diff options
| -rw-r--r-- | sound/firewire/amdtp.c | 61 | ||||
| -rw-r--r-- | sound/firewire/amdtp.h | 2 |
2 files changed, 57 insertions, 6 deletions
diff --git a/sound/firewire/amdtp.c b/sound/firewire/amdtp.c index ef399cadb8a5..0d580186ef1a 100644 --- a/sound/firewire/amdtp.c +++ b/sound/firewire/amdtp.c @@ -22,6 +22,12 @@ #define TICKS_PER_SECOND (TICKS_PER_CYCLE * CYCLES_PER_SECOND) /* + * Nominally 3125 bytes/second, but the MIDI port's clock might be + * 1% too slow, and the bus clock 100 ppm too fast. + */ +#define MIDI_BYTES_PER_SECOND 3093 + +/* * Several devices look only at the first eight data blocks. * In any case, this is more than enough for the MIDI data rate. */ @@ -226,6 +232,14 @@ sfc_found: for (i = 0; i < pcm_channels; i++) s->pcm_positions[i] = i; s->midi_position = s->pcm_channels; + + /* + * We do not know the actual MIDI FIFO size of most devices. Just + * assume two bytes, i.e., one byte can be received over the bus while + * the previous one is transmitted over MIDI. + * (The value here is adjusted for midi_ratelimit_per_packet().) + */ + s->midi_fifo_limit = rate - MIDI_BYTES_PER_SECOND * s->syt_interval + 1; } EXPORT_SYMBOL(amdtp_stream_set_parameters); @@ -467,6 +481,36 @@ static void amdtp_fill_pcm_silence(struct amdtp_stream *s, } } +/* + * To avoid sending MIDI bytes at too high a rate, assume that the receiving + * device has a FIFO, and track how much it is filled. This values increases + * by one whenever we send one byte in a packet, but the FIFO empties at + * a constant rate independent of our packet rate. One packet has syt_interval + * samples, so the number of bytes that empty out of the FIFO, per packet(!), + * is MIDI_BYTES_PER_SECOND * syt_interval / sample_rate. To avoid storing + * fractional values, the values in midi_fifo_used[] are measured in bytes + * multiplied by the sample rate. + */ +static bool midi_ratelimit_per_packet(struct amdtp_stream *s, unsigned int port) +{ + int used; + + used = s->midi_fifo_used[port]; + if (used == 0) /* common shortcut */ + return true; + + used -= MIDI_BYTES_PER_SECOND * s->syt_interval; + used = max(used, 0); + s->midi_fifo_used[port] = used; + + return used < s->midi_fifo_limit; +} + +static void midi_rate_use_one_byte(struct amdtp_stream *s, unsigned int port) +{ + s->midi_fifo_used[port] += amdtp_rate_table[s->sfc]; +} + static void amdtp_fill_midi(struct amdtp_stream *s, __be32 *buffer, unsigned int frames) { @@ -474,16 +518,21 @@ static void amdtp_fill_midi(struct amdtp_stream *s, u8 *b; for (f = 0; f < frames; f++) { - buffer[s->midi_position] = 0; b = (u8 *)&buffer[s->midi_position]; port = (s->data_block_counter + f) % 8; - if ((f >= MAX_MIDI_RX_BLOCKS) || - (s->midi[port] == NULL) || - (snd_rawmidi_transmit(s->midi[port], b + 1, 1) <= 0)) - b[0] = 0x80; - else + if (f < MAX_MIDI_RX_BLOCKS && + midi_ratelimit_per_packet(s, port) && + s->midi[port] != NULL && + snd_rawmidi_transmit(s->midi[port], &b[1], 1) == 1) { + midi_rate_use_one_byte(s, port); b[0] = 0x81; + } else { + b[0] = 0x80; + b[1] = 0; + } + b[2] = 0; + b[3] = 0; buffer += s->data_block_quadlets; } diff --git a/sound/firewire/amdtp.h b/sound/firewire/amdtp.h index cd4c4dfb3951..8a03a91e728b 100644 --- a/sound/firewire/amdtp.h +++ b/sound/firewire/amdtp.h @@ -148,6 +148,8 @@ struct amdtp_stream { bool double_pcm_frames; struct snd_rawmidi_substream *midi[AMDTP_MAX_CHANNELS_FOR_MIDI * 8]; + int midi_fifo_limit; + int midi_fifo_used[AMDTP_MAX_CHANNELS_FOR_MIDI * 8]; /* quirk: fixed interval of dbc between previos/current packets. */ unsigned int tx_dbc_interval; |