third-party
/
HamShield
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Add calculators for frequency steps. Accumulator has a typedef now. Optimize tick.

This commit is contained in:
Stephen Olesen 2015-07-03 15:23:39 -06:00
parent 5fd0fdf154
commit acc4aebe03
2 changed files with 43 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
DDS.cpp
View File

@ -59,22 +59,27 @@ void DDS::stop() {
}
// Set our current sine wave frequency in Hz
void DDS::setFrequency(unsigned short freq) {
ddsAccumulator_t DDS::calcFrequency(unsigned short freq) {
// Fo = (M*Fc)/2^N
// M = (Fo/Fc)*2^N
ddsAccumulator_t newStep;
if(refclk == DDS_REFCLK_DEFAULT) {
// Try to use precalculated values if possible
if(freq == 2200) {
stepRate = (2200.0 / (DDS_REFCLK_DEFAULT+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);
newStep = (2200.0 / (DDS_REFCLK_DEFAULT+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);
} else if (freq == 1200) {
stepRate = (1200.0 / (DDS_REFCLK_DEFAULT+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);
newStep = (1200.0 / (DDS_REFCLK_DEFAULT+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);
} else if(freq == 2400) {
newStep = (2400.0 / (DDS_REFCLK_DEFAULT+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);
} else if (freq == 1500) {
newStep = (1500.0 / (DDS_REFCLK_DEFAULT+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);
} else if (freq == 600) {
stepRate = (600.0 / (DDS_REFCLK_DEFAULT+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);
newStep = (600.0 / (DDS_REFCLK_DEFAULT+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);
}
} else {
// BUG: Step rate isn't properly calculated here, it gets the wrong frequency
stepRate = pow(2,ACCUMULATOR_BITS)*freq / (refclk+DDS_REFCLK_OFFSET);
newStep = pow(2,ACCUMULATOR_BITS)*freq / (refclk+DDS_REFCLK_OFFSET);
}
return newStep;
}
// Degrees should be between -360 and +360 (others don't make much sense)
@ -134,19 +139,25 @@ void DDS::clockTick() {
}
uint8_t DDS::getDutyCycle() {
#if ACCUMULATOR_BIT_SHIFT >= 24
uint16_t phAng;
#else
uint8_t phAng;
#endif
#if ACCUMULATOR_BIT_SHIFT >= 24
uint16_t phAng;
#else
uint8_t phAng;
#endif
if(amplitude == 0) // Shortcut out on no amplitude
return 128>>(8-COMPARATOR_BITS);
phAng = (accumulator >> ACCUMULATOR_BIT_SHIFT);
int8_t position = pgm_read_byte_near(ddsSineTable + phAng); //>>(8-COMPARATOR_BITS);
// Apply scaling and return
int16_t scaled = position;
// output = ((duty * amplitude) / 256) + 128
// This keeps amplitudes centered around 50% duty
scaled *= amplitude;
scaled >>= 8+(8-COMPARATOR_BITS);
if(amplitude != 255) { // Amplitude is reduced, so do the full math
scaled *= amplitude;
scaled >>= 8+(8-COMPARATOR_BITS);
} else { // Otherwise, only shift for the comparator bits
scaled >>= (8-COMPARATOR_BITS);
}
scaled += 128>>(8-COMPARATOR_BITS);
return scaled;
}

31
DDS.h
View File

@ -6,7 +6,7 @@
// Use pin 3 for PWM? If not defined, use pin 11
// Quality on pin 3 is higher than on 11, as it can be clocked faster
// when the COMPARATOR_BITS value is less than 8
// #define DDS_PWM_PIN_3
#define DDS_PWM_PIN_3
// Normally, we turn on timer2 and timer1, and have ADC sampling as our clock
// Define this to only use Timer2, and not start the ADC clock
@ -18,8 +18,10 @@
#ifdef SHORT_ACCUMULATOR
#define ACCUMULATOR_BITS 16
typedef int16_t ddsAccumulator_t;
#else
#define ACCUMULATOR_BITS 32
typedef int32_t ddsAccumulator_t;
#endif
// If defined, the timer will idle at 50% duty cycle
@ -42,11 +44,16 @@
// This is how often we'll perform a phase advance, as well as ADC sampling
// rate. The higher this value, the smoother the output wave will be, at the
// expense of CPU time. It maxes out around 62000 (TBD)
// May be overridden in the sketch to improve performance
#ifndef DDS_REFCLK_DEFAULT
#define DDS_REFCLK_DEFAULT 38400
#endif
// As each Arduino crystal is a little different, this can be fine tuned to
// provide more accurate frequencies. Adjustments in the range of hundreds
// is a good start.
#ifndef DDS_REFCLK_OFFSET
#define DDS_REFCLK_OFFSET 0
#endif
#ifdef DDS_USE_ONLY_TIMER2
// TODO: Figure out where this clock value is generated from
@ -172,7 +179,7 @@ static const int8_t ddsSineTable[256] PROGMEM = {
class DDS {
public:
DDS(): refclk(DDS_REFCLK_DEFAULT), accumulator(0), running(false),
timeLimited(false), tickDuration(0), amplitude(0)
timeLimited(false), tickDuration(0), amplitude(255)
{};
// Start all of the timers needed
@ -210,9 +217,15 @@ public:
delay(duration);
}
// Use these to get some calculated values for specific frequencies
// or to get the current frequency stepping rate.
ddsAccumulator_t calcFrequency(unsigned short freq);
ddsAccumulator_t getPhaseAdvance() { return stepRate; };
// Our maximum clock isn't very high, so our highest
// frequency supported will fit in a short.
void setFrequency(unsigned short freq);
void setFrequency(unsigned short freq) { stepRate = calcFrequency(freq); };
void setPrecalcFrequency(ddsAccumulator_t freq) { stepRate = freq; };
// Handle phase shifts
void setPhaseDeg(int16_t degrees);
@ -244,15 +257,9 @@ private:
volatile unsigned long tickDuration;
volatile bool timeLimited;
volatile unsigned char amplitude;
#ifdef SHORT_ACCUMULATOR
volatile unsigned short accumulator;
volatile unsigned short stepRate;
unsigned short refclk;
#else
volatile unsigned long accumulator;
volatile unsigned long stepRate;
unsigned long refclk;
#endif
volatile ddsAccumulator_t accumulator;
volatile ddsAccumulator_t stepRate;
ddsAccumulator_t refclk;
static DDS *sDDS;
};