NXT Links

Here are various external links relevant for programming the NXT brick.

Web sites

GNU ARM: Provides support around GNU tool chains for ARM.
nxt.natulte.net: David Anderson's site, with projects for firmware flashing and a boot monitor.
Volksmikro: A site with a lot of ARM7TDMI development related links, mostly for the Philips LPC microcontroller series.

AT91SAM7S256 Reference Documents

Atmel AT91SAM7S256 documents: The most important document here is the full datasheet for the AT91SAM7S256, which contains information about the peripherals of the microcontroller. Take a look around for some other AT91 related stuff, too. Ignore the ARM stuff here, better get newer versions directly from ARM.
ARM7TDMI Technical Reference Manual: This is the reference manual for the specific processor core version in the AT91SAM7S256. Also contains specific info about JTAG.
ARM Architecture Reference Manual: This book is the basic reference manual for ARM processors. It contains the programmers model and instruction set, in case you need to look at ARM assembly code. You can also pick it up as a PDF file at Altera, look near the bottom of the page. (This might be an older version of the book, does anybody know?)

JTAG

Open On-Chip Debugger: This looks like the most promising open-source project to use for JTAG debugging with the NXT. It seems to support both the wiggler interface and a USB interface from Amontec. It would be nice to extend it to support the Segger SAM-ICE. Here is the project page and an introduction to using it.
JTAG-GDB Server for ARM: This project supports the wiggler among various other parallel port interfaces and looks like it is still active.
GDB Stub for ARMs JTAG interface: A somewhat older project targeted at ARM9TDMI (which seems almost identical to ARM7TDMI except for a longer chain 0), with some nice documentation in german on the home page.
jtagpack: Another GDB interface of about the same age that supports wiggler style hardware.
jtag-arm9: An even older project, but with a nice description how to build a wiggler style JTAG interface.