AdvancedDAC: Add support for loop mode.

Loop mode starts the DAC automatically when all buffers in the queue are
written. Once started, the DAC will continuously cycle through all of the
buffers in the queue.

Signed-off-by: iabdalkader <[email protected]>

Author: iabdalkader

src/AdvancedDAC.cpp

@@ -32,16 +32,17 @@ struct dac_descr_t {
     uint32_t dmaudr_flag;
     DMAPool<Sample> *pool;
     DMABuffer<Sample> *dmabuf[2];
+    bool loop_mode;
 };
 
 // NOTE: Both DAC channel descriptors share the same DAC handle.
 static DAC_HandleTypeDef dac = {0};
 
 static dac_descr_t dac_descr_all[] = {
     {&dac, DAC_CHANNEL_1, {DMA1_Stream4, {DMA_REQUEST_DAC1_CH1}}, DMA1_Stream4_IRQn, {TIM4},
-        DAC_TRIGGER_T4_TRGO, DAC_ALIGN_12B_R, DAC_FLAG_DMAUDR1, nullptr, {nullptr, nullptr}},
+        DAC_TRIGGER_T4_TRGO, DAC_ALIGN_12B_R, DAC_FLAG_DMAUDR1, nullptr, {nullptr, nullptr}, false},
     {&dac, DAC_CHANNEL_2, {DMA1_Stream5, {DMA_REQUEST_DAC1_CH2}}, DMA1_Stream5_IRQn, {TIM5},
-        DAC_TRIGGER_T5_TRGO, DAC_ALIGN_12B_R, DAC_FLAG_DMAUDR2, nullptr, {nullptr, nullptr}},
+        DAC_TRIGGER_T5_TRGO, DAC_ALIGN_12B_R, DAC_FLAG_DMAUDR2, nullptr, {nullptr, nullptr}, false},
 };
 
 static uint32_t DAC_RES_LUT[] = {
@@ -110,7 +111,7 @@ bool AdvancedDAC::available() {
 
 DMABuffer<Sample> &AdvancedDAC::dequeue() {
     static DMABuffer<Sample> NULLBUF;
-    if (descr != nullptr) {
+    if (descr != nullptr && !descr->loop_mode) {
         while (!available()) {
             __WFI();
         }
@@ -130,7 +131,9 @@ void AdvancedDAC::write(DMABuffer<Sample> &dmabuf) {
     dmabuf.flush();
     dmabuf.release();
 
-    if (descr->dmabuf[0] == nullptr && (++buf_count % 3) == 0) {
+    if (!descr->dmabuf[0] &&
+       ((descr->loop_mode && !descr->pool->writable()) ||
+       (!descr->loop_mode && (++buf_count % 3 == 0)))) {
         descr->dmabuf[0] = descr->pool->alloc(DMA_BUFFER_READ);
         descr->dmabuf[1] = descr->pool->alloc(DMA_BUFFER_READ);
 
@@ -148,7 +151,7 @@ void AdvancedDAC::write(DMABuffer<Sample> &dmabuf) {
     }
 }
 
-int AdvancedDAC::begin(uint32_t resolution, uint32_t frequency, size_t n_samples, size_t n_buffers) {
+int AdvancedDAC::begin(uint32_t resolution, uint32_t frequency, size_t n_samples, size_t n_buffers, bool loop) {
     // Sanity checks.
     if (resolution >= AN_ARRAY_SIZE(DAC_RES_LUT) || descr != nullptr) {
         return 0;
@@ -172,6 +175,8 @@ int AdvancedDAC::begin(uint32_t resolution, uint32_t frequency, size_t n_samples
         descr = nullptr;
         return 0;
     }
+
+    descr->loop_mode = loop;
     descr->resolution = DAC_RES_LUT[resolution];
 
     // Init and config DMA.
@@ -192,26 +197,23 @@ int AdvancedDAC::begin(uint32_t resolution, uint32_t frequency, size_t n_samples
     return 1;
 }
 
-int AdvancedDAC::stop()
-{
+int AdvancedDAC::stop() {
     if (descr != nullptr) {
         dac_descr_deinit(descr, true);
         descr = nullptr;
     }
     return 1;
 }
 
-int AdvancedDAC::frequency(uint32_t const frequency)
-{
+int AdvancedDAC::frequency(uint32_t const frequency) {
     if (descr != nullptr) {
         // Reconfigure the trigger timer.
         dac_descr_deinit(descr, false);
         hal_tim_config(&descr->tim, frequency);
     }
 }
 
-AdvancedDAC::~AdvancedDAC()
-{
+AdvancedDAC::~AdvancedDAC() {
     dac_descr_deinit(descr, true);
 }
 
@@ -227,6 +229,10 @@ void DAC_DMAConvCplt(DMA_HandleTypeDef *dma, uint32_t channel) {
         size_t ct = ! hal_dma_get_ct(dma);
         descr->dmabuf[ct]->release();
         descr->dmabuf[ct] = descr->pool->alloc(DMA_BUFFER_READ);
+        if (descr->loop_mode) {
+            // Move a buffer from the write queue to the read queue.
+            descr->pool->alloc(DMA_BUFFER_WRITE)->release();
+        }
         hal_dma_update_memory(dma, descr->dmabuf[ct]->data());
     } else {
         dac_descr_deinit(descr, false);

src/AdvancedDAC.h

@@ -45,7 +45,7 @@ class AdvancedDAC {
         bool available();
         SampleBuffer dequeue();
         void write(SampleBuffer dmabuf);
-        int begin(uint32_t resolution, uint32_t frequency, size_t n_samples=0, size_t n_buffers=0);
+        int begin(uint32_t resolution, uint32_t frequency, size_t n_samples=0, size_t n_buffers=0, bool loop=false);
         int stop();
         int frequency(uint32_t const frequency);
 };