Hi, I discovered a bug in the emu10k1 driver which I'll explain here:
I was developing an application which uses the timestamps given in the
status of the device to send S/PDIF data to it. This app worked pretty
well except that sometimes I heard sound discontinuities and then a
constant time delay between the sound and the video.
I finally found where was the problem, my results is based on the
emu10k1-debug.patch file attached. The "frame" argument is equal to 0
when the app gets the status of the device. With this patch applied I
saw some output on the console exactly at the same time the bug occured.
Adding a "else" after the "if" to prevent sw_ready from being updated
fixed the problem and the output looked like
----------------
plop 0 -1536 A B
plop 0 1536 B A
----------------
where B == A - 1536 (1536 is the period_size). These two lines were
repeated a few times during playback.
So the bug looks like a signedness problem since sw_ready is unsigned
and there is a while(sw_ready > 0), which explain the constant delay,
next in the "snd_emu10k1_fx8010_playback_transfer" function.
So the emu10k1.patch file attached fixes the problem and seems not to
introduce new ones.
Note: patches were made with the 0.9.0rc7 version of the alsa-driver
package.
Regards,
--
Arnaud.
--- alsa-kernel/pci/emu10k1/emufx.c.orig 2003-02-08 23:02:50.000000000 +0100
+++ alsa-kernel/pci/emu10k1/emufx.c 2003-02-08 23:17:09.000000000 +0100
@@ -531,6 +531,11 @@
if (diff) {
if (diff < -(snd_pcm_sframes_t) (runtime->boundary / 2))
diff += runtime->boundary;
+ if(frames == 0)
+ {
+ printk("plop %d %ld (%lu %u)\n",
+ pcm->sw_ready, diff, appl_ptr, pcm->appl_ptr);
+ }
pcm->sw_ready += diff;
}
pcm->sw_ready += frames;
--- alsa-kernel/include/emu10k1.h.orig 2003-02-08 23:00:43.000000000 +0100
+++ alsa-kernel/include/emu10k1.h 2003-02-08 23:02:02.000000000 +0100
@@ -879,7 +879,8 @@
unsigned char etram[32]; /* external TRAM address & data */
unsigned int sw_data, hw_data;
unsigned int sw_io, hw_io;
- unsigned int sw_ready, hw_ready;
+ int sw_ready;
+ unsigned int hw_ready;
unsigned int appl_ptr;
unsigned int tram_pos;
unsigned int tram_shift;
