arm - 有谁知道如何启用ARM FIQ？

Question

有谁知道如何启用ARM FIQ？

Answer 1

除了在管理员模式下启用或禁用 IRQ/FIQ 之外，您无需在 ARM 上进行任何特殊设置即可使用它，除非系统(运行 ARM 芯片的系统)在硬件中禁用了它(根据您的评论，情况并非如此，因为您看到 FIQ 输入引脚驱动正确)。

For those unaware of the acronyms, FIQ is simply the last interrupt vector in the list which means it's not limited to a branch instruction as the other interrupts are. That means it can execute faster than the other IRQ handlers.

Normal IRQs are limited to a branch instruction since they have to ensure their code fits into a single word. FIQ, because it won't overwrite any other IRQ vectors, can just run the code directly without a branch instruction (hence the "fast").

The FIQ input line is just a way for external elements to kick the ARM chip into FIQ mode and start executing the correct exception. There's nothing on the ARM itself which prevents that from happening except the CPSR.

在管理员模式下启用 FIQ:

MRS r1, cpsr         ; get the cpsr.
BIC r1, r1, #0x40    ; enable FIQ (ORR to disable).
MSR cpsr_c, r1       ; copy it back, control field bit update.

可以对普通 IRQ 执行类似的操作，但使用 #0x80 而不是 #0x40。