ISTP (Interrupt Service Table Pointer) register on C6424

Hi Vitor,

Welcome to the E2E forums! Hopefully I can be of help with your first question and get you moving in the right direction.

Vitor de Paulo said:

The problem is: what is the address of this register?

There are a number of CPU core registers which are not actually memory-mapped in the system. Instead, they are accessible only through a special assembly instruction MVC. This is discussed in section 2.8.1 of the 64x+ CPU and Instruction Set manual you referenced (the actual registers are on p34).

Vitor de Paulo said:

Can anyone enlighten this? I´m not that kind of guy that goes at first asking people on forums - I really made my homework and searched for the info., to no avail.

This is a great attitude, and I will reward you with a tip :) The c6x.h header file found in the CGTools install (e.g., C:\CCStudio_v3.3\C6000\cgtools\include) defines all of these registers with C-callable declarations. Once you include this header file you can now access these registers directly. For example, to modify the ISTP you would code out

ISTP = 0x12345678; // But with a real address containing the vector table

BIOS normally does this for you, but it is indeed possible to do without BIOS. Note that the other vital interrupt registers such as IER, IFR (and CSR for the GIE bit) can be accessed this way as well.

I hope that this information helps. I am sorry you had trouble finding this, but if you are interested there is a Submit Documentation Feedback link at the bottom of most PDF files which we use to submit this sort of feedback. Feel free to submit your own suggestions to improve our documentation!