On Tue, 3 Feb 2015 21:18:54 -0700 Simon Glass sjg@chromium.org wrote:
(What does FEL stand for?)
That's a good question. I believe that it might be based on the "jump to fel" message from the console output of the Allwinner's BOOT0 bootloader: http://linux-sunxi.org/FEL#Serial_output
Other than this, I don't know what this name stands for.
In fact the FEL code has a special entry point at 0xffff0020, which is the target of this "jump to fel" action in BOOT0: https://github.com/hno/Allwinner-Info/blob/master/BROM/ffff0000.s#L9
It initializes the USB hardware again, and I believe that this is the reason why I have some problems trying to use this method. So far the flow looks like this:
1. The SPL is uploaded to SRAM and executed (to initialize DRAM) and other things. 2. As the last step in the SPL ('return_to_fel' in your code), we just transfer control directly to 0xffff0020 instead of using the address from the lr register. 3. The USB stack in my PC seems to be a bit confused by the MBUS hardware re-init. For example, the next "fel ver" command fails for me with a timeout. However the follow up fel commands work fine, and I can successfully "write" and "exe" the main u-boot binary.
The incomplete demo patch for the fel tool has been posted at http://lists.denx.de/pipermail/u-boot/2015-February/204024.html
This is an attempt to make sunxi's FEL code fit with the normal U-Boot boot sequence instead of creating its own.
Most of the FEL special-case code is removed, although I may have gone too far with my changes to generate a u-boot-sunxi-with-spl.bin file even when FEL is enabled. This may not be possible since the MMC stack makes SPL too large for FEL anyway, although it may be possible for other boot mediums.
This is actually very good.
If we can resolve the jump to 0xffff0020 problems (try to perform a clean USB shutdown before doing this?), then the SPL size limitation for USB booting is gone and we get a unified SPL binary for both SD card boot and boot over USB. With no need for a lot of special sunxi things in the U-Boot boot sequence. I'm going to have another look at it today in the evening to see if the remaining problems can be resolved.
This series is available at u-boot-dm, branch sunxi-working.
Thanks a lot for this work.