Lpc2000

I know a few people have had the secondary JTAG working, but a lot 
have also struggled, so I post this with the hope of helping a few 
people.

Firstly, the assembly code in the Philips App Note is wrong, but will 
perhaps still work.I will take this up with Philips. I shall post the 
code I used on the download area. The two things the Philips code
does 
wrong are:
* Does not set up exception vectors properly.
* Does not do anything after the pin matrix is set up. This could 
cause a crash (exception) which could disturb the JTAG state (perhaps)
.
I set up things pretty much according to the Philips app note, but 
then needed to do the following to get things working:

* You should not reset the device under debugger command unless it 
lets you run the code for a while. The reason for this is that the 
flash code must run to set up JTAG2. Instead, the debugger should be 
configured to stop the running code. 

* THe clock speed needs to be low enough. The JTAG interface can only 
be clocked at up to 1/6 of the core clock. Therefore if you have a 
10MHz crystal you don't want to be clocking much faster than 1MHz. 
Some debuggers let you initialise at one speed, then use a faster 
speed after initialisation. It might be worth adding the PLL speed up 
to the startup code to use a faster JTAG clock.

-- Charles