Compiler/TMS570LS3137: Double-precision float in interrupt environment

Tyler Middleton

Part Number: TMS570LS3137

Tool/software: TI C/C++ Compiler

We've come across an issue in our hercules design (TMS570LS3137) where some of our double-precision floating point calculations are giving invalid results.

There are frequent interrupts in our design and our current best guess for what's happening is that a context switch during a double-precision operation, corrupting the result.

I was under the impression this processor supports double-precision natively, so this shouldn't happen. Is there some other explanation? Do we need to manually save FPU state during a context switch somehow?

Thanks for any help you can give!

over 6 years ago

0 Sunil Oak over 6 years ago

TI__Mastermind 49120 points

You have to save and restore the FPU registers. See this thread for an example:

https://e2e.ti.com/support/microcontrollers/hercules/f/312/t/700651

Regards,

Sunil

0 1138 over 6 years ago in reply to Sunil Oak

Expert 1226 points

Hello Sunil,

Will TI's ARM compiler handle the saving and restoring of FPU registers automatically if the INTERRUPT #pragma ( or __attribute__((interrupt)) ) is used for an interrupt handler function written in C?

--thx

0 Sunil Oak over 6 years ago in reply to 1138

TI__Mastermind 49120 points

That is correct. A function required to be an interrupt service routine must be assigned a pragma that indicates that it is an IRQ handler. For example, for an rtiCompare0Interrupt() handler:

#pragma CODE_STATE(rtiCompare0Interrupt, 32)
#pragma INTERRUPT(rtiCompare0Interrupt, IRQ)

In that case if the compilation options include support for the FPU, then the floating point unit registers will be saved and restored automatically by the callee function code generated by the compiler.

Regards,

Sunil

Arm-based microcontrollers

Arm-based microcontrollers forum

Compiler/TMS570LS3137: Double-precision float in interrupt environment