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uSDR-pico/dsp_fft.c

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/*
* dsp_fft.c
* ==>TO BE INCLUDED IN dsp.c
*
* Created: May 2022
* Author: Arjan te Marvelde
*
* Signal processing of RX and TX branch, to be run on the second processor core (CORE1).
* A branch has a dedicated routine that must run on set times.
* In this case it runs when half FFT_SIZE of samples is ready to be processed.
*
*
* The pace for sampling is set by a timer at 64usec (15.625 kHz)
* The associated timer callback routine:
* - handles data transfer to/from physical interfaces
* - starts a new ADC conversion sequence
* - maintains dsp_tick counter
* - when dsp_tick == FFT_SIZE/2 (one buffer), the dsp-loop is triggered.
*
* The ADC functions in round-robin and fifo mode, triggering IRQ after 3 conversions (ADC[0..2])
* The ADC FIFO IRQ handler reads the 3 samples from the fifo after stopping the ADC
*
* Buffer structure, built from half FFT_SIZE buffers.
* The I, Q and A external interfaces communicate each through 3x buffers.
* One buffer is being filled or emptied, depending on data direction.
* The other two are swapped with the FFT signal processing buffers.
* Since we use complex FFT, the algorithm uses 4x buffers.
*
* I, Q and A buffers are used as queues. RX case looks like:
*
* +--+--+--+ +--+--+--+
* i --> | | | | | | | | --> a
* +--+--+--+ +--+--+--+
* \ \ \ +--+--+ / /
* ---------> | | | -------
* +--+--+ FFT-DSP-iFFT
* ---------> | | |
* / / / +--+--+
* +--+--+--+
* q --> | | | |
* +--+--+--+
*
* RX, when triggered by timer callback:
* - The oldest two I and Q buffers are copied into the FFT buffers
* - FFT is executed
* - Signal processing is done
* - iFFT is executed
* - The oldest real FFT buffer is moved to the A output queue
*
* +--+--+--+ +--+--+--+
* a --> | | | | | | | | --> i
* +--+--+--+ +--+--+--+
* \ \ \ +--+--+ / /
* --------> | | | -------
* +--+--+ FFT-DSP-iFFT
* | | | -------
* +--+--+ \ \
* +--+--+--+
* | | | | --> q
* +--+--+--+
*
* TX, when triggered by timer callback:
* - The oldest two A buffers are copied to the real FFT buffer, the imaginary FFT buffer is nulled
* - FFT is executed
* - Signal processing is done
* - iFFT is executed
* - The oldest FFT buffers are appended to the I/Q output queues
*
* The bin step is the sampling frequency divided by the FFT_SIZE.
* So for S_RATE=15625 and FFT_SIZE=1024 this step is 15625/1024=15.259 Hz
* The Carrier offset (Fc) is at about half the Nyquist frequency: bin 256 or 3906 Hz
*
*/
#include "uSDR.h"
/*
* FFT buffer allocation
* Buffer size is FFT_SIZE/2 (see fix_fft.h).
* In case FFT_SIZE of 1024, a buffer is 1kB
* RX: 3 buffers for I samples, 3 buffers for Q samples, 3 buffers for Audio
* DSP: 4 buffers for FFT, complex samples and these have to be consecutive!
* TX: re-use RX buffers in reverse order
* Total of 13kByte RAM is required.
