Re: [Qemu-devel] [PATCH 11/22] i8259: Update IRQ state after reset

[Blue Swirl]

On Sun, Oct 2, 2011 at 7:35 PM, Avi Kivity <address@hidden> wrote:
>> >
>> > Can you give an example?  Can be theoretical, doesn't have to refer
>> > to real hardware.
>>
>> For example, outputs A and B should both be driven high by reset.
>> They
>> are connected to a XNOR gate, whose output is fed to edge triggered
>> device. The device should not see any edges outside of the reset
>> cycle, during reset cycle they are ignored.
>>
>
> I don't see the issue?  After phase 1 the two outputs will be high, after 
> phase two they will be whatever the device logic computes.
>
> During phase 1 you may see an edge, but that also happens with real hardware. 
>  The target device my see A and B driven high before it sees the reset pulse, 
> and A and B (and the inputs of the XNOR gate) may have different timings.
>
> The device may see an edge immediately before reset, but then it will be 
> reset itself.

The difference is that on real HW the edge will happen when the reset
line is still active, so it will be ignored.