JTAG instructions to access the ARM-Cortex-M4 registers

Question

I have a debug probe that allows me to perform JTAG operations (Instruction and Data scans). Having this, I would like to know how do I get to the MCU registers knowing that the SOC I am using implements the JTAG Debug Port defined by the ARM CoreSight Debug Architecture.

My guess is that it would imply to make transactions through the Debug Port, the Access Port, the AMBA AHB bus interface and an IO port from the ARM core. How are these transactions made in terms of IR and DR scans? Where can I find an example?

Answer 1

I'm no expert, but I think the cortex technical reference manuals should have the information you're looking for.

Google search for "cortex m4 technical reference manual", which currently brings up this:

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.subset.cortexm.m4/index.html

For concrete examples, maybe go digging into the openocd project (http://openocd.org)