Help with JTAG
marcin.mielczarczyk at gmail.com
Thu Jan 31 06:14:20 UTC 2013
On Mon, Jan 28, 2013 at 7:34 PM, <teslarode at yahoo.com> wrote:
> I've found a very interesting article about SciphoneDream G2 published on
> your webpage at http://bb.osmocom.org/trac/wiki/SciphoneDreamG2 that
> covers pretty detailed information about MT6235 SoC, bootstrapping as well
> as JTAG. This is the only article I have ever found on internet about MTK
> SoC and JTAG.
What I am trying to accomplish is to access NAND flash and write to it over
> JTAG (in order to recover from corruption after bad flash) on MTK8555 SoC
> which according to my in-depth research and analysis has very similar
> architecture to MT6235. If I can't write to NAND over JTAG but would be
> able to launch u-boot that would be a solution too. I am very good at ARM
> assembly and debugging, however I am not very experienced with JTAG. Do you
> think you (or anyone else) could help me out, by giving me guidance what
> hardware, software, config files should I use to make JTAG work on this SoC
> ? Any help or advise would be more then appreciated!
For JTAG debugging of MT6235 I used commercial debugger Trace32 from
Lauterbach. I know that it was also working with OpenOCD.
In case when your NAND is corrupted completely it can be pretty hard to get
your board running. The biggest problem is in initialising SDRAM/DDR RAM
controller, to get external RAM working.
When I had MT6235 running (booting without issues), I was able to break
running processor and load my code into external RAM as RAM was already
initialised by bootloader.
Later on when I learnt Mediatek boot process and new where bootloader is
placed in NAND, I extracted SDRAM initialisation procedure. NAND layout is
described in the link you mentioned.
MT6235 had static RAM (64KB or 128KB) available from start (without
initialisation), and you could place your code for SoC init there (this is
where DRAM initialisation was copied from NAND and then executed).
I have never flashed NAND using JTAG on MT6235 as I haven't found it
useful. I focused on getting U-Boot running and this is the first place
which has flash driver for NAND found on Sciphone G2.
In case of any further questions you can contact me directly as this group
covers different topics.
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