Re: RCM3900/RCM3910 memory map

On 8/7/2012 10:06 AM, Ian Lovatt wrote:
>
> We are designing a board based on the RCM3910 module and have a
>  question regarding memory configuration. Any help with this would be
> greatly appreciated.
>
>  
>
> As we understand the RCM3900/RCM3910 can be run at high speed (44MHz)
> with program code copied from flash to a fast SRAM chip at boot time
> or without the clock doubler and execute code directly out of flash.
> When operating in high speed mode it looks like the bios sets up
> memory quadrants with only 256k of the normal RAM (which is 512k in
> total) accessible. It looks like it would require us to alter the bios
> ourselves if we wanted to make ALL the 'normal' RAM available whilst
> executing at 44MHz ie. No flash mapped in- 2 quadrants mapped to
> program code in 'fast' SRAM and the other 2 mapped to normal RAM.
>
> Can anyone confirm this? Has anyone had any experience in making this
> modification or customising the rabbit bios libs in general?
>

The RCM3900 (and 33xx, 32xx modules) have 768k of RAM. 512k of fast RAM
and 256k of battery-backed RAM.

The bios copies the flash to fast RAM and maps it to the lower 512k, The
battery-backed RAM is mapped at the 512k address (0x80000). The upper
256k is mapped to flash so it can access the user and ID block.

So, all the RAM is available. xmem should be available from the end of
your code in fast RAM to the top of the bbram.

-- 
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     Scott G. Henion, Consultant
Web site:    http://SHDesigns.org
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