So far, attempts to downgrade from 1.5 to 1.0 have been hampered by the fact that nobody is quite sure of dumping the entirety of the 1.0 rom, and the impossibility of creating valid DATA.PSAR from the resulting files.
I'd like to propose a way round this.
In this thread :-
http://forums.ps2dev.org/viewtopic.php?t=1646
"loser" states that a device "lflash:" exists. It's a read/write block device giving full access to all 32mb of flash ram.
What's to stop someone writing an app that dumps 1.0 firmware block-by-block to a single file, and another app that writes the firmware file back to a 1.5 PSP?
This would avoid the problems of missing files that we suspect are evident in all previous attempts to dump 1.0 firmware, as the whole lot is dumped into one file, regardless of its contents. It also avoids the DATA.PSAR problem as we're flashing the unit ourselves, not with Sony's updater.
Now admittedly, simply proposing this is a bit like jerking off. I understand that this forum is for real results, not pipe-dreams.
Ah, who am I kidding, hall of shame here we come.....