TMS320C6657: Save B3 in C++ code

David Pardessus

Part Number: TMS320C6657

Hello,

For debugging purpose of a design in customer configuration (no jtag access), I need to get and log the return address of a C++ method (compiler 8.3)

So, I'd like to save B3 register (if I've understood the calling convention) and give it as parameter to another method.

The problem is I don't known how to use __asm statement to interact with the C++ method

Regards,

David

over 3 years ago

0 Rajarajan Uthayakumar over 3 years ago

TI__Expert 4314 points

Hi David,

Let me understand the issue. Do you want to access/store the return value of the "_asm" statement which reads the value on the "B3" register?

Thanks,

Rajarajan U

0 Rajarajan Uthayakumar over 3 years ago in reply to Rajarajan Uthayakumar

TI__Expert 4314 points

Hi David,

To access the control register, please use the "cregister" keyword as mentioned in the "C6000 compiler user guide (7.4.2)" on page 150 and explained with their code usage.

Also to interface Assembly code with C/C++ code refer to page 200 on Topic "7.5 Interfacing C and C++ With Assembly Language". It will give an overview, and also register conventions for "Data Path Register B (Register File B)" are mentioned on Page 196 "7.3 Register Conventions".

//register access code
extern cregister volatile unsigned int B3; 
main() 
{ 
    printf("B3 = %x\n", B3); 
}

Thanks,

Rajarajan U

0 David Pardessus over 3 years ago in reply to Rajarajan Uthayakumar

Intellectual 290 points

Hi Rajarajan,

I'm using compiler 8.3 so I use sprui04d.pdf. There is a chapter 7.5.3 The __cregister Keyword but I understand that Ax and Bx are not control registers. This seems to be confirmed by my c6x.h which list the same creg as the document.

Regards,

David

0 Rajarajan Uthayakumar over 3 years ago in reply to David Pardessus

TI__Expert 4314 points

Hi David,

Reading the B3 register using the above code might work. Kindly check into this.

Thanks,

Rajarajan U

0 David Pardessus over 3 years ago in reply to Rajarajan Uthayakumar

Intellectual 290 points

Hi Rajarajan,

It seems that it does not work : main.cpp, line 19: error: unrecognized cregister name 'B3'

Regards,

David

0 Rajarajan Uthayakumar over 3 years ago in reply to David Pardessus

TI__Expert 4314 points

Hi David,

Will check with the code and EVM. Will provide an update ASAP.

Thanks

Rajarajan

0 Rajarajan Uthayakumar over 3 years ago in reply to Rajarajan Uthayakumar

TI__Expert 4314 points

Hi David,

The above example did not work, I apologize for the mess.

While going through the following thread I found out, since "B3" is preserved by the child.

https://e2e.ti.com/support/tools/code-composer-studio-group/ccs/f/code-composer-studio-forum/309988/question-about-register-usage-in-c-called-assembly-code-for-c6000

https://e2e.ti.com/support/tools/code-composer-studio-group/ccs/f/code-composer-studio-forum/427115/call-a-assembly-function-directly-from-a-member-method-of-c-class

Rajarajan Uthayakumar said:
Also to interface Assembly code with C/C++ code refer to page 200 on Topic "7.5 Interfacing C and C++ With Assembly Language".

As mentioned in this document, the following ways we can interface Assembly and C++ programs to get values from the register "B3".

Using the "Extern "C" " keyword, functions declared in the Assembly code.
Import variables from assembly code.
Import constant from Assembly code.

Thanks,

Rajarajan U

0 Rajarajan Uthayakumar over 3 years ago in reply to Rajarajan Uthayakumar

TI__Expert 4314 points

Hi David,

We can read the registers from CCS.

I will attach the "Hello world" project to read the registers. Will experiment and add the "asm" functions for reading "Core" registers. 8345.helloWorld.zip

Thanks

Rajarajan U

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TMS320C6657: Save B3 in C++ code