* Samples are 16 bit signed integer, but align buffers on 32bit boundaries
* dsp_tick points into I, Q and A buffers, so wrap once per two FFTs
* When tick==FFT_SIZE/2: do buffer copy
*/
#define BUFSIZE FFT_SIZE/2
int16_t I_buf[3][BUFSIZE] __attribute__((aligned(4))); // I sample queue, 3x buffer of FFT_SIZE/2
int16_t Q_buf[3][BUFSIZE] __attribute__((aligned(4))); // Q sample queue, 3x buffer of FFT_SIZE/2
int16_t A_buf[3][BUFSIZE] __attribute__((aligned(4))); // A sample queue, 3x buffer of FFT_SIZE/2
int16_t XI_buf[FFT_SIZE] __attribute__((aligned(4))); // Re FFT buffer, 1x buffer of FFT_SIZE
int16_t XQ_buf[FFT_SIZE] __attribute__((aligned(4))); // Im FFT buffer, 1x buffer of FFT_SIZE
// Sample buffer indexes, updated by timer callback
volatile int dsp_active = 0; // I, Q, A active buffer number (0..2)
volatile uint32_t dsp_tick = 0; // Index in active buffer
volatile uint32_t dsp_tickx = 0; // Load indicator DSP loop
// Spectrum bins for a frequency
#define BIN(f) (int)(((f)*FFT_SIZE+S_RATE/2)/S_RATE)
#define BIN_FC 256 // BIN_FC > BIN_3000 to avoid aliasing!
#define BIN_100 7
#define BIN_300 20
#define BIN_900 59
#define BIN_3000 197
/*
* This applies a bandpass filter to XI and XQ buffers
* lowbin and highbin edges must be between 3 and FFT_SIZE/2 - 3
* sign: <0 only LSB is passed
* >0 only USB is passed
* =0 LSB and USB are passed
* Edge is a 7 bin raised cosine flank, i.e. 100Hz wide
* Coefficients are: 0, 0.067, 0.25, 0.5, 0.75, 0.933, 1
* where the edge bin is in the center of this flank
* Note: maybe make slope less steep, e.g. 9 or 11 bins
*/
void __not_in_flash_func(dsp_bandpass)(int lowbin, int highbin, int sign)
{
int i, lo1, lo2, hi1, hi2;
if ((lowbin<3)||(highbin>(FFT_SIZE/2-3))||(highbin-lowbin<6)) return;
XI_buf[0] = 0; XQ_buf[0] = 0;
// Boundaries are inclusive
if (sign>=0) { lo1 = lowbin-2; lo2 = highbin+2; }
if (sign<=0) { hi1 = FFT_SIZE-highbin-2; hi2 = FFT_SIZE-lowbin+2; }
// Null all bins excluded from filter
for (i=1; i<lo1; i++) { XI_buf[i] = 0; XQ_buf[i] = 0; }
for (i=lo2+1; i<hi1; i++) { XI_buf[i] = 0; XQ_buf[i] = 0; }
for (i=hi2+1; i<FFT_SIZE; i++) { XI_buf[i] = 0; XQ_buf[i] = 0; }
// Calculate edges, raised cosine
i=lo1; // USB
XI_buf[i] = XI_buf[i]*0.067; XQ_buf[i] = XQ_buf[i]*0.067; i++;
XI_buf[i] = XI_buf[i]*0.250; XQ_buf[i] = XQ_buf[i]*0.250; i++;
XI_buf[i] = XI_buf[i]*0.500; XQ_buf[i] = XQ_buf[i]*0.500; i++;
