nRF54L15: high current consumption after using FPU, need information about FPU_IRQn interrupt vector.

[Frank Viganske]

Hi,

i am working on a project using the nRF54L15.

Hardware: custom board with nRF54L15

Software:

• Wirepas SDK (1.6.2) 
• nrfx drivers (version 3.9.0) with some customization to integrate it into the SDK
• CMSIS DSP floating point libraries (Version 5.1)

I see in my current measurements that idle current increases by roughly 300µA after using the floating point unit. I already checked the developer zone for any similar tickets, and there are lots of them, though all are for other SoC, like nRF52 series. 

Most of these tickets suggest the high current consumption comes from unhandled FPU interrupts. I was already able to confirm that this is indeed the reason for the increased current. Now i'm trying to implement a solution for this.

The suggested solution from other tickets is to do something like the code below:

__STATIC_INLINE void pwr_mgmt_fpu_sleep_prepare(void)
     {
        uint32_t original_fpscr;

        CRITICAL_REGION_ENTER();
        original_fpscr = __get_FPSCR();
        /*
         * Clear FPU exceptions.
         * Without this step, the FPU interrupt is marked as pending,
         * preventing system from sleeping. Exceptions cleared:
         * - IOC - Invalid Operation cumulative exception bit.
         * - DZC - Division by Zero cumulative exception bit.
         * - OFC - Overflow cumulative exception bit.
         * - UFC - Underflow cumulative exception bit.
         * - IXC - Inexact cumulative exception bit.
         * - IDC - Input Denormal cumulative exception bit.
         */
        __set_FPSCR(original_fpscr & ~0x9Fu);
        __DMB();
        NVIC_ClearPendingIRQ(FPU_IRQn);
        CRITICAL_REGION_EXIT();

        /*
         * The last chance to indicate an error in FPU to the user 
         * as the FPSCR is now cleared
         *
         * This assert is related to previous FPU operations 
         * and not power management.
         *
         * Critical FPU exceptions signaled:
         * - IOC - Invalid Operation cumulative exception bit.
         * - DZC - Division by Zero cumulative exception bit.
         * - OFC - Overflow cumulative exception bit.
         */
        ASSERT((original_fpscr & 0x7) == 0);
     }

That is, 1. clear the FPU exception bits in FPSCR, 2. clear the pending IRQ with NVIC_ClearPendingIRQ(FPU_IRQn);

Which brings me to my problem. I can't find any definition for FPU_IRQn for the nRF54L15, neither in the Nordic Documentation nor in any of the processor header files.

For other SoCs FPU_IRQn is defined as an enum value in IRQn_Type. For the nRF54L15, in nrf54l15_application.h there is a similar type definition for IRQn_Type, but it does not contain the FPU_IRQn.

Maybe it is just named differently? 

So my question is: how do i clear the pending IRQ for the FPU on the nRF54L15?

Best regards

Frank Viganske