Lpc2000

bruce_p1 wrote:

>I was searching through this group to see if anyone else was having 
>an unreliable secondary JTAG connection issue with the LPC210x 
>chips; guess I'm not alone.
>
>I too am using a Nohau JTAG debugger; the EMUL-ARM, but that doesn't 
>seem to be the issue.
>
>According to the LPC210x datasheet, to enable secondary JTAG you 
>have to bring DBGSEL or RTCK low to disable primary JTAG pins and 
>ETM, then setup the secondary pins in software.  My original setup 
>was RTCK high and DBGSEL low.  It worked perfectly on some boards, 
>but not on my current board.  Then I tried both pins low with the 
>same results.
>
>After much searching through groups and sites, I found a note from 
>an LPC user that said he had pulled DBGSEL high and RTCK low to fix 
>random LPC210x chips that wouldn't go into secondary JTAG.
>
>This worked perfectly and I could recreate the scenario every time!
>
>I have a question into Philips as to what the real deal is and why 
>this works.  I was wondering if it was a reset or power sequencing 
>issue since I have other boards that don't do this.  Since all the 
>signals are internal to the chip, it sure seems like an issue on 
>random LPC210x chips.
>
>Regardless, I thought I'd pass this along since it seemed to be a 
>hot topic a while back.
>
>  
>

This is a Rev 0 board that I'm building, so far one-of-a-kind (until 
production).  I tie both DEBUG + RTCK low through 10K resistors.   Then, 
I put this in crt0.S:

======= begin ============
start:
_start:
_mainCRTStartup:
      ldr   r0, JTAG2
      ldr   r1, PINSELREG
      str   r0, [r1]
;
========= snip ==========

Variables are defined as:

========= begin =========
JTAG2:
.word 0x55400000
PINSELREG:
.word 0xe002c004
========== snip =========

So far, no problems with JTAG.  I'm daisy chaining with an LPC2138 that 
is first in the chain.

TomW

-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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