picodvi: pass the sample rate to hstx_packet_set_audio_samples

It takes the rate in Hz, like hstx_packet_set_audio_infoframe, and
looks up the IEC 60958 sample frequency code itself, as upstream
pico_hdmi does. The packets sent are unchanged.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: mikeysklar

ports/raspberrypi/common-hal/picodvi/AudioOut.c

@@ -28,15 +28,13 @@ typedef struct {
     uint32_t sample_rate;
     // The usual ACR N, for when no N gives an exact CTS.
     uint32_t usual_n;
-    // IEC 60958 channel status byte 3.
-    uint8_t channel_status;
 } dvi_audio_rate_t;
 
 // The basic audio rates every DVI sink takes.
 static const dvi_audio_rate_t dvi_audio_rates[] = {
-    { 32000, 4096, 0x03 },
-    { 44100, 6272, 0x00 },
-    { 48000, 6144, 0x02 },
+    { 32000, 4096 },
+    { 44100, 6272 },
+    { 48000, 6144 },
 };
 #define DVI_AUDIO_RATE_COUNT MP_ARRAY_SIZE(dvi_audio_rates)
 #define DVI_AUDIO_H_TOTAL (MODE_640_H_FRONT_PORCH + MODE_640_H_SYNC_WIDTH + MODE_640_H_BACK_PORCH + MODE_640_H_ACTIVE_PIXELS)
@@ -286,7 +284,7 @@ static void dvi_audio_init_packets(dvi_audio_state_t *audio) {
     // Frame position 4 never sets the block start flag, and frames 4 to 7
     // carry no channel status bits, so silence is the same at every rate.
     audio_sample_t silence[4] = {{0}};
-    hstx_packet_set_audio_samples(&packet, silence, 4, 4, dvi_audio_rates[DVI_AUDIO_RATE_COUNT - 1].channel_status);
+    hstx_packet_set_audio_samples(&packet, silence, 4, 4, dvi_audio_rates[DVI_AUDIO_RATE_COUNT - 1].sample_rate);
     for (int vsync = 0; vsync < 2; vsync++) {
         dvi_audio_encode(audio->silence[vsync], &packet, vsync);
     }
@@ -468,7 +466,7 @@ static const uint32_t *dvi_audio_next_packet(dvi_audio_state_t *audio, const int
             }
             hstx_packet_t packet;
             audio->channel_frame = hstx_packet_set_audio_samples(&packet, packet_samples, n, audio->channel_frame,
-                dvi_audio_rates[audio->rate_index].channel_status);
+                dvi_audio_rates[audio->rate_index].sample_rate);
             uint32_t *buffer = audio->pool[audio->pool_head];
             dvi_audio_encode(buffer, &packet, vsync);
             audio->pool_position[audio->pool_head] = audio->write_position;

ports/raspberrypi/common-hal/picodvi/dvi_audio_packet.c

@@ -183,8 +183,22 @@ void hstx_packet_set_avi_infoframe(hstx_packet_t *packet, uint8_t vic, uint8_t p
     compute_all_parity(packet);
 }
 
+// IEC 60958-3 channel status byte 3 sample frequency code.
+static uint8_t channel_status_sample_frequency(uint32_t sample_rate) {
+    switch (sample_rate) {
+        case 32000:
+            return 0x03;
+        case 44100:
+            return 0x00;
+        case 48000:
+            return 0x02;
+        default:
+            return 0x01; // Sample rate not indicated.
+    }
+}
+
 int hstx_packet_set_audio_samples(hstx_packet_t *packet, const audio_sample_t *samples, int num_samples,
-    int frame_count, uint8_t channel_status) {
+    int frame_count, uint32_t sample_rate) {
     hstx_packet_init(packet);
     if (num_samples < 1) {
         num_samples = 1;
@@ -209,6 +223,7 @@ int hstx_packet_set_audio_samples(hstx_packet_t *packet, const audio_sample_t *s
     packet->header[2] = b_flags << 4;
     compute_header_parity(packet);
 
+    uint8_t sample_frequency = channel_status_sample_frequency(sample_rate);
     for (int i = 0; i < num_samples; i++) {
         uint8_t *d = packet->subpacket[i];
         int16_t left = samples[i].left;
@@ -221,10 +236,9 @@ int hstx_packet_set_audio_samples(hstx_packet_t *packet, const audio_sample_t *s
         d[4] = right & 0xFF;
         d[5] = (right >> 8) & 0xFF;
 
-        // IEC 60958 byte 0 = 0x04 (copy permitted), byte 3 = channel_status
-        // (the sample rate).
+        // IEC 60958 byte 0 = 0x04 (copy permitted), byte 3 = sample frequency.
         int frame = (frame_count + i) % 192;
-        uint8_t status = frame / 8 == 0 ? 0x04 : (frame / 8 == 3 ? channel_status : 0);
+        uint8_t status = frame / 8 == 0 ? 0x04 : (frame / 8 == 3 ? sample_frequency : 0);
         uint8_t c = (status >> (frame % 8)) & 1;
         bool p_left = compute_parity3(d[1], d[2], c);
         bool p_right = compute_parity3(d[4], d[5], c);

ports/raspberrypi/common-hal/picodvi/dvi_audio_packet.h

@@ -35,5 +35,5 @@ void hstx_packet_set_acr(hstx_packet_t *packet, uint32_t n, uint32_t cts);
 void hstx_packet_set_audio_infoframe(hstx_packet_t *packet, uint32_t sample_rate, uint8_t channels, uint8_t bits_per_sample);
 void hstx_packet_set_avi_infoframe(hstx_packet_t *packet, uint8_t vic, uint8_t pixel_repetition);
 int hstx_packet_set_audio_samples(hstx_packet_t *packet, const audio_sample_t *samples, int num_samples, int frame_count,
-    uint8_t channel_status);
+    uint32_t sample_rate);
 void hstx_encode_data_island(hstx_data_island_t *out, const hstx_packet_t *packet, bool vsync_active, bool hsync_active);