Messages in this thread | | | Date | Sat, 18 Sep 1999 23:26:30 +0200 | From | Peter Enderborg <> | Subject | Re: Bad MIDI performance : 10ms latency instead of the expected 1-1.5ms |
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Benno Senoner wrote:
> On Thu, 26 Aug 1999, Jaroslav Kysela wrote: > > > > I wrote this to measure the MIDI output-to-input delay. > > > I tried both with blocking I/O and non-blocking I/O. > > > Unfortunately I get bad values in both modes: > > > about 11.5ms , and this is exactly the MIDI transfer time (1.3ms) plus > > > 10ms = 1 jiffie. > > > If I run the test on a HZ=1000 kernel I get about 2ms. > > > > MPU401 is very bad hardware for transmit, because it doesn't use interrupt > > to determine that Tx FIFO is free. Some vendors offers large FIFOs > > (8,12,16 bytes), but unfortunately guys at Creative designed SB AWE with > > 2 byte FIFO. > > Hmm .. so you are saying that this is a HARDWARE limitiation ? > How does Windoze manage this ? > > > > > This doesn't explain why your latencies are so big for OSS/Free, because > > OSS/Free code uses polling mode (busy loop for transmit). > > What is the main drawback of this ? > What happens when I send a block of 3000 bytes to the midi device under > OSS/Free ? > A 100% CPU usage for 1sec ? > I can't believe this. > > > > > ALSA uses system timer to avoid busy loop, but the performance depends on > > your HZ value: > > > > 100Hz, 2 byte FIFO = 200bytes/sec > > 100Hz, 8 byte FIFO = 1600bytes/sec > > 100Hz, 12 byte FIFO = 2400bytes/sec > > 100Hz, 16 byte FIFO = 3200bytes/sec > > 200bytes/sec is just rudiculous , how do you plan to drive an external synth > with that little MIDI bandwidth ? > Many songs uses up much of the 3000 bytes/sec bandwidth, especially > when there are many controller/pitchbend events present. > > Do you know if the RX FIFO of the MPU401 has the same problem (no interrupt) or > is there an interrupt present ? > > Is there no other way to make the MIDI response better, without increasing HZ > to 1000 ? > > Does this mean that sequencers running under Windows have the same problems > as we in Linux on the AWE64 ? > Or does Windows a "sane" busywaiting all the time ? :-) > With these big midi delays you can't simply use your PC to act as a midi-tru > box, playing an external synth via masterkeyboard connected to the midi-in. > > > > > Not affected hardware: > > > > GUS soundcards > > AudioPCI chips (ES1370/1371/1373) > > If this is true, then I will throw away my AWE64 and buy an AudioPCI > :-) > > regards, > Benno. > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.rutgers.edu > Please read the FAQ at http://www.tux.org/lkml/
Im the only one that have problems with perfomance while receiving midi data ? It is droping a lot of events. Oss don't drop so mush, but alsa is useless. Is it SMP problem ? Low irq responce times ? I have a SB PCI 128 and a hoontech and have the same problem with both. (The hoontech is only avalible with alsa driver)
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