USB2 patches

[Andrew Thompson]

On Sun, Feb 01, 2009 at 09:40:01PM +0100, Hans Petter Selasky wrote:
> Hi Warner,
> The example is not the best. Let's pick another example:
> 
> Assume you have a 3g modem and we are doing software flow control. Regularly 
> modem status bits are transferred between host and device. Now, lets assume 
> that the modem application has only got one thread. What will happen if 
> transferring the RTS/CTS status bits to the modem is synchronous? Immediate 
> data-loss! Especially at higher data rates.
> 
> Let me elaborate: Assume it takes 3ms to handle a control request to program 
> the DTR/RTS/CTS, because the device is slow. Then you have a 1024 byte buffer 
> on a BULK endpoint which needs to be handled every 1ms. If DTR/RTS and CTS 
> are not done async, you severely degrade the overall performance of the 
> system, don't you agree about that, if every time you update the modem status 
> have to wait 3ms, having to skip Rx'ed data?

As Warner suggested, you would only drain if the previous DTR/RTS/etc
command is still in flight so there is actually no delay.

Say DTR is queued to turn on, its correct to drain this before allowing
a subsequent command to turn it off. To queue this and have a thread
execute a series of on/off/on/off in one go later isnt right IMHO.

Andrew