[Libre-soc-bugs] [Bug 499] Create experimental gdb protocol implementation in nmigen for debugging

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Thu Sep 24 19:24:57 BST 2020


--- Comment #6 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #5)
> (In reply to Jacob Lifshay from comment #4)
> > 
> throwing away Staf's JTAG io work, and the fact that he has SVF scan files
> already done, which can be run against the simulator, verilator, FPGA *and
> the ASIC* this is a huge saving all of which we throw away and have to do
> ourselves to replicate it in gdb serial?

I'm not saying we should completely replace JTAG, I'm saying we could and also
that GDB's protocol is nicer for debugging and requires less pins.

> > One of the nice features of GDB's protocol is it supports debugging
> > multi-threaded programs (we would interpret gdb's threads as processor
> > cores). I don't know if the jtag protocol supports that.
> both serial and JTAG are single resource and immediate response.  any multi
> threading is done at the software level (as part of gdb)

My point was that gdb's protocol already has built-in handling for things like
"send a signal (interrupt) to thread #7" or "read registers from thread #5" or
"pause thread #1" or "resume thread #2". This will be useful for later chips
that have multiple cores, since we'd just tell gdb that a chip with 4 cores has
4 gdb-visible threads.

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