Re: Endian Mapping

[Dimiter Popoff <tgi_earth@yahoo.com>]

Amit Shah,

>Does this type of approach work ?
>Does this really solve big endian to little endian mapping ?

Basically yes. Bit 31 is what the MSB is called in a little-endian
(bitwise) notation, bit 0 is what the MSB is called in a big-endian
notation. It is just the same. 

CBE 3:0 refer to byte arrangement. The above would be valid in his case
if he calls his internal MS-byte enable BE-0; how the command is multiplexed
with this would probably not be an issue. 

When it comes to actually reading and writing data through the
bus so configured, you may be pretty sure there will be
surprises with exchanged bytes; but no serious problem, since
the PPC has separate load/store instructions for little-endian
access (which implies he may have to do software fixes to the end
system).

I had some experience recently with a q-span bridge, which could
be programmed for big/little endian byte addressing, a b69030
display controller which had such features (even on a 16-bit
basis), and an 8240 PPC which could also reverse everything.
Quite a mess at the first glance, yet everything could be programmed
to work smoothly.

Dimiter

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Dimiter Popoff
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