Date   : Fri, 30 Jul 2004 23:23:37 +0100
From   : Sprow <info@...>
Subject: Re: GoMMC and sideways RAM systems

In article <c0snf09e1r70umld3kghmnsggaeojtpvod@...>,
   John Kortink <kortink@...> wrote:

> The GoMMC code writes to the sideways ROM space it's in. Much
> like anything could, were it in a 'standard' RAM bank (as in :
> selected exclusively by ROMSEL).
>
> This presents no problems if ROMSEL is always used to point
> to the read-enabled as well as write-enabled sideways RAM/ROM
> bank. Simple SWRam systems and the Master SWR system use this.

[snip]

> Those who can't live with these two caveats, please steer clear
> from GoMMC. No fix can and/or will be provided.

I can't resist throwing two ideas in
 a) The GoMMC firmware could supply a SRREAD/SRWRITE command (compatible
    with the Master) which does the sideways RAM write properly.

    I can only think that boards like the excellent ATPL allowed the
    ROMSEL bank to differ from the write bank so that they didn't have to
    waste a ROM slot with firmware/supply easy to lose disc programs.
    Since GoMMC uses a slot anyway it's no loss to pop a couple more commands
    into the ROM.

 b) Implement some crazy R-W-W sequence in the CPLD on GoMMC where the 
    driver reads the old contents, writes the byte to the MMC then replaces
    the original byte.

    Oh, hang on, that wont work for a multitude of reasons I've just 
    thought of. Bah.

Sprow.