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

From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH 11/22] i8259: Update IRQ state after reset
Date: Wed, 28 Sep 2011 22:38:24 +0100

On 28 September 2011 19:42, Blue Swirl <address@hidden> wrote:
> We also assume that the reset states of devices and their outputs are
> coherent i.e. the output of one device during reset would not change
> the state of another device from its reset state.

This seems a very dubious assumption to make. Consider the
realview board: the 'card present' line from the pl181
MMC card controller is wired up to (1) a GPIO input on the
'sysctl' system register module [which causes it to appear
as a status bit in a register] and (2) via an inverter to
an input on a pl061 GPIO module. On coming out of reset
something has to be done to make the reset value of the
output from the pl181 be reflected in the internal status
of the sysctl and pl061 devices.

(On real hardware this happens when the pl061/sysctl
devices come out of reset and sample their input pins.
If we wanted to model it that way we'd need internal state
on all gpio lines and a two phase "enter reset"+"leave reset"
or something.)

-- PMM

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