XI_buf[i] = XI_buf[i]*0.750; XQ_buf[i] = XQ_buf[i]*0.750; i++;
XI_buf[i] = XI_buf[i]*0.933; XQ_buf[i] = XQ_buf[i]*0.933;
i=lo2;
XI_buf[i] = XI_buf[i]*0.067; XQ_buf[i] = XQ_buf[i]*0.067; i--;
XI_buf[i] = XI_buf[i]*0.250; XQ_buf[i] = XQ_buf[i]*0.250; i--;
XI_buf[i] = XI_buf[i]*0.500; XQ_buf[i] = XQ_buf[i]*0.500; i--;
XI_buf[i] = XI_buf[i]*0.750; XQ_buf[i] = XQ_buf[i]*0.750; i--;
XI_buf[i] = XI_buf[i]*0.933; XQ_buf[i] = XQ_buf[i]*0.933;
i=hi1; // LSB
XI_buf[i] = XI_buf[i]*0.067; XQ_buf[i] = XQ_buf[i]*0.067; i++;
XI_buf[i] = XI_buf[i]*0.250; XQ_buf[i] = XQ_buf[i]*0.250; i++;
XI_buf[i] = XI_buf[i]*0.500; XQ_buf[i] = XQ_buf[i]*0.500; i++;
XI_buf[i] = XI_buf[i]*0.750; XQ_buf[i] = XQ_buf[i]*0.750; i++;
XI_buf[i] = XI_buf[i]*0.933; XQ_buf[i] = XQ_buf[i]*0.933;
i=hi2;
XI_buf[i] = XI_buf[i]*0.067; XQ_buf[i] = XQ_buf[i]*0.067; i--;
XI_buf[i] = XI_buf[i]*0.250; XQ_buf[i] = XQ_buf[i]*0.250; i--;
XI_buf[i] = XI_buf[i]*0.500; XQ_buf[i] = XQ_buf[i]*0.500; i--;
XI_buf[i] = XI_buf[i]*0.750; XQ_buf[i] = XQ_buf[i]*0.750; i--;
XI_buf[i] = XI_buf[i]*0.933; XQ_buf[i] = XQ_buf[i]*0.933;
}
/** CORE1: RX branch **/
/*
* Execute RX branch signal processing
* max time to spend is <32ms (BUFSIZE*TIM_US)
* The pre-processed I/Q samples are passed in I_BUF and Q_BUF
* The calculated A samples are passed in A_BUF
*/
volatile int scale0;
volatile int scale1;
bool __not_in_flash_func(rx)(void)
{
int b;
int i;
int16_t *ip, *qp, *ap, *xip, *xqp;
int16_t peak;
b = dsp_active; // Point to Active sample buffer
/*** Copy saved I/Q buffers to FFT filter buffer ***/
if (++b > 2) b = 0; // Point to Old Saved sample buffer
ip = &I_buf[b][0]; xip = &XI_buf[0];
qp = &Q_buf[b][0]; xqp = &XQ_buf[0];
for (i=0; i<BUFSIZE; i++)
{
*xip++ = *ip++;
*xqp++ = *qp++;
}
if (++b > 2) b = 0; // Point to New Saved sample buffer
ip = &I_buf[b][0]; xip = &XI_buf[BUFSIZE];
qp = &Q_buf[b][0]; xqp = &XQ_buf[BUFSIZE];
for (i=0; i<BUFSIZE; i++)
{
*xip++ = *ip++;
*xqp++ = *qp++;
}
/*** Execute FFT ***/
scale0 = fix_fft(&XI_buf[0], &XQ_buf[0], false); // Frequency domain filter input
/*** Shift and filter sidebands ***/
// At this point USB and LSB surround Fc
// The desired sidebands must be shifted to their target positions around 0
// Pos USB to bin 0 and Neg USB to bin FFT_SIZE, or
// Neg LSB to bin 0 and Pos LSB to bin FFT_SIZE, or
// Pos USB to bin 0 and Pos LSB to bin FFT_SIZE
XI_buf[0] = 0; XQ_buf[0] = 0; // No DC
switch (dsp_mode)
