The maximum number of interrupt sources handled by the nested vectored interrupt

Question

The maximum number of interrupt sources handled by the nested vectored interrupt controller (NVIC) in a Microcontroller STM32F407 is a. 16. b. 23. c. 82. The vector table of an ARM Cortex-M4 processor a. always locates in the memory beginning at the address 0 times 0000 0000. b. can be relocated in any memory location by the linker. c. locates in data memory beginning at 0 times 2000 0000. The interrupt latency of an ARM Cortex-M4 processor a. is always equal to 12 system cycles. b. is not less than 12 system cycles. c. is not more than 12 system cycles. Assume that the clock of SysTick timer is 168 MHz. To configure the timer to generate SysTick interrupt every 1 ms, the number to be written reload value register is a. 168 b. 168 times 10^3 c. 168 times 10^6

Explanation / Answer

Advanced Microprocessors

5. b

Any STM32F4 device has 23 external interrupt or event sources. They are split into 2 sections. First, interrupt section is for external pins (P0 to P15) on each port, and another section is for other events like RTC interrupt, Ethernet interrupts USB interrupt and so on.

6.a

On reset, the vector table is located at address 0x00000000.

7. b

The latency count for Cortex-M4 is listed as 12 and is the exact number of cycles from the assertion of the interrupt request up to the cycle where the first instruction of the interrupt handler is ready to be expected, in a system with zero wait state memory systems.The memory system has zero wait state means resources are not being used by other bus masters.Additional software wrapper code is needed for interrupt handlers to handle the stacking of registers, So this is the minimum cycle requires, it may take more.

8.b

The System clock has a frequency of 168MHz. Time period of System clock=(1/168e6)sec

We have to generate interrupt every 1ms.

So, the number of System clock cycles in 1ms = (1ms / Time period of system clock) = 1e-3* 168e6=168e3

This is the number to be written in reload value register.

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