hello , How to enable / disable a global interrupt on cortex M7

Not sure what you mean by global interrupt. For peripheral interrupts, if you are using device driver library with CMSIS-CORE support, you can use:

NVIC_EnableIRQ(IRQn_Type IRQn);

  and

NVIC_DisableIRQ(IRQn_Type IRQn);

Details of NVIC functions are listed in:

https://www.keil.com/pack/doc/CMSIS/Core/html/group__NVIC__gr.html

If you want to disable all interrupts (i.e. setting the PRIMASK register), you can use :

__disable_irq(); // Set PRIMASK

__enable_irq(); // Clear PRIMASK

See the following page for accessing processor's special registers:

https://www.keil.com/pack/doc/CMSIS/Core/html/group__Core__Register__gr.html