Can anyone help me understand why subtracting 16 from interrupt address?

jinyoung noh

Prodigy 120 points

Hello everyone,

I am such a beginner. I hope someone can help me understand this question.

I am studying about interrup using given interrupt example.

But there are some codes I cannot understand.

HWREG(NVIC_SW_TRIG) = INT_GPIOC - 16;

I know this code is to trigger GPIOC interrupt on purpose. But I dont know why it is subtracted by 16?

Is INT_GPOIC the address of GPIO interrupt?

It would be really helpful if anyone can give me correct answer.

Thanks,

over 10 years ago

0 Amit Ashara over 10 years ago

TI__Guru**** 244400 points

Hello Jinyoung,

The Exception table for M4 has 0-15 dedicated for internal events. That leaves 16 onwards for any external interrupt. Hence a subtraction of 16 is required to configure the other interrupt sources in the corresponding NVIC registers.

Regards
Amit

0 jinyoung noh over 10 years ago in reply to Amit Ashara

Prodigy 120 points

Thank you so much for your kind expalin. By the way, why is the subtraction of 16 required to configure the other interrupt sources? Cortex will trigger hard fault if there is an attempt to configure the interrupt sources without the subtraction of 16?

0 Amit Ashara over 10 years ago in reply to jinyoung noh

TI__Guru**** 244400 points

Hello Jinyoung,

If not subtracted then the SW will be programming the wrong register bits in the NVIC

Regards
Amit

Arm-based microcontrollers

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Can anyone help me understand why subtracting 16 from interrupt address?