{
case MODE_USB:
// Shift Fc + USB to 0Hz + USB
for (i=1; i<BIN_3000; i++)
{
XI_buf[i] = XI_buf[i+BIN_FC];
XI_buf[FFT_SIZE-i] = XI_buf[FFT_SIZE-BIN_FC-i];
XQ_buf[i] = XQ_buf[i+BIN_FC];
XQ_buf[FFT_SIZE-i] = XQ_buf[FFT_SIZE-BIN_FC-i];
}
// Bandpass DSB (2x USB)
dsp_bandpass(BIN_100, BIN_3000, 0);
break;
case MODE_LSB:
// Shift Fc - LSB to 0Hz - LSB
for (i=1; i<BIN_3000; i++)
{
XI_buf[BUFSIZE-i] = XI_buf[BIN_FC-i];
XI_buf[i] = XI_buf[FFT_SIZE-BIN_FC+i];
XI_buf[FFT_SIZE-i] = XI_buf[BUFSIZE-i];
XQ_buf[BUFSIZE-i] = XQ_buf[BIN_FC-i];
XQ_buf[i] = XQ_buf[FFT_SIZE-BIN_FC+i];
XQ_buf[FFT_SIZE-i] = XQ_buf[BUFSIZE-i];
}
// Bandpass DSB (2x LSB)
dsp_bandpass(BIN_100, BIN_3000, 0);
break;
case MODE_AM:
// Shift the rest to the right place
for (i=1; i<BIN_3000; i++)
{
XI_buf[FFT_SIZE-i] = XI_buf[BIN_FC-i];
XI_buf[i] = XI_buf[BIN_FC+i];
XQ_buf[FFT_SIZE-i] = XQ_buf[BIN_FC-i];
XQ_buf[i] = XQ_buf[BIN_FC+i];
}
// Bandpass DSB (LSB + USB)
dsp_bandpass(BIN_100, BIN_3000, 0);
break;
case MODE_CW:
// Shift carrier from Fc to 900Hz
for (i=-BIN_900+1; i<BIN_900-1; i++)
{
XI_buf[i+BIN_900] = XI_buf[BIN_FC+i];
XI_buf[FFT_SIZE-i-BIN_900] = XI_buf[FFT_SIZE-BIN_FC-i];
XQ_buf[i+BIN_900] = XQ_buf[BIN_FC+i];
XQ_buf[FFT_SIZE-i-BIN_900] = XQ_buf[FFT_SIZE-BIN_FC-i];
}
// Bandpass CW, 600Hz
dsp_bandpass(BIN_900-BIN_300, BIN_900+BIN_300, 0);
break;
}
/*** Execute inverse FFT ***/
scale1 = fix_fft(&XI_buf[0], &XQ_buf[0], true);
/*** Export FFT buffer to A ***/
b = dsp_active; // Assume active buffer not changed, i.e. no overruns
if (++b > 2) b = 0; // Point to oldest (will be next for output)
ap = &A_buf[b][0]; xip = &XI_buf[BUFSIZE];
for (i=0; i<BUFSIZE; i++)
{
*ap++ = *xip++; // Copy newest results
}
/*** Scale down into DAC_RANGE! ***/
peak = 256;
for (i=0; i<BUFSIZE; i++)
{
A_buf[b][i] /= peak;
}
return true;
}
/** CORE1: TX branch **/
/*
* Execute TX branch signal processing
* max time to spend is <32ms (BUFSIZE*TIM_US)
* The pre-processed A samples are passed in A_BUF
* The calculated I and Q samples are passed in I_BUF and Q_BUF
*/
bool __not_in_flash_func(tx)(void)
{
int b;
int i;
int16_t *ip, *qp, *ap, *xip, *xqp;
int16_t peak;
b = dsp_active; // Point to Active sample buffer
/*** Copy saved A buffers to FFT buffers, NULL Im. part ***/
if (++b > 2) b = 0; // Point to Old Saved sample buffer
ap = &A_buf[b][0]; xip = &XI_buf[0];
xqp = &XQ_buf[0];
for (i=0; i<BUFSIZE; i++)
{
