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Verify CAN CRC (#333) #388

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Merged
azonenberg merged 3 commits into from
Dec 19, 2020
Merged

Verify CAN CRC (#333) #388

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b1ba421
initial support for CAN checksums
pd0wm Dec 19, 2020
c15bc13
fix formatting
pd0wm Dec 19, 2020
da5dd5a
add parentheses
pd0wm Dec 19, 2020
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22 changes: 20 additions & 2 deletions scopeprotocols/CANDecoder.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -126,6 +126,11 @@ void CANDecoder::Refresh()
int frame_bytes_left = 0;
int32_t frame_id = 0;
char tmp[128];

// CRC (http://esd.cs.ucr.edu/webres/can20.pdf page 13)
const uint16_t crc_poly = 0x4599;
uint16_t crc = 0;

for(size_t i = 0; i < len; i++)
{
bool v = diff->m_samples[i];
Expand Down Expand Up @@ -218,6 +223,16 @@ void CANDecoder::Refresh()
current_field |= 1;
nbit ++;

if (state != STATE_CRC){
uint16_t crc_bit_14 = (crc >> 14) & 0x1;
uint16_t crc_nxt = sampled_value ^ crc_bit_14;
crc = crc << 1;

if (crc_nxt){
crc = crc ^ crc_poly;
}
}

switch(state)
{
//Wait for at least 7 bit times low
Expand Down Expand Up @@ -245,6 +260,7 @@ void CANDecoder::Refresh()

tblockstart = off;
nbit = 0;
crc = 0;
current_field = 0;
state = STATE_ID;
break;
Expand Down Expand Up @@ -416,10 +432,12 @@ void CANDecoder::Refresh()
//CRC is 15 bits long
if(nbit == 15)
{
//TODO: actually check the CRC
bool crc_ok = (current_field == (crc & 0x7fff));
auto type = crc_ok ? CANSymbol::TYPE_CRC_OK : CANSymbol::TYPE_CRC_BAD;

cap->m_offsets.push_back(tblockstart);
cap->m_durations.push_back(end - tblockstart);
cap->m_samples.push_back(CANSymbol(CANSymbol::TYPE_CRC_OK, current_field));
cap->m_samples.push_back(CANSymbol(type, current_field));

state = STATE_CRC_DELIM;
}
Expand Down