[U-Boot] FSBBP: uboot Programming on to the flash for MPC8548 for bootup

[JerryVanBaren]

Andy Fleming wrote:
> On Wed, Aug 27, 2008 at 12:16 AM, Ajeesh Kumar <ajeesh at tataelxsi.co.in> wrote:
>> hi sir/madam,
>>
>> I'm using a MPC8548E processor(power pc) also, i've interfaced a nor flash
>> of 128 MB to the processor.
>> i've read few documents and got to know that the uboot.bin should be
>> programmed at 0xfff80000.
>> Also, when i saw the uboot.bin size it was 512K. so, it could fit between
>> 0xfff80000 - 0xffffffff.
>> I 'M USING ABATRON BDI2000/BDI3000 FOR THIS.
>> Now my question is:
>> 1) If i'm making changes(addition/deletion of code) to the bootloader(uboot
>> 1.2) and re compile it, i believe that the size of the uboot.bin will get
>> changed i.e >/< 512K. NOW AT WHICH LOCATION I SHOULD FLASH THE
>> UBOOT.BIN(SIZE IS NOT EQUAL TO 512)
>> FOR Eg.  If my uboot.bin size is >512K ?????
> 
> 
> Well, it's not likely you will change the size of the binary.  You
> see, the 512K size is a result of a quirk of the 85xx platform.  The
> reset vector is at 0xfffffffc, but we define the base address to be
> 0xfff80000, so we fill in the space between, and it's 512K.
> 
> The result is, you don't need to mind the size, unless you grow the
> compiled output by over 200K.  Try to avoid that ;)
> 
> Andy

Hi Andy,

I was looking at the MPC8548CDS config.  The memory map is:
   0xFFF80000 256K - u-boot
   0xFFFC0000 128K - env
   0xFFFE0000 128K - reset vector & bootpage (only one 4K page used!)

Putting the env between u-boot and the reset vector is a horrible thing 
to do.  As a result, the top page of flash is almost entirely unused and 
is very difficult to use.

I have a EP8548 config (whose origins was the MPC8548CDS config) that I 
modified to use this memory map:
   0xFFFA0000 128K - env
   0xFFFC0000 256K - incl reset vector & bootpage

Is there any reason *not* to do this?  (The only downside I can think of 
is that existing boards with the CDS-style map would get their env 
erased when reprogrammed with a revised memory map u-boot, but that is 
easy enough to recover from.)

Best regards,
gvb