >> data) & 1;
}
// We need to cache generated SerialPIOs so we can add data to them from
@ -100,14 +97,14 @@ void __not_in_flash_func(SerialPIO::_handleIRQ)() {
uint32_t decode = _rxPIO->rxf[_rxSM];
uint32_t val = decode >> (32 - _rxBits - 1);
if (_parity == UART_PARITY_EVEN) {
int p = ::_parity(_bits, val);
int p = ::_parity(val);
int r = (val & (1 << _bits)) ? 1 : 0;
if (p != r) {
// TODO - parity error
continue;
}
} else if (_parity == UART_PARITY_ODD) {
int p = ::_parity(_bits, val);
int p = ::_parity(val);
int r = (val & (1 << _bits)) ? 1 : 0;
if (p == r) {
// TODO - parity error
@ -374,10 +371,10 @@ size_t SerialPIO::write(uint8_t c) {
if (_parity == UART_PARITY_NONE) {
val |= 7 << _bits; // Set 2 stop bits, the HW will only transmit the required number
} else if (_parity == UART_PARITY_EVEN) {
val |= ::_parity(_bits, c) << _bits;
val |= ::_parity(c) << _bits;
val |= 7 << (_bits + 1);
} else {
val |= (1 ^ ::_parity(_bits, c)) << _bits;
val |= (1 ^ ::_parity(c)) << _bits;
val |= 7 << (_bits + 1);
}
val <<= 1; // Start bit = low