no TRST help!

Development Boards MicroMod
1

Hi,

I have a unit with ARM Xscale PXA255 processor. This box has jtag pins. However the pins available are VCC, TDI, TDO, TCK, TMS, and GND.

Is there any way that I can get olimex wiggler working without TRST?

I remember I read a post from some forum saying I can put the Xscale into debug mode if I can set TCK low, and TDI & TMS high.

Any help would be appreciated.

Thanks.

2

For debugging a PXA255 you’ll need both nTRST and nSRST. The debugger needs to be able to individually assert both reset lines. If you just want to flash, e.g. using the openwince jtag tools, then having no reset could work.

Regards,

Dominic

3

Thanks for the reply Dominic.

Debug would be nice, but flashing the flash is my concern for now.

I’ve borrowed an expensive jtag emulator, but this thing won’t allow me to write into flash unless I have trst pin hooked up.

I saw jtagkey-tiny which lists it supports “open drained trst”.

I’m not sure what it means by supporting “open drain”.

4

Amontec JTAGkey or Amontec JTAG-Tiny allow the TRST_N and SRST_N signals to be tristated (drive ‘0’, drive ‘1’, open-drain).

When open-drain, the ‘1’ MUST be fixed by an external pull-up (pull-up on your target board), and the ‘0’ will be drive by the JTAGkey buffer.

For OpenOCD you have to use in the configuration file:

reset config [combination] [trst-type] [srst-type]

  • is one of none, trst_only, srst_only or trst_and_srst.

  • [combination] is one of srst_pulls_trst, trst_pulls_srst, combined, separate.

  • [trst-type] is one of trst_open_drain, trst_push_pull.

  • [srst-type] is one of srst_push_pull, srst_open_drain.

Laurent

http://www.amontec.com