Using JTAG to debug the OMAP3 port

My JTAG kit arrived today, so I’ve had a quick play with it. The good news is that it works, and it’s easy to use CCS to connect to the board and start debugging it without having to launch any code through CCS itself. The bad news follows :)

• It’s a bit slow, although as the cheapest JTAG kit on the market that’s basically what I was expecting. I believe the more expensive emulators are meant to be faster.
• You can’t halt the ARM core while it’s in a WFI instruction. Although that’s easy to fix just by removing/killing the Portable module.
• The debugger isn’t quite as fully-featured as I was hoping (e.g. I couldn’t find any way to view memory by physical address)
• The debugger’s also a bit unstable – it crashes whenever I try opening the ETB view. I believe there is some magic I need to do first to enable the ETB (or enable access to it – I’ve tried running the “enable ETB access” script with no success), so hopefully once I’ve read all the docs I’ll be able to make use of the ETB
• I can see most/all of the OMAP’s hardware registers in the register list, but not their values (just 0×0BAD0BAD, etc.). Perhaps it’s because the debugger doesn’t like the MMU being on.
• You can load symbols from .out and .x files, but not AIF or GPA files (not that I was really expecting support for those!). Hopefully it will be possible to get something working using the plugin or scripting systems.

Once I’ve had a chance to play with it some more I’ll probably put up a wiki page containing a guide on how to do everything. But if anyone else wants to get started, just be aware that if you order the USB100v2 from Direct Insight you need to use the comments box to request the model D version (BH-USB-100v2D) because the older version lacks a ribbon cable and is too big to connect straight to the beagleboard. Update: The USB100v2D now has its own page on Direct Insight’s shop here

No wiki page yet, but here are a couple more things I’ve learnt today:

• If you reset the beagleboard using the physical reset button, the debugger will lose its connection. Instead, you want to select the Target → Reset → System Reset option from within the debugger.
• The memory save option measures the save length in 4 byte words; the “Type-size” option has no bearing on the length. In fact it’s probably best to leave “type-size” as 8 bits, since when I tried saving with a 32bit size everything was byte swapped (although that could obviously be fixed by using the “swap” option). Type size and byte swapping doesn’t seem to have any affect on transfer speed either (The transfer speed seems to be a measly 256 bytes/sec – I told you it was slow!)

Another fun oddity:

• As mentioned in the first post, viewing the hardware registers doesn’t work. And as theorised, this is because CCS doesn’t like it when the MMU is on
• This MMU phobia causes problems because the .gel files set up a memory map telling the debugger which regions it can & can’t access, which access widths to use when accessing them, etc. So today when I tried looking at some memory in the RMA the debugger wouldn’t let me, until I edited the omap3530_cortexA8.gel file to turn off the memory map.

I think the next time I want to use CCS I’ll try downloading the latest v5 beta and see if they’ve fixed this yet (and if not, bitch about it on their forums). Plus setting up the new version will allow me to do a proper “getting started” guide for the wiki.