USB isochronous traffic with Rasberry Pi [WAS: Re: USB audio device on Raspberry Pi]

[Ian Lepore]

On Mon, 2014-05-05 at 08:18 -0700, Adrian Chadd wrote:
> evil idea:
> 
> #define DELAY(ms) _DELAY(ms, __FILE__, __LINE__)
> 
> .. then modify the relevant arm delay function to take FILE/LINE and
> KTR log it. :-)
> 
> 
> -a

Except some uart console output routines are structured like

    while (!readreg(STATUS) & TXRDY)
        DELAY(n);

I don't know why people think that calling delay in busy loops like that
has any value, considering that DELAY is almost always implemented as
some form of

    while (readreg(COUNTER) < target_count)
        ;

I guess maybe it has value only in that it helps you find busy-loops.
I'd rather that we had a function just for that purpose, like

    while (readreg(COUNTER) < target_count)
        cpu_busy_loop();

(We have something like that that's x86-specific, iirc).

-- Ian