[Solved] You have a FreeRTOS system on a Cortex-M7 with 5 priority bit... What should configMAX_SYSCALL_INTERRUPT_PRIORITY be set to?Note: Priority values are shifted left to fill the 8-bit priority register. | FreeRTOS

FreeRTOS - Interrupt Management

You have a FreeRTOS system on a Cortex-M7 with 5 priority bits. You want to allow interrupts with priority 16 and lower (numerically higher) to call FreeRTOS API safely. What should configMAX_SYSCALL_INTERRUPT_PRIORITY be set to?

Note: Priority values are shifted left to fill the 8-bit priority register.

A0x40

B0x10

C0x20

D0x80

Step-by-Step Solution

Solution:

Step 1: Calculate shifted priority value
With 5 priority bits, priorities are left-shifted by (8 - 5) = 3 bits. Priority 16 decimal = 0x10 hex. Shift left by 3 bits: 0x10 << 3 = 0x80.
Step 2: Match shifted value to options
0x80 matches 0x80, confirming the correct shifted priority value.
Final Answer:
0x80 -> Option D
Quick Check:
Priority 16 << 3 bits = 0x80 [OK]

Quick Trick: Shift priority left by (8 - priority bits) to get config value [OK]

Common Mistakes:

Not shifting priority bits correctly
Confusing decimal and hex values
Choosing unshifted priority values

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More FreeRTOS Quizzes

What should configMAX_SYSCALL_INTERRUPT_PRIORITY be set to?Note: Priority values are shifted left to fill the 8-bit priority register.

Step 1: Calculate shifted priority value

Step 2: Match shifted value to options

Final Answer:

Quick Check:

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