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sdr_sxceiver: add DC offset correction support
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The samples are now split into blocks. The offset is corrected on
each block before it is given to SoapySX for transmission or
corrected after reception of a block from SoapySX. This ensures
there are no huge spikes in CPU usage and therefore delays when a
lot of samples should be transferred at once.
This commit is contained in:
Thomas Kolb 2025-10-26 19:05:34 +00:00
commit 052f5d4612
2 changed files with 77 additions and 16 deletions
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10
impl/src/config.h.template
View file

@ -70,4 +70,14 @@
#define SDR_GAIN_RX_LNA 30.0f // RF variable gain amplifier.
#define SDR_GAIN_RX_VGA 24.0f // Baseband variable gain amplifier.
// Offset compensation (these values will be subtracted from all samples).
// These generally depend on the gain settings above and need to be adjusted
// when the gain is changed.
#define SDR_TX_OFFSET_I 0.000000f
#define SDR_TX_OFFSET_Q 0.000000f
#define SDR_RX_OFFSET_I 0.000000f
#define SDR_RX_OFFSET_Q 0.000000f
#endif // CONFIG_H

83
impl/src/sdr/sdr_sxceiver.c
View file

@ -198,7 +198,7 @@ result_t sdr_init(sdr_ctx_t *ctx)
// set up and start RX
// set gains
if(SoapySDRDevice_setGainElement(ctx->sdr, SOAPY_SDR_RX, 0, "PGA", SDR_GAIN_RX_PGA) != 0) {
/*if(SoapySDRDevice_setGainElement(ctx->sdr, SOAPY_SDR_RX, 0, "PGA", SDR_GAIN_RX_PGA) != 0) {
LOG(LVL_ERR, "setGainElement fail: %s", SoapySDRDevice_lastError());
return ERR_SOAPY;
}
@ -206,6 +206,11 @@ result_t sdr_init(sdr_ctx_t *ctx)
if(SoapySDRDevice_setGainElement(ctx->sdr, SOAPY_SDR_RX, 0, "LNA", SDR_GAIN_RX_LNA) != 0) {
LOG(LVL_ERR, "setGainElement fail: %s", SoapySDRDevice_lastError());
return ERR_SOAPY;
}*/
if(SoapySDRDevice_setGain(ctx->sdr, SOAPY_SDR_RX, 0, SDR_GAIN_RX) != 0) {
LOG(LVL_ERR, "setGain fail: %s", SoapySDRDevice_lastError());
return ERR_SOAPY;
}
if(SoapySDRDevice_activateStream(ctx->sdr, ctx->rx_stream, 0, 0, 0) != 0) {
@ -292,15 +297,38 @@ result_t sdr_transmit(sdr_ctx_t *ctx, const float complex *samples, size_t nsamp
flags |= SOAPY_SDR_HAS_TIME;
}
void *buffs[] = {(void*)(samples)};
const size_t BLOCK_SIZE = 4096;
float complex tx_block[BLOCK_SIZE];
int ret = SoapySDRDevice_writeStream(ctx->sdr, ctx->tx_stream, (const void* const*)buffs, nsamples, &flags, time_ns, timeout_us);
size_t samples_transmitted = 0;
if(ret <= 0) {
LOG(LVL_ERR, "writeStream fail: %s", SoapySDRDevice_lastError());
return ERR_SOAPY;
} else if(ret != nsamples) {
LOG(LVL_WARN, "writeStream() did not transmit all samples: %i/%zu", ret, nsamples);
while(samples_transmitted < nsamples) {
size_t samples_remaining = nsamples - samples_transmitted;
size_t block_samples = BLOCK_SIZE;
if(samples_remaining < BLOCK_SIZE) {
block_samples = samples_remaining;
}
const float complex *block_start = samples + samples_transmitted;
for(size_t i = 0; i < block_samples; i++) {
tx_block[i] = block_start[i] - (SDR_TX_OFFSET_I + I * SDR_TX_OFFSET_Q);
}
void *buffs[] = {(void*)(tx_block)};
int64_t block_time = time_ns + samples_transmitted * 1000000000LL / SDR_TX_SAMPLING_RATE;
int ret = SoapySDRDevice_writeStream(ctx->sdr, ctx->tx_stream, (const void* const*)buffs, block_samples, &flags, block_time, timeout_us);
if(ret <= 0) {
LOG(LVL_ERR, "writeStream fail: %s", SoapySDRDevice_lastError());
return ERR_SOAPY;
} else if((size_t)ret != block_samples) {
LOG(LVL_WARN, "writeStream() did not transmit all samples: %i/%zu", ret, block_samples);
}
samples_transmitted += ret;
}
return OK;
@ -313,18 +341,41 @@ result_t sdr_receive(sdr_ctx_t *ctx, float complex *samples, size_t *nsamples, l
return ERR_INVALID_STATE;
}
void *buffs[] = {(void*)samples};
const size_t BLOCK_SIZE = 4096;
float complex rx_block[BLOCK_SIZE];
long long timeNs;
int flags;
int ret = SoapySDRDevice_readStream(ctx->sdr, ctx->rx_stream, (void* const*)buffs, *nsamples, &flags, &timeNs, timeout_us);
size_t samples_received = 0;
if(ret <= 0) {
LOG(LVL_ERR, "readStream fail: %s", SoapySDRDevice_lastError());
return ERR_SOAPY;
while(samples_received < *nsamples) {
size_t samples_remaining = *nsamples - samples_received;
size_t block_samples = BLOCK_SIZE;
if(samples_remaining < BLOCK_SIZE) {
block_samples = samples_remaining;
}
void *buffs[] = {(void*)(rx_block)};
long long timeNs;
int flags;
int ret = SoapySDRDevice_readStream(ctx->sdr, ctx->rx_stream, (void* const*)buffs, block_samples, &flags, &timeNs, timeout_us);
if(ret <= 0) {
LOG(LVL_ERR, "readStream fail: %s", SoapySDRDevice_lastError());
return ERR_SOAPY;
} else if((size_t)ret != *nsamples) {
LOG(LVL_WARN, "readStream() did not receive all requested samples: %i/%zu", ret, block_samples);
}
float complex *block_start = samples + samples_received;
for(size_t i = 0; i < (size_t)ret; i++) {
block_start[i] = rx_block[i] - (SDR_RX_OFFSET_I + I * SDR_RX_OFFSET_Q);
}
samples_received += ret;
}
*nsamples = ret;
*nsamples = samples_received;
return OK;
}