zboot-rom-mmcif.txt

ROM-able zImage boot from MMC
-----------------------------

An ROM-able zImage compiled with ZBOOT_ROM_MMCIF may be written to MMC and
SuperH Mobile ARM will to boot directly from the MMCIF hardware block.

This is achieved by the mask ROM loading the first portion of the image into
MERAM and then jumping to it. This portion contains loader code which
copies the entire image to SDRAM and jumps to it. From there the zImage
boot code proceeds as normal, uncompressing the image into its final
location and then jumping to it.

This code has been tested on an AP4EB board using the developer 1A eMMC
boot mode which is configured using the following jumper settings.
The board used for testing required a patched mask ROM in order for
this mode to function.

   8 7 6 5 4 3 2 1
   x|x|x|x|x| |x|
S4 -+-+-+-+-+-+-+-
    | | | | |x| |x on

The zImage must be written to the MMC card at sector 1 (512 bytes) in
vrl4 format. A utility vrl4 is supplied to accomplish this.

e.g.
	vrl4 < zImage | dd of=/dev/sdX bs=512 seek=1

A dual-voltage MMC 4.0 card was used for testing.