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former hardcoded signal properties (high, low) are now set dynamically by functionalists get_signalproperties(...)

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tharexde 2020-06-21 01:09:47 +02:00
commit 1a9ca5a1e3
1 changed files with 57 additions and 9 deletions
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66
armsrc/em4x50.c
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@ -91,6 +91,9 @@ static em4x50_tag_t tag = {
#define FPGA_TIMER_0 0
int gHigh = 0;
int gLow = 0;
// auxiliary functions
static void init_tag(void) {
@ -234,6 +237,45 @@ static void em4x50_setup_read(void) {
// functions for "reader" use case
static void get_signalproperties(void) {
// calculate signal properties (mean amplitudes) from measured data:
// 32 amplitudes (maximum values) -> mean amplitude value -> gHigh -> gLow
int no_periods = 32, pct = 75, noise = 140;
uint8_t sample = 0, sample_ref = 127;
uint8_t sample_max_mean = 0;
uint8_t sample_max[no_periods];
uint32_t sample_max_sum = 0;
// wait until signal/noise > 1
while (AT91C_BASE_SSC->SSC_RHR < noise);
// calculate mean maximum value of 32 periods, each period has a length of
// 3 single "full periods" to eliminate the influence of a listen window
for (int i = 0; i < no_periods; i++) {
AT91C_BASE_TC0->TC_CCR = AT91C_TC_SWTRG;
while (AT91C_BASE_TC0->TC_CV < T0 * 3 * EM4X50_T_TAG_FULL_PERIOD) {
sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
if (sample > sample_max[i])
sample_max[i] = sample;
}
sample_max_sum += sample_max[i];
}
sample_max_mean = sample_max_sum / no_periods;
// set global envelope variables
gHigh = sample_ref + pct * (sample_max_mean - sample_ref) / 100;
gLow = sample_ref - pct * (sample_max_mean - sample_ref) / 100;
}
static int get_next_bit(void) {
// returns bit value (or EM4X50_BIT_OTHER -> no bit pattern) by evaluating
@ -242,8 +284,6 @@ static int get_next_bit(void) {
// a listen window (return value = EM4X50_BIT_OTHER) in functions
// "find_double_listen_window" and "check_ack"
int dhigh = 230; // 90% of maximum sample value (255)
int dlow = 25; // 10% of maximum sample value (255)
uint8_t sample;
// get sample at 3/4 of bit period
@ -254,9 +294,9 @@ static int get_next_bit(void) {
wait_timer(0, T0 * EM4X50_T_TAG_QUARTER_PERIOD);
// decide wether "0" or "1"
if (sample > dhigh)
if (sample > gHigh)
return EM4X50_BIT_0;
else if (sample < dlow)
else if (sample < gLow)
return EM4X50_BIT_1;
return EM4X50_BIT_OTHER;
@ -266,19 +306,19 @@ static uint32_t get_pulse_length(void) {
// iterates pulse length (low -> high -> low)
uint8_t sample = 0, high = 192, low = 64;
uint8_t sample = 0;
sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
while (sample > low)
while (sample > gLow)
sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
AT91C_BASE_TC1->TC_CCR = AT91C_TC_SWTRG;
while (sample < high)
while (sample < gHigh)
sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
while (sample > low)
while (sample > gLow)
sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
return (uint32_t)AT91C_BASE_TC1->TC_CV;
@ -690,8 +730,10 @@ void em4x50_info(em4x50_data_t *etd) {
init_tag();
em4x50_setup_read();
// set gHigh and gLow
get_signalproperties();
if (etd->pwd_given) {
// try to login with given password
@ -802,6 +844,9 @@ void em4x50_write(em4x50_data_t *etd) {
init_tag();
em4x50_setup_read();
// set gHigh and gLow
get_signalproperties();
// reorder word according to datasheet
msb2lsb_word(etd->word);
@ -852,6 +897,9 @@ void em4x50_write_password(em4x50_data_t *etd) {
init_tag();
em4x50_setup_read();
// set gHigh and gLow
get_signalproperties();
// login and change password
if (login(etd->password)) {