* need help diagnosing USB MIDI latency problem with MPD16
@ 2010-09-14 23:36 Krzysztof Foltman
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From: Krzysztof Foltman @ 2010-09-14 23:36 UTC (permalink / raw)
To: alsa-devel
[-- Attachment #1: Type: text/plain, Size: 2457 bytes --]
Hello,
Some time ago, I wrote the Akai MPD16 protocol handlers (input/output)
for the USB MIDI driver. Unfortunately, the kernel driver seems to
suffer from a rather embarrassing input latency, it looks like the MIDI
event timing granularity is >100ms (so the latency is variable, making
the pad practically useless except if a rhythm is played with the rate
matching the polling rate!). At the same time, a simple Python based
contraption using libusb and bulkRead in a while loop, gets much better
results. The same USB MIDI driver in the same kernel and PC doesn't have
noticeable problems with class-compliant E-Mu Xboard25 connected to the
same USB port.
Both devices use endpoints in bulk mode. I've attached the excerpts of
lsusb -v output for both devices - the only differences are:
1) the Akai device isn't class compliant,
2) the E-mu device has one pair of inputs/outputs, the Akai has two
(control/configuration and MIDI proper)
3) the maximum packet length is 32 for E-mu, 64 for Akai.
When I enabled logging in midi.c (#define DUMP_PACKETS), it looks like
the device is returning data packets rather infrequently, as a single
packet often contains multiple events (up to 3) when two pads are
pressed in rapid succession. So, it looks like a problem outside of my
snd_usbmidi_akai_input.
One thing that *does* help, though, is disabling the 'control' port by
adding endpoints[0].in_cables = 0; in Akai quirk handling in
snd_usbmidi_create - when input from the control port is not polled, the
choppiness disappears completely. I'm guessing that the device itself
(or something in between) has some problems having to handle the URBs
for both endpoints, and that perhaps the IN/NAK exchange on a "control"
endpoint causes the device's microcontroller (or something else?) to
stall for a while. However, in that case, a proper solution (one that
doesn't involve sacrificing the ability to use control port for
configuration) would involve submitting URBs for the control input
endpoint only when control port is open on ALSA side, and cancelling
them when the port is closed. However, that sounds pretty invasive.
Any hints? The device in question is rather uncommon and hasn't been
supported for a while, so refactoring the whole USB MIDI driver to
accommodate it doesn't sound like a great idea - but still, the latency
thing sucks pretty bad for a drumming-oriented device!
Thanks in advance,
Krzysztof
[-- Attachment #2: xboard.usb --]
[-- Type: text/plain, Size: 4746 bytes --]
Bus 005 Device 003: ID 041e:3f00 Creative Technology, Ltd
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 1.10
bDeviceClass 0 (Defined at Interface level)
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
idVendor 0x041e Creative Technology, Ltd
idProduct 0x3f00
bcdDevice 0.47
iManufacturer 1 E-MU Systems, Inc.
iProduct 2 E-MU Xboard25
iSerial 3 E-MU-62-3F00-07D60505-90185-98
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 101
bNumInterfaces 2
bConfigurationValue 1
iConfiguration 0
bmAttributes 0xc0
Self Powered
MaxPower 250mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 1 Control Device
bInterfaceProtocol 0
iInterface 0
AudioControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 1 (HEADER)
bcdADC 1.00
wTotalLength 9
bInCollection 1
baInterfaceNr( 0) 1
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 1 Audio
bInterfaceSubClass 3 MIDI Streaming
bInterfaceProtocol 0
iInterface 0
MIDIStreaming Interface Descriptor:
bLength 7
bDescriptorType 36
bDescriptorSubtype 1 (HEADER)
bcdADC 1.00
wTotalLength 37
MIDIStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (MIDI_IN_JACK)
bJackType 1 Embedded
bJackID 1
iJack 0
MIDIStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (MIDI_IN_JACK)
bJackType 2 External
bJackID 2
iJack 0
MIDIStreaming Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 3 (MIDI_OUT_JACK)
bJackType 1 Embedded
bJackID 3
bNrInputPins 1
baSourceID( 0) 2
BaSourcePin( 0) 1
iJack 0
MIDIStreaming Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 3 (MIDI_OUT_JACK)
bJackType 2 External
bJackID 4
bNrInputPins 1
baSourceID( 0) 1
BaSourcePin( 0) 1
iJack 0
Endpoint Descriptor:
bLength 9
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0020 1x 32 bytes
bInterval 1
bRefresh 0
bSynchAddress 0
MIDIStreaming Endpoint Descriptor:
bLength 5
bDescriptorType 37
bDescriptorSubtype 1 (GENERAL)
bNumEmbMIDIJack 1
baAssocJackID( 0) 1
Endpoint Descriptor:
bLength 9
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0020 1x 32 bytes
bInterval 1
bRefresh 0
bSynchAddress 0
MIDIStreaming Endpoint Descriptor:
bLength 5
bDescriptorType 37
bDescriptorSubtype 1 (GENERAL)
bNumEmbMIDIJack 1
baAssocJackID( 0) 3
Device Status: 0x0000
(Bus Powered)
[-- Attachment #3: akai.usb --]
[-- Type: text/plain, Size: 2678 bytes --]
Bus 005 Device 006: ID 09e8:0062 AKAI Professional M.I. Corp.
