SW-EK-TM4C1294XL: FPU Enable/disable on reset

Pranav Saraswala

Part Number: SW-EK-TM4C1294XL
Other Parts Discussed in Thread: TM4C1294NCPDT, EK-TM4C1294XL

Hi,

I see in datasheet of TM4C1294NCPDT page 145 that FPU is disabled on reset.

Also on page 247 of SPMU298E, it says that "If a floating-point instruction is executed when the floating-point unit is disabled, a NOCP usage fault is generated."

In view of above, when i follow lab07 of CLP workshop of eval board EK-TM4C1294XL, that uses floating point operations, without enabling FPU anywhere in code; it works fine on my eval board.

There is something i am missing, or i misunderstood. Please help me to set-right my understanding.

BR,

Pranav.

over 7 years ago

0 Charles Tsai over 7 years ago

TI__Guru**** 190806 points

Hi,
Can you check if your compiler configuration disable code from being generated that utilizes the FPU?

0 Pranav Saraswala over 7 years ago in reply to Charles Tsai

Intellectual 435 points

Hi Charles,

Thanks for response.
I understand that FPU support is enabled. My compiler flag setting reads as below:

-mv7M4 --code_state=16 --float_support=FPv4SPD16 -me --

0 Chester Gillon over 7 years ago in reply to Pranav Saraswala

Guru 92251 points

Pranav Saraswala said:
My compiler flag setting reads as below:

-mv7M4 --code_state=16 --float_support=FPv4SPD16 -me --

There is the following in the _c_int00_template run time library start-up function which is in the lib/src/boot_cortex_m.c source file in the TI v18.1.1.LTS compiler installation:

   // Initialize the FPU if building for floating point
   #if __ARM_FP 
   volatile uint32_t* cpacr = (volatile uint32_t*)0xE000ED88; 
   *cpacr |= (0xf0 << 16);   
   #endif

Table 2-29 Predefined ARM Macro Names in the ARM Optimizing C/C++ Compiler User's Guide describes the __ARM_FP macro as:

Defined as 6 for --float_support={fpv4spd16 | fpv5spd16}. Defined as 12 for --float_support={vfpv2 | vfpv3 | vfpv3d16}; undefined otherwise.

Therefore, when the --float_support=FPv4SPD16 option is used the run time library start-up code automatically enables the FPU.

0 Charles Tsai over 7 years ago in reply to Chester Gillon

TI__Guru**** 190806 points

Hi Chester,
Thanks for the answer. You are correct that the FPU is enabled in the startup.

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SW-EK-TM4C1294XL: FPU Enable/disable on reset