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Date: Tue, 13 Dec 2011 16:22:05 +0000
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From: Peter Maydell <peter.maydell@linaro.org>
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Subject: Re: [Qemu-devel] [PATCH v3 12/14] hw/sd.c,
 hw/sd.h: add receive ready query routine to SD/MMC API
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To: Evgeny Voevodin <e.voevodin@samsung.com>
Cc: m.kozlov@samsung.com, Mitsyanko Igor <i.mitsyanko@samsung.com>, qemu-devel@nongnu.org, d.solodkiy@samsung.com

On 13 December 2011 15:11, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 12 December 2011 06:43, Evgeny Voevodin <e.voevodin@samsung.com> wrote:
>> From: Mitsyanko Igor <i.mitsyanko@samsung.com>
>>
>> Data transfer direction between host controller and SD/MMC card is selected by
>> host controller configuration registers, but whether we actually need or need
>> not perform data transfer depends on type of last issued command. To avoid
>> memorization of which type of command host controller issued the last time, we
>> can use simple query procedures, to make sure that SD/MMC card is in the
>> right state. The only query routine currently presented in SD/MMC card
>> emulation is sd_data_ready(), this patch adds sd_receive_ready() routine.
>
> I've thought about this a bit more and spent some time poking through
> the standards docs. I'm kind of suspicious of both this function and
> the existing sd_data_ready(). Real hardware doesn't have these signals,
> both ends of the sd-controller-to-card connection just do their thing
> and trust that the other end is in the state it is supposed to be.
> If you (in the controller model) don't already know whether you are
> OK to send/receive data then you haven't modelled some part of the
> controller's state properly.

Having thought even more :-), sd_data_ready() is actually modelling a
real hardware behaviour: "have we seen the start bit on the data line?".
So it is justifiable. I still don't think sd_receive_ready() is, though.

-- PMM