• Locked Locked
  • Replies 7 replies
  • Subscribers 119 subscribers
  • Views 11420 views
  • Users 0 members are here
2025 survey

We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.

Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Cortex M4 FPU against fixed point math

michele corradin
Note: This was originally posted on 1st March 2012 at http://forums.arm.com

Hi,
I'm working on 3 cortex, a STM32F027, cortex M3, a TI Cortex M4 and an Infineon Cortex M4.
I would like to move from a TI C2000 TMS320F2810 (fixed point 32bit core) to an M4 to control a 3 phase power bridge.
My algorithms nowadays work in fixed point math, IQ22, and are based for 98% on simple multiplications and some sine/cosine calculations: PI, PID, Pll, low pass filter, notch, ..
I ported the algorithm in the cortex mainly redifining the IQmpy, moltiplication, and the IQsin, sine calculation first in fixed point then in floating point.
I was expencitng to have a speed improvment running in floating because every multiplication in fixed math requires a shift while in floating I don't need the shift but I'm exeriencing a dramatic slow down of the algorithm running in floating point.
I'm doing my test in IAR.
I checked the assembler and I verified the compiler is using the floating point.
My only explenation is that the FPU doesn't have, as far as I know, direct access to the CPU registers so every multiplication in FPU requires 2 loads to the FPU registers and another load to move the result to the CPU register.
Is there anybody that can confirm me that?
Thank you very much
michele
Parents
  • Note: This was originally posted on 1st March 2012 at http://forums.arm.com

    dear joseph,
    I'll post a couple of example with the assembler.
    In my case I'm completely switching all my code from IQ22 to float and I verified it is using the floating point.
    Let's me make a "simple" question: is it true that the FPU doesn't have direct access to the core registers so to perform an operation in the FPU I have to load the data from the CPU registers to the FPU and back?
    I check the manual but I'm not sure if I understood right: in the assembler it seems to me to see some load operations.
    Thank you very much for your help
    michele
Reply
  • Note: This was originally posted on 1st March 2012 at http://forums.arm.com

    dear joseph,
    I'll post a couple of example with the assembler.
    In my case I'm completely switching all my code from IQ22 to float and I verified it is using the floating point.
    Let's me make a "simple" question: is it true that the FPU doesn't have direct access to the core registers so to perform an operation in the FPU I have to load the data from the CPU registers to the FPU and back?
    I check the manual but I'm not sure if I understood right: in the assembler it seems to me to see some load operations.
    Thank you very much for your help
    michele
Children
No data