Hi Takashi,
Many thanks for doing this!
On 03/15/2015 05:01 PM, Takashi Sakamoto wrote:
+void snd_dg00x_protocol_write_s32(struct amdtp_stream *s,
struct snd_pcm_substream *pcm,__be32 *buffer, unsigned int frames)+{
- struct snd_pcm_runtime *runtime = pcm->runtime;
- unsigned int channels, remaining_frames, i, c;
- const u32 *src;
- static struct dot_state state;
There's no need to declare this as static. The state is per frame.
- channels = s->pcm_channels;
- src = (void *)runtime->dma_area +
frames_to_bytes(runtime, s->pcm_buffer_pointer);- remaining_frames = runtime->buffer_size - s->pcm_buffer_pointer;
- for (i = 0; i < frames; ++i) {
..it is zeroed here, anyway:
dot_state_reset(&state);
for (c = 0; c < channels; ++c) {buffer[s->pcm_positions[c]] =cpu_to_be32((*src >> 8) | 0x40000000);dot_encode_step(&state, &buffer[s->pcm_positions[c]]);src++;}buffer += s->data_block_quadlets;if (--remaining_frames == 0)src = (void *)runtime->dma_area;- }
+}
In any case, the algorithm to xor-encode the digidesign data is not yet 100% correct there. One will need to continue iterating after the last channel (feeding zero) until the state->carry (dot_scrt()) is 0x00.
The current code here only works only correctly for data on the first 4 chanels (18 [total channels] - 14 [max xor-chain length]).
I'll let Damien elaborate. He has access to a Digidesign interface and did the protocol-dumps. I only did the clean room reverse-engineering and maths on the other end.
Cheers! robin