Details - hardice

submited by
Style Pass
2021-06-08 02:00:07

How Probe Mode works for the P6 is simple. To halt the processor, the engineer asserts the PREQ# pin on the CPU. The CPU then replies by asserting PRDY#. The engineer submits x86 instructions one at a time to the Probe Instruction Register using the WRSUBPIR TAP command. Using these instructions, he can write registers, memory and access I/O devices.

To read registers and memory, he has to shift the data he needs to read to the EAX register. Subsequently he issues a RDMSR to the PDR MSR. He then executes the READPDR TAP command to read the PDR out of the JTAG shift register.

The author admits that this article is not comprehensive. If you have anything to add or contribute, please post your contributions in the comments below.

Leave a Comment