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 1.10
bDeviceClass 255 Vendor Specific Class
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 8
idVendor 0x09e8 AKAI Professional M.I. Corp.
idProduct 0x0062
bcdDevice 1.00
iManufacturer 1
iProduct 2
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 46
bNumInterfaces 1
bConfigurationValue 1
iConfiguration 3
bmAttributes 0xa0
(Bus Powered)
Remote Wakeup
MaxPower 100mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 4
bInterfaceClass 255 Vendor Specific Class
bInterfaceSubClass 0
bInterfaceProtocol 255
iInterface 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 1
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 1
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x02 EP 2 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 1
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x82 EP 2 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 1
[-- Attachment #4: akai.py --]
[-- Type: text/x-python, Size: 1907 bytes --]
import usb
import alsaseq
mpd16 = None
idVendor = 0x09e8
idProduct = 0x0062
for bus in usb.busses():
for device in bus.devices:
if device.idVendor == idVendor and device.idProduct == idProduct:
mpd16 = device
break
if mpd16 is None:
raise ValueError, "No MPD16 found"
conf = mpd16.configurations[0]
iface = conf.interfaces[0][0]
midiept = None
for ept in iface.endpoints:
if ept.address == 0x82:
midiept = ept
break
if midiept is None:
raise ValueError, "MIDI endpoint not found"
dev = mpd16.open()
dev.setConfiguration(mpd16.configurations[0])
dev.claimInterface(0)
dev.setAltInterface(0)
#dev.reset()
#print "MPD16", dir(mpd16)
#print "Config", dir(conf)
#print "Iface", dir(iface)
#print dev.getString(2, 200)
#print midiept.maxPacketSize
alsaseq.client("MPD16", 0, 1, False)
while True:
data = dev.bulkRead(midiept.address, midiept.maxPacketSize, 0)
if len(data) == 2:
continue
pos = 0
while pos < len(data):
elen = data[pos] - 32
edata = data[pos + 1 : pos + 1 + elen]
channel = edata[0] & 0x0F
if edata[0] >= 0x90 and edata[0] <= 0x9F:
if edata[2] > 0:
alsaseq.output( (alsaseq.SND_SEQ_EVENT_NOTEON, 1, 0, 253, (0, 0), (0, 0), (0, 0), (channel, edata[1], edata[2], 0, 0)))
else:
alsaseq.output( (alsaseq.SND_SEQ_EVENT_NOTEOFF, 1, 0, 253, (0, 0), (0, 0), (0, 0), (channel, edata[1], 0, 0, 0)))
if edata[0] >= 0xA0 and edata[0] <= 0xAF:
alsaseq.output( (alsaseq.SND_SEQ_EVENT_KEYPRESS, 1, 0, 253, (0, 0), (0, 0), (0, 0), (channel, edata[1], edata[2], 0, 0)))
if edata[0] >= 0xB0 and edata[0] <= 0xBF:
alsaseq.output( (alsaseq.SND_SEQ_EVENT_CONTROLLER, 1, 0, 253, (0, 0), (0, 0), (0, 0), (channel, 0, 0, 0, edata[1], edata[2])))
pos += 1 + elen
dev.releaseInterface()
[-- Attachment #5: Type: text/plain, Size: 160 bytes --]
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2010-09-14 23:36 need help diagnosing USB MIDI latency problem with MPD16 Krzysztof Foltman
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