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Fix bug with manchester receive function. Using suggested algorithm from em4x70 datasheet

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This commit is contained in:
Christian Molson 2020-12-07 11:18:00 -05:00
parent 4e592eba1c
commit b0ff0ed526
1 changed files with 27 additions and 33 deletions
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60
armsrc/em4x70.c
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@ -488,12 +488,10 @@ static bool find_EM4X70_Tag(void) {
static int em4x70_receive(uint8_t *bits) {
bool bbitchange = false;
uint32_t pl;
int bit_pos = 0;
uint8_t edge = 0;
// Set first bit to a 1 for starting off corectly
bits[0] = 1;
bool foundheader = false;
@ -529,48 +527,44 @@ static int em4x70_receive(uint8_t *bits) {
// between two listen windows only pulse lengths of 1, 1.5 and 2 are possible
while (true) {
bit_pos++;
pl = get_pulse_length();
if(edge)
pl = get_pulse_length();
else
pl = get_pulse_invert_length();
if (check_pulse_length(pl, EM4X70_T_TAG_FULL_PERIOD, EM4X70_T_TAG_QUARTER_PERIOD)) {
// pulse length = 1 -> keep former bit value
bits[bit_pos] = bits[bit_pos - 1];
// pulse length = 1
bits[bit_pos++] = edge;
} else if (check_pulse_length(pl, 3 * EM4X70_T_TAG_HALF_PERIOD, EM4X70_T_TAG_QUARTER_PERIOD)) {
// pulse length = 1.5 -> decision on bit change
if (bbitchange) {
// if number of pulse lengths with 1.5 periods is even -> add bit
bits[bit_pos] = (bits[bit_pos - 1] == 1) ? 1 : 0;
// pulse length of 1.5 changes bit value
bits[bit_pos + 1] = (bits[bit_pos] == 1) ? 0 : 1;
bit_pos++;
// next time add only one bit
bbitchange = false;
// pulse length = 1.5 -> flip edge detection
if(edge) {
bits[bit_pos++] = 0;
bits[bit_pos++] = 0;
edge = 0;
} else {
bits[bit_pos] = (bits[bit_pos - 1] == 1) ? 0 : 1;
// next time two bits have to be added
bbitchange = true;
bits[bit_pos++] = 1;
bits[bit_pos++] = 1;
edge = 1;
}
} else if (check_pulse_length(pl, 2 * EM4X70_T_TAG_FULL_PERIOD, EM4X70_T_TAG_QUARTER_PERIOD)) {
// pulse length of 2 means: adding 2 bits "01"
bits[bit_pos] = 0;
bits[bit_pos + 1] = 1;
bit_pos++;
// pulse length of 2
if(edge) {
bits[bit_pos++] = 0;
bits[bit_pos++] = 1;
} else {
bits[bit_pos++] = 1;
bits[bit_pos++] = 0;
}
} else if (check_pulse_length(pl, 3 * EM4X70_T_TAG_FULL_PERIOD, EM4X70_T_TAG_QUARTER_PERIOD)) {
// pulse length of 3 indicates listen window -> clear last
// bit (= 0) and return
} else if ( (edge && check_pulse_length(pl, 3 * EM4X70_T_TAG_FULL_PERIOD, EM4X70_T_TAG_QUARTER_PERIOD)) ||
(!edge && check_pulse_length(pl, 80, EM4X70_T_TAG_QUARTER_PERIOD))) {
// LIW detected (either invert or normal)
return --bit_pos;
}
}