[U-Boot-Users] Re: (Newbie) MPS8272ADS image layout

Yuli Barcohen yuli at arabellasw.com
Sun May 23 11:28:43 CEST 2004

>>>>> Ward C Travis writes:

    Ward> Forgive me if I have overlooked something simple.  I have
    Ward> compiled u-boot using 'config_MPC8272ADS' and, following
    Ward> Wolfgang's advice, modified as little as possible. I accepted
    Ward> all the defaults, providing no overrides on the make line.

    Ward> Looking at he .srec file, it appears that the image is to be
    Ward> loaded at 0xfff00000 . The configuration words are based there
    Ward> and _start is placed beyond them, at the image + 0x0100 .

    Ward> The ADS board I am working with has the standard 8MB flash
    Ward> SIMM, which when the board boots from flash is mapped
    Ward> beginning at 0xff800000.

    Ward> I am unclear on how the MPC8272 reset vectors the PC to
    Ward> 0xfff00100. Perhaps the simple question is, should the image
    Ward> be loaded into flash at some other address?

The U-Boot must be loaded at the address for which it's built
i.e. 0xFFF00000. It will start running from 0xFFF00100 because the CPU
is "told" to do so by hard reset configuration word (HRCW), and it does
not matter what the flash start address is. Chapter 5 of MPC8272
reference manual would help.

    Ward> My flash is clear - it is a rented board - and so there is no
    Ward> previous loader or configuration words in flash; hence I must
    Ward> boot from EEPROM

No, you don't (and must not). This board provides three possible sources
for the HRCW: BCSR (the CPLD), flash and EEPROM. Unless somebody erased
first sector of the flash, there should be HRCW, but the most reliable
way is to use BCSR: it can't be erased. Unfortunately, it uses high boot
(0xFFF00100) and not low boot as it should be for such big flashes (more
than 1MB). This is the reason the U-Boot is built by default to start at
0xFFF00000. You should not change the jumpers to boot from EEPROM
because then CS0 will be mapped to EEPROM and the flash (containing the
U-Boot) will be unmapped. Please note that the HRCW which you see at the
beginning of the U-Boot image won't be used at all because these
addresses can't respond to first four bus transactions.

    Ward> and download the code (with Metrowerks, via parallel) while
    Ward> flash is remapped for EEPROM boot.  I currently am
    Ward> experimenting with programming the image at various offsets
    Ward> from the beginning of flash. But once I reconfigure to boot
    Ward> from flash and power-cycle, of course, I see no sign of
    Ward> activity.

 Yuli Barcohen       | Phone +972-9-765-1788 |  Software Project Leader
 yuli at arabellasw.com | Fax   +972-9-765-7494 | Arabella Software, Israel

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