Re: [LAU] Replacing/enhancing MIDI, and OSC

Hanspeter Portner wrote:
> On 16.02.2015 18:36, Harry van Haaren wrote:
>> No, the MIDI "cable" baud rate is 31250, while MIDI over USB runs
>> at 112500.
>
> Where do these 112500 Baud come from?
> Just curious...
>
> Does this refer to low-speed USB-MIDI (e.g. 1.5Mbit/s)?

USB MIDI must use bulk transfers, which are not allowed for low-speed
devices.

> high-speed USB has a maximal packet size for bulk transfers of 512
> bytes, I'm not sure though whether this applies to USB-MIDI, too?

512 is the _only_ allowed value for the maximum high-speed bulk packet
size, so every high-speed device must be able to handle such packets.

>> -Bandwidth: lots better than DIN-cable MIDI, but limited
>
> Depends on underlying USB speed, I guess

While MIDI over DIN is asynchronous, USB bulk transfers have an implicit
throttling mechanism, i.e., a packet transfer is not complete until the
device has chosen to accept it. This means that the bandwidth is just
as high as the device can process the data. USB/MIDI interfaces cannot
run faster than DIN cable speed, and there might be devices where the
USB interface has been duct-taped onto an existing MIDI interface. (And
the really stupid MFM0860 chip is _slower_ than 3125 bytes/s.)

Regards,
Clemens
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Received on Tue Feb 17 12:15:02 2015