How to disable/ de-activate FPU on SparkFun Edge board

Development Boards Artemis
1

Hello,

I’m curious if its possible to disable the FPU on the SparkFun Edge board. If so, is there any literature on how to do this?

Thank you!

2

The best information we can offer is to point you toward the datasheet https://cdn.sparkfun.com/assets/c/1/b/7 … 0_10_0.pdf - page 74 mentions a few power modes for the FPU (they refer to it as m4 in the document), but does not mention disabling as far as I can tell

Hope this helps!

3

The FPU can be enabled and disabled by calling the appropriate HAL functions. It may save a tiny bit of power to disable it, but I’m guessing that it is hardly worth the trouble. In any case, here are the HAL calls:

//*****************************************************************************
//
//! @brief Enable the floating point module.
//!
//! Call this function to enable the ARM hardware floating point module.
//!
//! @return None.
//
//*****************************************************************************
void
am_hal_sysctrl_fpu_enable(void)
{
    //
    // Enable access to the FPU in both privileged and user modes.
    // NOTE: Write 0s to all reserved fields in this register.
    //
    SCB->CPACR = _VAL2FLD(SCB_CPACR_CP11, 0x3) |
                 _VAL2FLD(SCB_CPACR_CP10, 0x3);
}

//*****************************************************************************
//
//! @brief Disable the floating point module.
//!
//! Call this function to disable the ARM hardware floating point module.
//!
//! @return None.
//
//*****************************************************************************
void
am_hal_sysctrl_fpu_disable(void)
{
    //
    // Disable access to the FPU in both privileged and user modes.
    // NOTE: Write 0s to all reserved fields in this register.
    //
    SCB->CPACR = 0x00000000                         &
                 ~(_VAL2FLD(SCB_CPACR_CP11, 0x3) |
                   _VAL2FLD(SCB_CPACR_CP10, 0x3));
}
4

Thank you! I’m going to give it a try.

5

This worked. Thank you so much!

robin_hodgson:
The FPU can be enabled and disabled by calling the appropriate HAL functions. It may save a tiny bit of power to disable it, but I’m guessing that it is hardly worth the trouble. In any case, here are the HAL calls:

//*****************************************************************************

//
//! @brief Enable the floating point module.
//!
//! Call this function to enable the ARM hardware floating point module.
//!
//! @return None.
//
//*****************************************************************************
void
am_hal_sysctrl_fpu_enable(void)
{
//
// Enable access to the FPU in both privileged and user modes.
// NOTE: Write 0s to all reserved fields in this register.
//
SCB->CPACR = _VAL2FLD(SCB_CPACR_CP11, 0x3) |
_VAL2FLD(SCB_CPACR_CP10, 0x3);
}

//*****************************************************************************
//
//! @brief Disable the floating point module.
//!
//! Call this function to disable the ARM hardware floating point module.
//!
//! @return None.
//
//*****************************************************************************
void
am_hal_sysctrl_fpu_disable(void)
{
//
// Disable access to the FPU in both privileged and user modes.
// NOTE: Write 0s to all reserved fields in this register.
//
SCB->CPACR = 0x00000000 &
~(_VAL2FLD(SCB_CPACR_CP11, 0x3) |
_VAL2FLD(SCB_CPACR_CP10, 0x3));
}

6

hey,

This development board comes with a power shut off feature, by connecting a pushbutton to the On/Off pin. The 3.3V power supply can be completely disabled by holding the button for five seconds and turned back on by a brief button press.