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While trying to use Atmel's ASF library, they say

  • __FPU_PRESENT: Initialize macro __FPU_PRESENT = 1 when building on FPU supported Targets. Enable this macro for M4bf and M4lf libraries

So I guess I need to check the datasheet if my uC, ATSAM4S16C AU has a floating-point unit and if so, define the macro before including the header inside my project.

But I can't figure the datasheet. Section 12.4.6 lists entries like

VADD.F32 | {Sd,} Sn, Sm | Floating-point Add

However, no clock cycles indicated. Searching the document for FPU or F32 yields nothing. Checking the instruction, only ADD is documented, no VADD.32. So I do not know if this is computed in hardware or in software (in libm.a).

How do I know if the SAM4 has an FPU?

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  • \$\begingroup\$ Not really sure on this but I think all Cortex-M4 cores have it. But you could probably just try enabling and see if some code involving a fair bit of floating point math actually works. \$\endgroup\$
    – PeterJ
    Commented Feb 3, 2014 at 11:44
  • \$\begingroup\$ No, they don't. It's optional in the M4: infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0553a/… \$\endgroup\$
    – Tom L.
    Commented Feb 3, 2014 at 11:47
  • \$\begingroup\$ @TomL. Thanks I didn't realise that and your answer looks correct. \$\endgroup\$
    – PeterJ
    Commented Feb 3, 2014 at 11:53
  • \$\begingroup\$ Unfortunately the Atmel site doesn't specify FPU as a searchable parameter (which would be nice). \$\endgroup\$
    – Tom L.
    Commented Feb 3, 2014 at 12:39

3 Answers 3

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According to this graphic no FPU is available on the SAM4 S family. Yet, the SAM4 X family should have it.

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  • \$\begingroup\$ So let's see how much is going to speed up my floating point calculations using ASF's arm_math.a instead of the standard libm.a, on a CPU without FPU. \$\endgroup\$
    – Vorac
    Commented Feb 3, 2014 at 11:54
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According to the official device webpage from microchip, there is an FPU available.

Also, the __FPU_PRESENT macro on SAM4SD32C is set. To answer your original question, you can check with this snippet:

#ifndef __FPU_PRESENT
#warning "no FPU!"
#endif
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Here is a list of Atmel SAM4 MCUs, some of which have an FPU. You want a Cortex-M4F architecture, not a Cortex-M4. The SAM4S does not have an FPU.

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