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AP_Math: added xmodem CRC 

used by blheli 4-way ESC protocol
This commit is contained in:
Andrew Tridgell 2018-03-18 16:01:27 +11:00
parent 2933d4dd35
commit 17f2f40b11
2 changed files with 31 additions and 0 deletions
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28
libraries/AP_Math/crc.cpp
View File

@ -59,3 +59,31 @@ uint8_t crc_crc8(const uint8_t *p, uint8_t len)
return crc & 0xFF;
}
/*
xmodem CRC thanks to avr-liberty
https://github.com/dreamiurg/avr-liberty
*/
uint16_t crc_xmodem_update(uint16_t crc, uint8_t data)
{
crc = crc ^ ((uint16_t)data << 8);
for (uint16_t i=0; i<8; i++)
{
if(crc & 0x8000) {
crc = (crc << 1) ^ 0x1021;
} else {
crc <<= 1;
}
}
return crc;
}
uint16_t crc_xmodem(const uint8_t *data, uint16_t len)
{
uint16_t crc = 0;
for (uint16_t i=0; i<len; i++) {
crc = crc_xmodem_update(crc, data[i]);
}
return crc;
}

3
libraries/AP_Math/crc.h
View File

@ -17,4 +17,7 @@
*/
uint8_t crc_crc8(const uint8_t *p, uint8_t len);
uint16_t crc_xmodem_update(uint16_t crc, uint8_t data);
uint16_t crc_xmodem(const uint8_t *b, uint16_t len);