Hi Ruben,
Am 30.08.2010 um 20:22 schrieb Ruben Viets:
> Hi Nikolaus,
>
> I am looking forward to the results and documentation of your jtag setup.
Unfortunately the PCBs are overdue...
> I have below questions with respect to jtag and jz4730:
> - Where to attach the jtag interface connections to the jz4730 (trendtac) ?
> Maybe the hidden usb port or ttyS0 serial port ?
According to the schematics, there should be a 24 pin ZIF "Test Connector". On
the Letux 400 it is called J500 and located
just behind the 4-pin RS232 connector. I will publish some more details (and
Photos) on that as soon as the PCB is finished.
> - What kind of Jtag access serial protocols/testmodes are needed for jz4730
> (trendtac epc700) ?
Basically, JTAG is JTAG.
But the difference is what all the bits in the CPU are doing. As far as I know
there is some EJTAG standard for
MIPS - but we will see.
> - do we need additional software for jtag communication to be able to program
> nandflash with uboot ?
Yes.
Basically, all the flipflops of the CPU are connected into a long shift
register so that you can read/write all bits
in the CPU through JTAG. Therefore, one can write into the PC, into address
registers etc. And into the instruction
register. So it is possible to inject commands to control the memory interface
and to single-step instructions
neither stored in RAM or Flash...
So what we need is hardware to control this shift register process from a host
computer (this is my adapter and
the Openmoko debug board which carries a USB-to-JTAG adapter chip from FTDI).
And software to do something useful with the hardware remote control
connection. As far as I have analysed
yet, there is OpenOCD but focussed on ARM processors.
> - Is there a possibility to 'heal' bad nand blocks via jtag commands ?
I don't think so. As far as I understand, you can't access the NAND *better*
than through CPU commands.
JTAG gives remote control over the CPU and only indirectly to NAND.
best regards,
Nikolaus
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