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Reduce the number of bytes over SPI for MCP2515Class::parsePacket() by up to 2.8x #46

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Reduce the number of bytes over SPI for MCP2515Class::parsePacket() by up to 2.8x #46

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57 changes: 41 additions & 16 deletions src/MCP2515.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -212,49 +212,74 @@ int MCP2515Class::endPacket()

int MCP2515Class::parsePacket()
{
int n;

uint8_t intf = readRegister(REG_CANINTF);
SPI.beginTransaction(_spiSettings);
digitalWrite(_csPin, LOW);
SPI.transfer(0xb0); // RX STATUS
uint8_t rxStatus = SPI.transfer(0x00);
digitalWrite(_csPin, HIGH);
SPI.endTransaction();

if (intf & FLAG_RXnIF(0)) {
int n;
if (rxStatus & 0x40) {
n = 0;
} else if (intf & FLAG_RXnIF(1)) {
} else if (rxStatus & 0x80) {
n = 1;
} else {
_rxId = -1;
_rxExtended = false;
_rxRtr = false;
_rxDlc = 0;
_rxIndex = 0;
_rxLength = 0;
return 0;
}

_rxExtended = (readRegister(REG_RXBnSIDL(n)) & FLAG_IDE) ? true : false;

uint32_t idA = ((readRegister(REG_RXBnSIDH(n)) << 3) & 0x07f8) | ((readRegister(REG_RXBnSIDL(n)) >> 5) & 0x07);
SPI.beginTransaction(_spiSettings);
digitalWrite(_csPin, LOW);
// Send READ RX BUFFER instruction to sequentially read registers, starting
// from RXBnSIDH(n).
SPI.transfer(0b10010000 | (n * 0x04));
uint8_t regSIDH = SPI.transfer(0x00);
uint8_t regSIDL = SPI.transfer(0x00);
_rxExtended = (regSIDL & FLAG_IDE) ? true : false;

// We could just skip the extended registers for standard frames, but that
// would actually add more overhead, and increase complexity.
uint8_t regEID8 = SPI.transfer(0x00);
uint8_t regEID0 = SPI.transfer(0x00);
uint8_t regDLC = SPI.transfer(0x00);
uint32_t idA = (regSIDH << 3) | (regSIDL >> 5);
if (_rxExtended) {
uint32_t idB = (((uint32_t)(readRegister(REG_RXBnSIDL(n)) & 0x03) << 16) & 0x30000) | ((readRegister(REG_RXBnEID8(n)) << 8) & 0xff00) | readRegister(REG_RXBnEID0(n));
uint32_t idB =
((uint32_t)(regSIDL & 0x03) << 16)
| ((uint32_t)regEID8 << 8)
| regEID0;

_rxId = (idA << 18) | idB;
_rxRtr = (readRegister(REG_RXBnDLC(n)) & FLAG_RTR) ? true : false;
_rxRtr = (regDLC & FLAG_RTR) ? true : false;
} else {
_rxId = idA;
_rxRtr = (readRegister(REG_RXBnSIDL(n)) & FLAG_SRR) ? true : false;
_rxRtr = (regSIDL & FLAG_SRR) ? true : false;
}
_rxDlc = readRegister(REG_RXBnDLC(n)) & 0x0f;

_rxDlc = regDLC & 0x0f;
_rxIndex = 0;

if (_rxRtr) {
_rxLength = 0;
} else {
_rxLength = _rxDlc;

for (int i = 0; i < _rxLength; i++) {
_rxData[i] = readRegister(REG_RXBnD0(n) + i);
// Get the data.
for (uint8_t i = 0; i < _rxLength; i++) {
_rxData[i] = SPI.transfer(0x00);
}
}

modifyRegister(REG_CANINTF, FLAG_RXnIF(n), 0x00);

// Don't need to unset the RXnIF(n) flag as this is done automatically when
// setting the CS high after a READ RX BUFFER instruction.
digitalWrite(_csPin, HIGH);
SPI.endTransaction();
return _rxDlc;
}

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