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[ALSA] usb-audio: fix Emagic MIDI protocol handling 

USB generic driver
Emagic devices pad their packets not with 0xff bytes but with a 0xff
byte followed by garbage, so we have to stop at the first such byte.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
This commit is contained in:
Clemens Ladisch 2005-08-25 11:10:05 +02:00 committed by Jaroslav Kysela
parent a278655ff5
commit c347e9fca7
1 changed files with 12 additions and 5 deletions
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17
sound/usb/usbmidi.c
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@ -594,17 +594,20 @@ static void snd_usbmidi_emagic_finish_out(snd_usb_midi_out_endpoint_t* ep)
static void snd_usbmidi_emagic_input(snd_usb_midi_in_endpoint_t* ep,
uint8_t* buffer, int buffer_length)
{
/* ignore padding bytes at end of buffer */
while (buffer_length > 0 && buffer[buffer_length - 1] == 0xff)
--buffer_length;
int i;
/* FF indicates end of valid data */
for (i = 0; i < buffer_length; ++i)
if (buffer[i] == 0xff) {
buffer_length = i;
break;
}
/* handle F5 at end of last buffer */
if (ep->seen_f5)
goto switch_port;
while (buffer_length > 0) {
int i;
/* determine size of data until next F5 */
for (i = 0; i < buffer_length; ++i)
if (buffer[i] == 0xf5)
@ -671,6 +674,10 @@ static void snd_usbmidi_emagic_output(snd_usb_midi_out_endpoint_t* ep)
break;
}
}
if (buf_free < ep->max_transfer && buf_free > 0) {
*buf = 0xff;
--buf_free;
}
ep->urb->transfer_buffer_length = ep->max_transfer - buf_free;
}