CCS/TMS320F28388D: wrong XAR register value with lib function pow or powf

HS FAE Germany

Part Number: TMS320F28388D
Other Parts Discussed in Thread: C2000WARE, TMS320F28377D

Tool/software: Code Composer Studio

Hello,

use:
lib: rts2800_fpu32_fast_supplement.lib
lib: rts2800_fpu32_fast_supplement_eabi.lib
compiler: ti-cgt-c2000_20.2.0B1 / ti-cgt-c2000_18.1.1.LTS

Customer had a problem with the lib function pow or powf.
Description (in assembler):
Target addresses and parameter addresses are writen into the XAR register. These are not reloaded later before reading or writing of this register. Then the powf function is used. But the XAR register values aren't automatically saved onto the stack. The powf function uses some XAR register (eg XAR2) and overwrites these register. There are the wrong addresses in the XAR register after execution of the powf function and the following code uses the wrong values or jumps to the wrong addresses.

Attached is an example screenshot. I can send the code or what else you need offline.

Regards, HolgerCompiler Library Fehler FPU-Funktion.docx

over 5 years ago

0 Richard Poley over 5 years ago

TI__Mastermind 27200 points

Holger,

Yes, please send me whatever you have, either in a post or offline, whichever is easier. I'm not able to reproduce the issue just with the information in the doc. Also, please let me know to CCS and tools versions involved. Many thanks.

Regards,

Richard

0 HS FAE Germany over 5 years ago in reply to Richard Poley

TI__Mastermind 32420 points

Hello Richard,
I will ask for the sources. Should they send it in following format?

How to Submit a Compiler Test Case

Regards, Holger

0 Richard Poley over 5 years ago in reply to HS FAE Germany

TI__Mastermind 27200 points

Hi Holger,

Yes, please do it this way. Thanks.

Regards,

Richard

0 Daniel Bernhard (Schindler) over 5 years ago in reply to Richard Poley

Prodigy 10 points

Hi Richard,

By chance I stumbled over exactly the same problem and the problem is actually very trivial.

The problem is within the rts2800_fpu32_fast_supplement library v2.01.00.00 and affects the functions "pow" and "exp" (This is part of the C2000Ware package: C2000Ware_2_01_00_00\libraries\math\FPUfastRTS\c28\)

Both of the mentioned functions (implemented in assembler) use the registers XAR1 and XAR2 but don't restore the original value of that register.

Relevant sections of "pow":

;;*****************************************************************************
;; Register Usage:
;;   XAR0: pointer to the lookup table | R0H : x, base
;;   XAR1: pointer to the exp coeffs   | R1H : y, exponent
;;   XAR2: storing the lookup tabe index
;; Stack Usage:
;;
;;   |_______|<- Stack Pointer                    (SP)
;;   |_______|<- LF_X_EXP_U                       (SP-1)-----> Local Frame
;;   |_______|<- LF_ABS_X_H                       (SP-2)    |
;;   |_______|<- LF_ABS_X_L|LF_ABS_X|LF_X_MANT    (SP-3)----
;;   |_______|<- R4H                              (SP-5)
;;   |_______|<- rpc calling function             (SP-7)
;;
;;*****************************************************************************

[...]

;;-----------------------------------------------------------------------------
;; Context Save
;;-----------------------------------------------------------------------------
    ; The stack pointer is aligned to an even address by the calling function
    MOV32    *SP++,R4H
    ADDB        SP, #LF_SIZE        
;;-----------------------------------------------------------------------------

[...]
    MOVL        XAR1, #_FPU32expTableCoeff
[...]
    MOV32        XAR2, R4H            ; 1|   ACC = sizeof(float)*x_i
[...]
    MOV32       R4H, *--SP           ; 1|   restore R4H
[...]
    LRETR

Now to quote the compiler reference (SPRU514P), Chapter 7.3.2 point 1:

If the called function modifies XAR1, XAR2, or XAR3, it must save them, since the calling function assumes that the values of these registers are preserved upon return.

As it is easy to see, the function only store register R4H but it should additionally store XAR1 and 2 as well.

0 Richard Poley over 5 years ago in reply to Daniel Bernhard (Schindler)

TI__Mastermind 27200 points

Thank you for the report. I understand and will ask for someone to look into this and get back to you.

Regards,

Richard

0 Richard Poley over 5 years ago in reply to Richard Poley

TI__Mastermind 27200 points

Holger, Daniel,

Thank you both for reporting this - it is indeed a bug. The fix to push and pop those two registers is straightforward, however we have missed the window to update it in the next C2000Ware release, so it will be 2Q before we're able to get a fix into the public version. In the interim, you can edit the assembly module yourselves and rebuild the library. For licensing reasons I am not allowed to attach the modified file, but I can describe how to change it.

In C2000Ware, the file pow_f32.asm is located in directory: \libraries\math\FPUfastRTS\c28\source\fpu32

You'll need to add the following lines:

Below line 118, add two instructions to save XAR1 & XAR2:

MOV32 *SP++,R4H
PUSH XAR1
PUSH XAR2
ADDB SP, #LF_SIZE

Then, below what is now line 248, add two lines to restore these tow registers:

ADDF32 R2H, #1.0, R2H ; *|
POP XAR2 ; 1| restore XAR2
POP XAR1 ; 1| restore XAR1
MOV32 R4H, *--SP ; 1| restore R4H

Save this file. You'll then need to re-build the library, which you can do by opening the CCS project located in directory: \libraries\math\FPUfastRTS\c28\ccs\fpu32

I think this is everything but let me know if you run into any issues. Thanks again for reporting this issue.

Regards,

Richard

0 Richard Poley over 5 years ago in reply to Richard Poley

TI__Mastermind 27200 points

I should add that a similar bug exists in the expf() function and will also be addressed in the next C2000Ware release.

Regards,

Richard

0 Scott Osborne over 5 years ago in reply to Richard Poley

Prodigy 100 points

We are also having an issue with the powf() function sometimes not returning the correct value when calculating the following:

AdjustedThrottle = powf(ThrottleValue, 1.20);
AdjustedThrottle *= 0.398;

The correct value is returned when the JTAG programmer first flashes the TMS320F28377D and runs the code from CCS (using Free Run).

If the power to the processor board is cycled (i.e. standalone Boot to Flash mode) incorrect values are returned.

We have tried re-compiling the FPUfastRTS library but the compiler complains about a missing 'make' file so have not been able to test if this is the problem.

Do you think our powf() function problem is related or something else.

Can you help us compile the FPUfastRTS library?

Regards,

Scott

0 Richard Poley over 5 years ago in reply to Scott Osborne

TI__Mastermind 27200 points

Scott,

If it's working with the debugger connected it doesn't sound like an algorithm problem. More likely it's either the FPU tables in the wrong place or an uninitialized variable. Please check p.15-16 in the library user's guide about placement of the tables. Also, can you check 'ThrottleValue' before the call to powf to be sure it's what you expect?

To rebuild the library, you should be able to open the following project in CCS:
C:\ti\c2000\C2000Ware_2_01_00_00\libraries\math\FPUfastRTS\c28\ccs\fpu32

Then, in the 'General' section of project properties, select the 'Configuration' to either EABI or COFF, and re-build. Is this what you're doing?

Regards,

Richard