Division crash on DM647 (FastRTS)

The result of that division would be a subnormal number; apparently the fastrts64x.lib library can't handle a subnormal division result.  This library is not a product of the compiler team; we need to move this thread to a forum where this library is supported.

Please see the following post: http://e2e.ti.com/support/embedded/bios/f/355/p/166716/698820.aspx#698820.

Does your issue still occur when you use float values as opposed to doubles?

Jason Reeder

Hi Jason,

Thanks for your reply.

I cannot come up with a test case that crashes when only using floats.

Note that the DSP is not producing an inaccurate or incorrect result; it crashes!   It exits with an NMI.  I hope you guys can look into this.

Thanks in advance.

Hello

The double division is a bug in the FastRTS library 1.42. Use 32 bit floats as a workaround.

Thanks

Elush Shirazpour

Thanks for your response. However, we cannot take a large code base that makes liberal use of double-precision arithmetic and simply use single-precision instead. This would undoubtedly cause an important loss of precision in some calculations, resulting in subtle bugs that would take months to fully discover.
 
More likely, we will have to cease using FastRTS, which will result in unfortunate performance degradation.
 
As this issue clearly highlights a critical flaw in the FastRTS library, and is easily reproducible, can you not simply fix it? This issue may cause occasional DSP crashes for anyone who unwittingly uses the double-precision support provided by this library.

Gerte

What stack are you using on your DM647? Is it the EDSDK or RDK stack?

Elush Shirazpour

Can you clarify what you mean with EDSDK / RDK?

Gerte

Are you using a TI stack?

And also...

http://e2e.ti.com/support/embedded/bios/f/355/t/252281.aspx

To reiterate, we are using:

• Code Generation tools V6.0.18
• DSP/BIOS 5.32.01.05
• CCS3.3 / SR 7.67
• FastRTS 1.42

The division crash occurs in the context of a DSP/BIOS task.

Beyond that, we don't know what you mean by "TI stack".  As far as we can tell, the terms "EDSDK" and "RDK" do not appear in our platform documentation. Please clarify.

Hello Gerte

There are no scheduled FastRTS library for the DM647 at this moment. The double division crash will have to be avoided with the workaround we mentioned earlier.

Thank you

Elush Shirazpour

Hello,

We are still trying to solve this problem. Using the assembly source code included in the FastRTS installer, we pinpointed the root cause of the crash. 

Line 1160 of fastrts62x64x.src reads:

  [A1]   shru  .s1   A5,A0,A5       ; H1 = H1 >> Y
||[!B1]  zero  .l1   A5:A4          ; ans = 0 if biased exp = 0 (underflow)

If A1 is true and B1 is false, these pipelined instructions both use register A5.  This results in an NMI.

A possible and safe fix is to not pipeline the instructions.

Can you guys please provide us with a new release of FastRTS that includes this fix?  This saves us from modifying your code and risking undesired side effects, including possible license violations.

Thanks a lot.