*xip++ = *ip++;
*xqp++ = 0;
}
if (++b > 2) b = 0; // Point to New Saved sample buffer
ap = &A_buf[b][0]; xip = &XI_buf[BUFSIZE];
xqp = &XQ_buf[BUFSIZE];
for (i=0; i<BUFSIZE; i++)
{
*xip++ = *ip++;
*xqp++ = 0;
}
/*** Execute FFT ***/
scale0 = fix_fft(&XI_buf[0], &XQ_buf[0], false);
/*** Shift and filter sidebands ***/
XI_buf[0] = 0; XQ_buf[0] = 0; // No DC
switch (dsp_mode)
{
case MODE_USB:
// Bandpass Audio, USB only
dsp_bandpass(BIN_100, BIN_3000, 1);
// Shift USB up to to Fc, assumes Fc > bandwidth
for (i=1; i<BIN_3000; i++)
{
XI_buf[BIN_FC+i] = XI_buf[i];
XQ_buf[BIN_FC+i] = XQ_buf[i];
XI_buf[i] = 0;
XQ_buf[i] = 0;
}
for (i=1; i<BIN_3000; i++)
{
XI_buf[FFT_SIZE-BIN_FC-i] = XI_buf[BIN_FC+i];
XQ_buf[FFT_SIZE-BIN_FC-i] = XQ_buf[BIN_FC+i];
}
break;
case MODE_LSB:
// Bandpass Audio, LSB only
dsp_bandpass(BIN_100, BIN_3000, -1);
// Shift LSB up to Fc
for (i=1; i<BIN_3000; i++)
{
XI_buf[BIN_FC-i] = XI_buf[FFT_SIZE-i];
XQ_buf[BIN_FC-i] = XQ_buf[FFT_SIZE-i];
XI_buf[FFT_SIZE-i] = 0;
XQ_buf[FFT_SIZE-i] = 0;
}
for (i=1; i<BIN_3000; i++)
{
XI_buf[FFT_SIZE-BIN_FC+i] = XI_buf[BIN_FC-i];
XQ_buf[FFT_SIZE-BIN_FC+i] = XQ_buf[BIN_FC-i];
}
break;
case MODE_AM:
// Bandpass Audio
dsp_bandpass(BIN_100, BIN_3000, 0);
// Shift DSB up to Fc
for (i=1; i<BIN_3000; i++)
{
XI_buf[BIN_FC+i] = XI_buf[i];
XQ_buf[BIN_FC+i] = XQ_buf[i];
XI_buf[i] = 0;
XQ_buf[i] = 0;
XI_buf[BIN_FC-i] = XI_buf[FFT_SIZE-i];
XQ_buf[BIN_FC-i] = XQ_buf[FFT_SIZE-i];
XI_buf[FFT_SIZE-i] = 0;
XQ_buf[FFT_SIZE-i] = 0;
}
for (i=1; i<BIN_3000; i++)
{
XI_buf[FFT_SIZE-BIN_FC-i] = XI_buf[BIN_FC+i];
XQ_buf[FFT_SIZE-BIN_FC-i] = XQ_buf[BIN_FC+i];
XI_buf[FFT_SIZE-BIN_FC+i] = XI_buf[BIN_FC-i];
XQ_buf[FFT_SIZE-BIN_FC+i] = XQ_buf[BIN_FC-i];
}
break;
case MODE_CW:
// Create a carrier on 900Hz from Fc
break;
}
/*** Execute inverse FFT ***/
scale1 = fix_fft(&XI_buf[0], &XQ_buf[0], true);
/*** Export FFT buffer to I and Q ***/
b = dsp_active; // Assume active buffer not changed, i.e. no overruns
if (++b > 2) b = 0; // Point to oldest (will be next for output)
qp = &Q_buf[b][0]; xqp = &XQ_buf[BUFSIZE];
ip = &I_buf[b][0]; xip = &XI_buf[BUFSIZE];
for (i=0; i<BUFSIZE; i++)
{
*qp++ = *xqp++; // Copy newest results
*ip++ = *xip++; // Copy newest results
}
/*** Scale down into DAC_RANGE! ***/
peak = 256;
for (i=0; i<BUFSIZE; i++)
{
Q_buf[b][i] /= peak;
I_buf[b][i] /= peak;
}
return true;
}
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