1 files changed, 33 insertions, 7 deletions

diff --git a/src/drivers/pcm_buffer.cpp b/src/drivers/pcm_buffer.cpp
index 071f5cea..bc58d4b9 100644
--- a/src/drivers/pcm_buffer.cpp
+++ b/src/drivers/pcm_buffer.cpp
@@ -25,7 +25,8 @@ namespace drivers {
 
 [[maybe_unused]] static const char kTag[] = "pcmbuf";
 
-PcmBuffer::PcmBuffer(size_t size_in_samples) : sent_(0), received_(0) {
+PcmBuffer::PcmBuffer(size_t size_in_samples)
+    : sent_(0), received_(0), suspended_(false) {
   size_t size_in_bytes = size_in_samples * sizeof(int16_t);
   ESP_LOGI(kTag, "allocating pcm buffer of size %u (%uKiB)", size_in_samples,
            size_in_bytes / 1024);
@@ -49,18 +50,26 @@ auto PcmBuffer::send(std::span<const int16_t> data) -> size_t {
   return data.size();
 }
 
-IRAM_ATTR auto PcmBuffer::receive(std::span<int16_t> dest, bool isr)
+IRAM_ATTR auto PcmBuffer::receive(std::span<int16_t> dest, bool mix, bool isr)
     -> BaseType_t {
+  if (suspended_) {
+    if (!mix) {
+      std::fill_n(dest.begin(), dest.size(), 0);
+    }
+    return false;
+  }
+
   size_t first_read = 0, second_read = 0;
   BaseType_t ret1 = false, ret2 = false;
-  std::tie(first_read, ret1) = readSingle(dest, isr);
+  std::tie(first_read, ret1) = readSingle(dest, mix, isr);
 
   if (first_read < dest.size()) {
-    std::tie(second_read, ret2) = readSingle(dest.subspan(first_read), isr);
+    std::tie(second_read, ret2) =
+        readSingle(dest.subspan(first_read), mix, isr);
   }
 
   size_t total_read = first_read + second_read;
-  if (total_read < dest.size()) {
+  if (total_read < dest.size() && !mix) {
     std::fill_n(dest.begin() + total_read, dest.size() - total_read, 0);
   }
 
@@ -85,6 +94,10 @@ auto PcmBuffer::isEmpty() -> bool {
          xRingbufferGetCurFreeSize(ringbuf_);
 }
 
+auto PcmBuffer::suspend(bool s) -> void {
+  suspended_ = s;
+}
+
 auto PcmBuffer::totalSent() -> uint32_t {
   return sent_;
 }
@@ -93,7 +106,9 @@ auto PcmBuffer::totalReceived() -> uint32_t {
   return received_;
 }
 
-IRAM_ATTR auto PcmBuffer::readSingle(std::span<int16_t> dest, bool isr)
+IRAM_ATTR auto PcmBuffer::readSingle(std::span<int16_t> dest,
+                                     bool mix,
+                                     bool isr)
     -> std::pair<size_t, BaseType_t> {
   BaseType_t ret;
   size_t read_bytes = 0;
@@ -111,7 +126,18 @@ IRAM_ATTR auto PcmBuffer::readSingle(std::span<int16_t> dest, bool isr)
     return {read_samples, ret};
   }
 
-  std::memcpy(dest.data(), data, read_bytes);
+  if (mix) {
+    for (size_t i = 0; i < read_samples; i++) {
+      // Sum the two samples in a 32 bit field so that the addition is always
+      // safe.
+      int32_t sum = static_cast<int32_t>(dest[i]) +
+                    static_cast<int32_t>(reinterpret_cast<int16_t*>(data)[i]);
+      // Clip back into the range of a single sample.
+      dest[i] = std::clamp<int32_t>(sum, INT16_MIN, INT16_MAX);
+    }
+  } else {
+    std::memcpy(dest.data(), data, read_bytes);
+  }
 
   if (isr) {
     vRingbufferReturnItem(ringbuf_, data);