@@ -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;
}
@@ -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;
Do no send MIDI bytes at the full rate at which FireWire packets happen to be sent, but restrict them to the actual rate of a real MIDI port. This is required by the specification, and prevents data loss when the device's buffer overruns. Signed-off-by: Clemens Ladisch <clemens@ladisch.de> --- sound/firewire/amdtp.c | 61 +++++++++++++++++++++++++++++++++++++++++++----- sound/firewire/amdtp.h | 2 ++ 2 files changed, 57 insertions(+), 6 deletions(-)