[Libre-soc-dev] Programming a PPC440EPx via JTAG

[Luke Kenneth Casson Leighton]

On Tue, Oct 12, 2021 at 1:56 PM Cesar Strauss <cestrauss at gmail.com> wrote:

> The JTAG protocol, apparently undocumented and proprietary, was
> reverse-engineered, and seems to have:
>
> 1) a command for uploading and executing a single Power instruction,

interesting!

> 2) a debug SPR that can be read and written into,
> 3) a debug mode register, for doing reset, halt, run, etc.
>
>  From that, higher-level operations can be performed, like reading and
> writing to registers, SPRs, memory, PC, etc.

yehyeh.  makes sense, that basically allows literally anything to be
done, you can create your own debug system from it.

DMI is a little more sophisticated :)

l.