The SPI flash... SPI means Serial Peripheral Interface and "flash" is a particular type of memory,
capable to be written (and rewritten) in fast mode and able to retain informations even if power
supply is removed, so this kind of memory is part of the "non-volatile" devices.
What's the purpose of SPI flash in our Android Tablet ? It's like the (ancient) floppy disk in old
computers. The floppy, in VERY old computers, was the device containing the Initial Program Loader,
the first program the processor runs to start the whole system. In our tablets, the processor
(I'm speaking about the WM8650, in this case) tries to load a boot program from this device.
The SPI flash memory is small and simple device. Usually has 8 pins (contacts) and isn't
too miniaturized... it's still at "human" dimensions and this is the reason we can remove it
from the circuit, reprogram and resolder it on place. If your tablet is "bricked", you can
immediatly recover, simply restoring a valid boot program in it.
The hardware and the procedures for rewriting the SPI flash have been described in a very good
article :) by me on another page of my site, so, hunt on other pages if interested in, but...
what's stored in the SPI flash of our tablet ?
There are two programs: the W-load and the U-Boot. The U-Boot can execute commands you supply
via serial terminal or you have stored in the microSD, by means of the
wmt_scriptcmd script
file. U-Boot is the tool for handle the very low-level of your tablet. Btw, the NAND flash is
another basic component of your system, 'cause is your device's HARD DISK. As in very old computers,
the floppy loads the system skeleton and then the Hard Disk starts the programs with usual user interface
(or GUI when is Graphical User Interface).
Ok, we turn ON the button, the processor starts, executes the program written in the W-load section.
The U-boot then starts the system that's on NAND memory and you have your tablet working.
When you try to unbrick your tablet rewriting the SPI flash, you MUST use the right version
of U-Boot and W-Load, 'cause if you choose a wrong version, all the process can't start. A VERY
important section (usually don't mentioned) is the W-load program. There is a particular version
for any RAM arrangment in your tablet. Not all the RAMs are the same: even if your "global"
ram size is a certain number of MB, the rams can be arranged in different ways. For different
arrangements, there are different W-loads.
How can I understand what's my specific W-Load ?
You can take a look on the serial output that comes out from your tablet at power on. The serial
interface is a VERY powerful instruments and I highly recommend to you to purchase or build one for
modding and better understanding your tablet.
Look at this example:
WonderMedia Technologies, Inc.
W-Load Version : 0.15.00.01
UPDATE_ID_1_4_4_0_2_256MB_0150001
ethaddr............found
wloader finish
U-Boot 1.1.4 (Aug 24 2011 - 10:14:10)
WonderMedia Technologies, Inc.
U-Boot Version : UPDATEID_0.04.00.00.10
U-Boot code: 03F80000 -> 03FC3190 BSS: -> 03FCD724
boot from spi flash.
SF0: ManufID = 37, DeviceID = 3013 (Missing or Unknown FLASH)
Use Default - Total size = 8MB, Sector size = 64KB
There are some very useful infos: these are W-Load version and UPDATE_ID, U-Boot Version and UPDATEID.
With such informations you can easily "build" your own SPI flash and it will be EXACTLY the one that
fits your tablet. You also have infos on which type of SPI flash is mounted in the tablet. In the
example before, the memory has ID 0x373013 (that is unknown to the system, so it starts with default
values that are good for all memories).
Usually, the SPI flash has 512KB (kilobytes) space, but if you look on the datasheet it's called a
4 megabit memory; that's exactly the same, 'cause 4Mbits = 512KBytes.
In our tablets, the SPI flash memory is divided into 2 areas: the first, starting at address 0x00000
and ending at 0x6FFFF (not fully used) is the U-Boot program; the second, starting at address 0x70000
and ending at 0x7FFFF (almost fully used) is the W-Load program.
I wrote a small program that can build for you the
my-spi.bin file, the BIN file of 512KB you need
to re-flash your SPI memory. The program is written in FreeBasic (under Windows), and doesn't need for
installation. Just decompress the .ZIP you can download
->here<- in a folder,
for example
spi-flash and you have the executable to run.
In order to create your
my-spi.bin file, you need, obviously, for the submentioned files
u-boot.bin and
w-load.bin. So, go to the FirmwareInstall folder of your Uberoid upgrade
folder (or to the same folder of original rom) and copy the u-boot.bin you find there in the new
created folder. For the w-load, you have (often) different file names that all starts with w-load prefix
and finishes with .bin suffix, but the right file is the one has inside the same signature you have read
in the serial terminal (in our example is UPDATE_ID_1_4_4_0_2_256MB_0150001). If you are in doubt,
simply try copying all of them in your new folder and then rename it, one at a time, in
w-load.bin.
The program is "stupid" and looks for input:
u-boot.bin and
w-load.bin and produces as output:
my-spi.bin .
When you start the
buildspi.exe, the program generates the output file AND SHOWS to video the
actual versions of U-Boot and W-Load programs; if some of that versions isn't the one you need for,
simply load another and try again.
Once the file is created and the versions are both identical to the ones you read from serial
terminal at the device boot, you have the right SPI file to program into the chip.
In the picture below, you can have a look to a working program screenshot. Hope this
will help you.
