TMS320F28377D: EALLOW in ST1

Hi Vincenzo,

Let me check with SW team on this query. Somebody from TI will get back to you soon.

Best Regards,

Nirav

Hi Vincenzo,

Here is a sample C function that will save ST1 to the global variable "savedst1":

uint16_t savedst1;

void read_st1()
{
    asm(" PUSH AL");  // Save AL on stack
    asm(" PUSH ST1");  // Save ST1 on stack
    asm(" POP AL"); // Move ST1 into AL
    asm(" MOV DP, #_savedst1"); // Setup DP for global variable
    asm(" MOV @_savedst1, AL"); // Move ST1 value into global variable
    asm(" POP AL"); // Restore AL
}

Thanks,

Ashwini

hi Ashwini,

Is this also possible with a return parameter, i.e. without a global variable?
Perhaps with the detour of a local variable.
Or does the compiler do unpredictable things in this regard?

thanks again

KR

Vincenoz

Hi Vincenzo,

Since local variables are placed on stack its not possible to have embedded assembly reference local variables. It may be better to have a C callable assembly code that returns the value of ST1 to keep the code robust and free from any compiler optimization effects.

Information on how to create C callable assembly function can be found at:

Compiler Guide

https://www.ti.com/lit/spru514

Assembler Guide

https://www.ti.com/lit/spru513

The C2000Ware also has library functions written in assembly and those can also be used as reference. Example DCL library.

Thanks,

Ashwini

Hi,

so I did:

static uint16_t GetEallow()
{
    asm(" PUSH ST1");
    asm(" POP AL");
    asm(" AND AL, #0060h");
}

But I get: warning #994-D: missing return statement at end of non-void function "GetEallow".
This is correct, but I cannot use a return-C-statement in this case, neighter a asm(" LRETR"); is working.

What can I do?

Gerd

Hi Gerd,

I have reached out to the compiler team to find out and will get back to you soon.

Thanks,

Ashwini

Hi Gerd,

Please see section 7.5 "Interfacing C and C++ With Assembly Language" section. It has guidelines on writing assembly functions. Sub-section 7.5.2 shows how to write an assembly function and have that be called by the C code and return a value. It would be better if the GetEallow is written as assembly function.

Compiler Guide

https://www.ti.com/lit/spru514

Thanks,

Ashwini

Works fine:

    .global _GetEallow
_GetEallow:
    PUSH    ST1
    POP        AL
    AND     AL, #0060h
    LRETR

with

if ( 0 == GetEallow() )
...

Thanks a lot.

Gerd

I hardly tried to do that, but I cannot find this function.

Gerd

Hi Gerd,

Since Vincenzo created the post, I believe only he can mark it as resolved. I will go ahead and close the thread at my end.

Thanks,
Ashwini