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Subject: Rockbox won't start from flash, any ideas?
From: idc-dragon_at_gmx.de
Date: 2003-06-25


Hello,

frequent readers of this may know that I'm working on getting to Rockbox
start from flash memory, kicking out the original firmware. The reward will be a
much faster "On"-to-music time. Irony has it that I have one of the few
boxes with the wrong flash chip, not in-system programmable. But a new one is on
order, I'm desperately waiting for it.

Meanwhile I have built my toolchain for UART boot (requires the serial mod).
With a little extra hardware mod (pulling the LCD lines low instead of high)
I can exploit a mode where the boot ROM expects code from the UART. A PC
application now transfers a little monitor program to the internal RAM. When
that's done the two can talk, the current command set allows memory read/write
and jumping to an address.

This is sufficient to program the flash (even if completely garbled, because
UART boot comes before flash boot) and other tricks. Currently I'm
"practicing" to start Rockbox. To do that, I use the monitor to configure the DRAM
controller in the same way the flash boot does. When I have the DRAM available,
I load the rockbox binary into place and jump to it.

Expectedly, this didn't really work. The big difference is that I "cold
start" rockbox, with no firmware running ahead of it. In the normal case, Rockbox
is loaded into an environment where "the bed is already made", the firmware
has already initialized much of the hardware.

All it currently does is switching on the backlight for a few seconds, then
shutting it off again. No splashscreen, no harddisk activity. A bit
disappointing. Does this ring a bell to anybody, what initialization might be missing?

My next plan is to use my toolchain to not load rockbox, but the gdb stub.
That can in turn load a debug version of rockbox and allows to step around
there. However, my past experience with gdb (under Windows) is no good. The
target connection was very unreliable, the debug application was often frozen and
had to be killed. Is anybody debugging the box under Windows? Maybe I can
persuade a Linux guy with gdb to do the UART boot mod?

So long,
Joerg

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