[wdmaudiodev] Re: USB Audio Using Interrupt Transfers
- From: "vrf" <vrf@xxxxxxxxxxxx>
- To: <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Sat, 21 Jun 2003 13:50:47 +0800
> Udo Eberhardt write:
>> Due to slight variations of audio clock and USB clock, you need to use a
>>larger FIFO size than 8 anyway.
You mean 8 bytes?
But my chip (MC68HC908JB8/MC68HC08JB8/MC68HC08JT8-Rev. 2.0) only have 8
bytes In/Out buffer. Maybe I need choose another chip.
Besed on your discussion, for matching 64kbps Codec speed I think:
If I use a usb chip with 8 bytes In/Out data buffer and 1ms interval, it
may loss 8 bytes data when not be polled in. And this may occur every 2...10
secs. This tone may be not good.
If I use a usb chip with 16 bytest In/Out data buffer and 1ms polling
interval, it may not loss any data. This tone will be good enough.
If I use a usb chip with 32 bytest In/Out data buffer and 2ms polling
interval, it may not loss any data. This tone will be good enough.
If I use a usb chip with 64 bytest In/Out data buffer and 4ms polling
interval, it may not loss any data. This tone will be good enough.
In normal, Host will fetch data of half of the max packet size. When any
frame not be polled in, the next polling will fetch data of max packet size.
Am I right?
The second question, I found that in Windows 2000 Sound Recorder's menu:
"File"-->"Properties"-->Format Conversion --> "Convert now"-->Attributes
8.000kHz, 8bit, Mono 7kb/sec
7kb/sec means 7K Bytes/sec?
if so, why it is not 8kb/sec?
Thank you all!
----- Original Message -----
From: "Udo Eberhardt" <Udo.Eb@xxxxxxxxxxx>
To: <wdmaudiodev@xxxxxxxxxxxxx>
Sent: Friday, June 20, 2003 7:18 PM
Subject: [wdmaudiodev] Re: USB Audio Using Interrupt Transfers
> Yes, you are right. To be precise the situation is as follows:
> When the input buffer is full and the host controller switches to a new
> buffer then there will be a USB frame in which you will not be polled.
> At least this is true for the UHC.
> So, I would recommend to use 2 ms or 4 ms polling interval.
>
> Due to slight variations of audio clock and USB clock, you need to use a
> larger FIFO size than 8 anyway.
>
> Udo Eberhardt
> Thesycon GmbH
>
>
> bart@xxxxxxxxxxxxx wrote:
> > vrf wrote:
> >
> >
> >>>Transferring an audio stream by an interrupt pipe should be possible.
> >>>However, it is somewhat "unusual".
> >>>The priority of interrupt transfers is higher than bulk transfers. The
> >>>host controller will poll an interrupt endpoint once per USB frame, if
> >>>the polling interval is 1 ms.
> >>>
> >>
> > I found that XP does *not* poll the interrupt endpoint always as
requested
> > by the polling interval bInterval member). Once in a while (2..10 secs)
it
> > skips a poll so you will be needing a larger outputbuffer (at least).
> >
> > Bart
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