[U-Boot] BDIxxxx and others...

[Jerry Van Baren]

David Hawkins wrote:
>> I see you guys talking about BDI3000 and I decided to ask a related
>> question.
>>
>> Those who happen to own MPC8548CDS or something like this know it comes with
>> a small box called CodeWarrior USB TAP.
>>
>> It is supposed to work with their software one has to pay for. I never used
>> anything but GCC suite for anything GCC supports and always tried to avoid
>> commercial tools like a plague. So I want to ask if somebody knows if there
>> are any free tools for that thing...
>>
>> Not that I really need it for something but it is sitting in the box
>> gathering dust and it would be nice ot somehow put it to do something...
> 
> I've wondered the same thing. But didn't manage to find
> anything out there. I've got three ... in the boxes
> the Freescale MDS boards came in.

Yup, got a handful myself.

> The USB-TAP has a PowerPC processor in it ... so even if you
> had to blow away the original firmware, I'm sure it wouldn't
> be too hard to figure out what code would be required to
> make the device look like a USB debugger, and then create
> a set of USB commands to generate JTAG transactions.

MPC866PVR133A in the one I disassembled.  Not a top-of-the-line 
processor, but plenty for the job.

> I think the main problem is getting the JTAG TAP codes
> for manipulating JTAG. I've never seen a document relating
> to that, so they are obviously NDA.

Yup.

> That being said, a weekend with a logic analyzer on a
> BDI2000 JTAG connection would probably give you all the
> info you need to figure out the appropriate JTAG
> commands.

The problem is that it is going to be different for every processor 
family and it may even change between processor revisions.  There is a 
risk that, if you send the wrong sequence, you will damage your target 
processor (JTAG+BSDL can burn up chips too if you set outputs to 
fighting - DAMHIKT).

With a large number of internal registers (many unknown) all hooked 
together into a single scan chain, it will take quite a bit of effort to 
hit each register individually to correlate the scan chain to the register.

Oh, and you need to purchase a commercial debugger to do this, at which 
point you've already spent your money, got your functionality, and lost 
your incentive.

> I've wired up the COP connection on my board via an FPGA,
> so that I could conceivably use the PowerPC JTAG via
> PCI. However, its the lack of open documentation on the
> JTAG commands that has limited my interest in pursuing
> this. However, it would be simple to use that interface
> to log all JTAG transactions, to figure out all the
> JTAG TAP instructions.

The *JTAG* commands *ARE* documented and you can download the BSDL 
(Boundary Scan Description Language) files for all chips that I've 
looked at.  This is *NOT* the internal proprietary "COP" scan chain - 
that just piggybacks on the JTAG/BSDL documented scan chain.  The 
boundary scan allows you to wiggle the external pins on the processor... 
e.g. you can drive an address + data + CS*, toggle the WR* pin, and 
viola, you are programming flash (lots of pain glossed over).

I've looked at UrJTAG
   <http://www.urjtag.org/>
but have not gone further because I already spent the money for a BDI 
;-).  I typically use the BDI for debugging for a few hours on board 
bring up (requires a good board design to start with - thanks, hardware 
guys!).  After that, the only reason I need the BDI is to recover from 
loading bad bits into flash.

The UrJTAG software + JTAG hardware + BSDL file would allow me to 
reprogram my flash for a lot less than the cost of a full JTAG debugger. 
  This is where the USB-TAP support would be Really Nice.

This would also work for the "burn & learn" method - if you are lucky 
and smart (in that order), it can be effective.  Unfortunately, "burn & 
learn" falls into the CompSci category of halting problems:
   <http://en.wikipedia.org/wiki/Halting_problem>

> Cheers,
> Dave

Best regards,
gvb