[E3-hacking] E3 Memory Map?

Cliff Lawson clawson at amstrad.com
Tue May 16 11:29:45 BST 2006

> -----Original Message-----
> From: Matt Callow [mailto:mc-lists at tesco.net]
> Hmm, I though PBL loaded and executed a block called 'LDR' 
> and then that 
> loaded a block called 'LINUX' ?

Oh yeah, I forgot LDR (I actually split the load that way cos PBL can never
be changed in the field (except we later did!)) but the Linux loading
process was subject to change so I added in a secondary level to the process
so it could be more easily changed than the very risky strategy of changing
the NOR (which risks bricking phones if it screws up!)

So if you had something that you want to load but don't want any of the
PARMS nonsense then just fixup the block of binary with an "LDR" header and
it will be loaded and executed but it is LDR that contains the stuff that
goes hunting for PARMS and then fashions it into the format that Linux likes
to see and then finds LINUX and executes that passing it the parm block. SO
if you want command line parms leaver LDR intact and call the module LINUX

As for size limits that's what MEM is all about, It's a module whose body
only contains a couple of numbers. One is the "end copying here" address and
then other is the "end app, start of adverts" address. At the moment I think
the MEM you have has the first number set to something like just 2MB so the
PBL itself only copies 2MB of NAND out to RAM and then does the search for
LDR within this. LDR then runs and reuses this copied block to search for
PARMS and LINUX (latest, valid versions - there's usually two of each).

So if you can't squeeze the LINUX you want into this space make a new MEM
with a bigger first number so the PBL will copy more or, if MEM is not found
(or just corrupted) the PBL copies 16MB of NAND to flash anyway.

The idea behind MEM was that we were trying to get the "boot to splash
screen" time to be the minimum possible so rather than hard coding copy
sizes in the PBL this allowed us to vary the copy size and fine tune it.


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