Re: [Qemu-devel] high resolution timer question

[Anthony Liguori <anthony@codemonkey.ws>]

Blue Swirl wrote:
> On 12/10/07, Robert Reif <reif@earthlink.net> wrote:
>   
>> Writing data to a serial port on the sparc emulation happens immediately.
>> I would like to throttle the write speed to match the actual baud rate.
>> What's the best way to do this in qemu?  Will QEMUTimer work for a
>> 1 millisecond timer?
>>     
>
> Do you mean that you want the serial port to match the host speed so
> that for example, at 9600 baud, target would only receive 9600 bits
> per second? Or do you mean that the emulated CPU should see bits
> arriving at the same rate that the real CPU would see compared to CPU
> execution speed?
>
> On the positive side, this would fix a bug with serial interrupts
> arriving too fast which can trigger Linux panics. But this would also
> complicate the design because currently the devices do not need to
> emulate any internal buffers.
>
> I think the throttling should be done at CharDriver level so that all
> targets and also other devices, like parallel ports (SUNW,bpp anyone?)
>   

But the timing is entirely a concept of the hardware devices.  It seems 
like it would be easier to just add a growable buffer, and then setup a 
timer in each device that reads from the buffer.

Regards,

Anthony Liguori

> can benefit. It should be turned off when talking to real hardware on
> the host.
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