xobs/bpsk-demod
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

demod: make nco generation self-contained

Browse Source 
Signed-off-by: Sean Cross <sean@xobs.io>
This commit is contained in:
Sean Cross 2020-06-10 17:14:44 +08:00
parent 8cc5028bd9
commit 1e22ca7b2e
1 changed files with 22 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
src/bpsk/demod.c
View File

@ -24,6 +24,8 @@ struct nco_state
float32_t freq; // Hz float32_t freq; // Hz
float32_t phase; // rad float32_t phase; // rad
float32_t offset;
float32_t error;
}; };
struct bpsk_state struct bpsk_state
@ -42,7 +44,6 @@ struct bpsk_state
float32_t fir_state[SAMPLES_PER_PERIOD + FIR_STAGES - 1]; float32_t fir_state[SAMPLES_PER_PERIOD + FIR_STAGES - 1];
struct nco_state nco; struct nco_state nco;
float32_t nco_error;
arm_fir_instance_f32 i_lpf; arm_fir_instance_f32 i_lpf;
float32_t i_lpf_state[SAMPLES_PER_PERIOD + LPF_STAGES - 1]; float32_t i_lpf_state[SAMPLES_PER_PERIOD + LPF_STAGES - 1];
@ -72,22 +73,28 @@ static void print_char(uint32_t c)
printf("%c", varcode_to_char(c >> 2)); printf("%c", varcode_to_char(c >> 2));
} }
static void nco(float32_t control, uint32_t timestep, float32_t *i, static void make_nco(float32_t *i, float32_t *q)
float32_t *q)
{ {
// control is a number from +1 to -1, which translates to -pi to +pi // control is a number from +1 to -1, which translates to -pi to +pi
// additional phase per time step timestep is the current time step, // additional phase per time step timestep is the current time step,
// expressed in terms of samples since t=0 i is a pointer to the in-phase // expressed in terms of samples since t=0 i is a pointer to the in-phase
// return value q is a pointer to the quadrature return value // return value q is a pointer to the quadrature return value
bpsk_state.nco.phase += (control / PI); float32_t timestep = bpsk_state.nco.offset;
while (timestep < SAMPLES_PER_PERIOD + bpsk_state.nco.offset)
{
bpsk_state.nco.phase += (bpsk_state.nco.error / PI);
*i++ = arm_cos_f32((timestep * bpsk_state.nco.freq * 2 * PI) /
bpsk_state.nco.samplerate +
bpsk_state.nco.phase);
*q++ = arm_sin_f32((timestep * bpsk_state.nco.freq * 2 * PI) /
bpsk_state.nco.samplerate +
bpsk_state.nco.phase);
timestep += 1;
}
*i = arm_cos_f32((((float32_t)timestep) * bpsk_state.nco.freq * 2 * PI) / // XXX MAKE SURE TO DEAL WITH TIMESTEP WRPAPING
bpsk_state.nco.samplerate + bpsk_state.nco.offset = timestep;
bpsk_state.nco.phase);
*q = arm_sin_f32((((float32_t)timestep) * bpsk_state.nco.freq * 2 * PI) /
bpsk_state.nco.samplerate +
bpsk_state.nco.phase);
} }
void bpsk_demod_init(void) void bpsk_demod_init(void)
@ -98,7 +105,8 @@ void bpsk_demod_init(void)
bpsk_state.nco.samplerate = SAMPLE_RATE; bpsk_state.nco.samplerate = SAMPLE_RATE;
bpsk_state.nco.freq = CARRIER_TONE; bpsk_state.nco.freq = CARRIER_TONE;
bpsk_state.nco.phase = 0.0; bpsk_state.nco.phase = 0.0;
bpsk_state.nco_error = 0.0; bpsk_state.nco.error = 0.0;
bpsk_state.nco.offset = 0;
bpsk_state.agc = 1.0; bpsk_state.agc = 1.0;
bpsk_state.agc_step = 0.05; bpsk_state.agc_step = 0.05;
@ -257,12 +265,7 @@ static void bpsk_core(void)
// current timestamp. // current timestamp.
float32_t i_samps[SAMPLES_PER_PERIOD]; float32_t i_samps[SAMPLES_PER_PERIOD];
float32_t q_samps[SAMPLES_PER_PERIOD]; float32_t q_samps[SAMPLES_PER_PERIOD];
static int nco_offset = 0; make_nco(i_samps, q_samps);
for (unsigned int i = 0; i < SAMPLES_PER_PERIOD; i++)
{
nco(bpsk_state.nco_error, i + nco_offset, &(i_samps[i]), &(q_samps[i]));
}
nco_offset += SAMPLES_PER_PERIOD;
static float32_t i_mult_samps[SAMPLES_PER_PERIOD]; static float32_t i_mult_samps[SAMPLES_PER_PERIOD];
static float32_t q_mult_samps[SAMPLES_PER_PERIOD]; static float32_t q_mult_samps[SAMPLES_PER_PERIOD];
@ -289,8 +292,8 @@ static void bpsk_core(void)
avg += errorwindow[i]; avg += errorwindow[i];
} }
avg /= ((float32_t)SAMPLES_PER_PERIOD); avg /= ((float32_t)SAMPLES_PER_PERIOD);
bpsk_state.nco_error = -(avg); bpsk_state.nco.error = -(avg);
// printf("err: %0.04f\n", bpsk_state.nco_error); // printf("err: %0.04f\n", bpsk_state.nco.error);
} }
int bpsk_demod(int *bit, demod_sample_t *samples, uint32_t nb, uint32_t *processed_samples) int bpsk_demod(int *bit, demod_sample_t *samples, uint32_t nb, uint32_t *processed_samples)