PM0214 datasheet(242/245 Pages) STMICROELECTRONICS

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Core peripherals

PM0214

242/245

DocID022708 Rev 4

In STM32F4xx devices there is no individual mask and the enable/disable of the FPU

interrupt is done at interrupt controller level.

In STM32F3xx devices in addition to the FPU interrupt controller interrupt mask bit, there is

an individual mask bit for enabling/disabling the FPU interrupt sources (the IXC flag is

masked by default in STM32F3xx devices).

As it occurs very frequently, the IXC exception flag is not connected to the interrupt

controller in STM32F4xx devices, and cannot generate an interrupt. If needed, it must be

managed by polling.

Clearing the FPU exception flags depends on the FPU context save/restore configuration:

•

No floating-point register saving: when Floating-point context control register (FPCCR)

Bit 30 LSPEN=0 and Bit 31 ASPEN=0.

You must clear interrupt source in Floating-point Status and Control Register (FPSCR).

Example:

fpscr_val

= __get_FPSCR();

{ check exception flags }

fpscr_val &= (uint32_t)~0x8F; // Clear all exception flags

__set_FPSCR(fpscr_val);

•

Lazy save/restore: when Floating-point context control register (FPCCR)

Bit 30 LSPEN=1 and Bit 31 ASPEN=X.

In the case of lazy floating-point context save/restore, a dummy read access should be

made to Floating-point Status and Control Register (FPSCR) to force state

preservation and FPSCR clear.

Then handle FPSCR in the stack.

Example:

reg_val =

__get_FPSCR();

//dummy access

fpscr_val=*(__IO uint32_t*)(FPU->FPCAR +0x40);

{ check exception flags }

fpscr_val &= (uint32_t)~0x8F ;

// Clear all exception flags

*(__IO uint32_t*)(FPU->FPCAR +0x40)=fpscr_val;

__DMB() ;

•

Automatic floating-point registers save/restore: when Floating-point context control

Bit 30 LSPEN=0 and Bit 31 ASPEN=1.

In case of automatic floating-point context save/restore, a read access should be made

to Floating-point Status and Control Register (FPSCR) to force clear.

Then handle FPSCR in the stack.

Example:

// FPU Exception handler

void FPU_ExceptionHandler(uint32_t lr, uint32_t sp)

{

if(lr == 0xFFFFFFE9)

{

sp = sp + 0x60;

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