I am currently testing my driver but I've got some problems with the "pcm machine"...as it is my first ALSA driver I am open for every hint. The code currently is not conform to linux kernel coding style, I will do all such cosmetically stuff after functionality is given.

1. Playing a file works fine, but when the ALSA middle layer triggers stop command, the DSP still has data to play, so sending a stop signal to the DSP at this moment would result in breaking the playback. The strange thing here is, that it seems there are 6 frames missing, but the buffer of the DSP is only about 3 frames long. I am not sure if the problem here is, that I am not correctly "calculating" the pcm_pointer:

static snd_pcm_uframes_t snd_card_mychip_pcm_pointer(struct snd_pcm_substream *substream) { struct snd_pcm_runtime *runtime = substream->runtime; struct snd_mychip_pcm *dpcm = runtime->private_data;

/* get the current hardware pointer */ // TODO: calc correct return value

print_log(DEBUGC "pcm pointer: ret b=%lu\n", bytes_to_frames(runtime, dpcm->pcm_buf_pos));

return bytes_to_frames(runtime, dpcm->pcm_buf_pos); }

2. when playing and capturing data simultaneously, I get troubles in both. Playback or Capture alone is working, but if both come togheter, troubles occur. The data-transfer from ALSA to DSP and DSP to ALSA I am doing in the timer function, I am not sure if this could be the problem...but to send data to the DSP I have to check a flag if the DSP is able to receive data, if so, I can send data, otherwise I have to wait until DSP is ready to receive data. That is done with dsp_sendstream. When capturing, the DSP is sending an interrupt every captured period that is available, so I store that in a buffer from where it got read frequently via the timer function (done by readbuf)...everytime when going through this function I think that this way may work, as it does normally, but I am absolutely not sure if this is a "right" way. I know that there are so called "copy" and "silence" callbacks, but using the copy callback for playback I lost frames, so I did it like it is now...

static void snd_card_mychip_pcm_timer_function(unsigned long data) { struct snd_mychip_pcm *dpcm = (struct snd_mychip_pcm *)data; unsigned long flags; int count, pos, status;

// disable interrupts spin_lock_irqsave(&dpcm->lock, flags);

// restart the timer to be called again after one jiffie = 1 ms dpcm->timer.expires = 1 + jiffies; add_timer(&dpcm->timer);

if (dpcm->substream->stream == 0) { // playback stream // increase counters by bytes per jiffie if (dpcm->sendingnotpossible == 0) { dpcm->pcm_irq_pos += dpcm->pcm_jiffie; //0..MAX_PERIOD_SIZE step=jiffie dpcm->pcm_buf_pos += dpcm->pcm_jiffie; //0..MAX_BUFFER_SIZE step=jiffie } // if pcm_count has been reached, call snd_pcm_period_elapsed // to signal the end of one period (e.g. 288 for mpg or 768 for wav) if (dpcm->pcm_irq_pos >= dpcm->pcm_count) { // >= MAX_PERIOD_SIZE? count=dpcm->pcm_count; // number of bytes to be sent pos=dpcm->pcm_buf_pos-count; // start offset in DMA buffer // try to send data to dsp status = dsp_sendstream(dpcm->substream->pcm->device, dpcm->substream->runtime->dma_area+pos, count); if (status != 0) { // sending not possible dpcm->sendingnotpossible=1; } else { // sending successful dpcm->sendingnotpossible=0; dpcm->sentframes++; if (dpcm->sentframes == 3) // 3 frames in buffer so we can start playback { // start decoder playback status=dsp_decod_action(dpcm->substream->pcm->device, DECOD_START); print_log(DEBUGA "reply of dsp_decod_action = %i\n",status); } // wrap counter if end of buffer is reached dpcm->pcm_buf_pos %= dpcm->pcm_size; // wrap this counter too dpcm->pcm_irq_pos %= dpcm->pcm_count; // tell the PCM middle layer when the buffer position goes across the prescribed period size snd_pcm_period_elapsed(dpcm->substream); print_log(DEBUGC "timer_function: Period elapsed (p) - pcm_count=%i - pcm_size=%i - src=%p - jiffie=%i\n",dpcm->pcm_count,dpcm->pcm_size,dpcm->substream->runtime->dma_area,dpcm->pcm_jiffie); } // enable interrupts spin_unlock_irqrestore(&dpcm->lock, flags); } else { // wrap counter if end of buffer is reached dpcm->pcm_buf_pos %= dpcm->pcm_size; // enable interrupts spin_unlock_irqrestore(&dpcm->lock, flags); } } else if (dpcm->substream->stream == 1) { // capture stream count = dpcm->pcm_count; // number of bytes to be captured pos = dpcm->pcm_buf_pos; // start offset in DMA buffer // read from HIF buffer status = readbuf(dpcm->substream->pcm->device, dpcm->substream->runtime->dma_area+pos, count); if (status == 0) { // we got new data from HIF buffer => increase pointers.. dpcm->pcm_buf_pos += count; // wrap counter if end of buffer is reached dpcm->pcm_buf_pos %= dpcm->pcm_size; // wrap this counter too //dpcm->pcm_irq_pos %= dpcm->pcm_count; // tell the PCM middle layer when the buffer position goes across the prescribed period size snd_pcm_period_elapsed(dpcm->substream); print_log(DEBUG "timer_function: Period elapsed (c) - pcm_count=%i - pcm_size=%i - src=%p - jiffie=%i\n",dpcm->pcm_count,dpcm->pcm_size,dpcm->substream->runtime->dma_area,dpcm->pcm_jiffie); } // enable interrupts spin_unlock_irqrestore(&dpcm->lock, flags); } }

3. Sometimes I am getting underruns with aplay or xruns with arecord. Currently I am not quite sure why they occur, but I guess this has to do with some of above problems?

-bash-3.2# aplay 20575_24k_100.wav Playing WAVE '20575_24k_100.wav ' : Signed 16 bit Little Endian, Rate 24000 Hz, Mono underrun!!! (at least 8.019 ms long)

As a reference I used the dummy driver and the tutorial Writing an ALSA Driver. If there are some other drivers that may be similar and I can look at, I am thankful for every hint! So far thanks for helping me!

Greetings, Max