I use LPC2138 and our application is quite time critical so we use interrupts. To enable nested interrupts we use these two macros:

/* Nested Interrupts Entry */
#define NESTED_INTERRUPTS_ENABLE() \
asm volatile ( \
"MRS LR, SPSR \n\t" /* Copy SPSR_irq to LR */ \
"STMFD SP!, {LR} \n\t" /* Save SPSR_irq */ \
"MSR CPSR_c, #0x1F \n\t" /* Enable IRQ (Sys Mode) */ \
"STMFD SP!, {LR} \n\t" /* Save LR */ \
); \
{

/* Nested Interrupts Exit */
#define NESTED_INTERRUPTS_DISABLE() \
} \
asm volatile ( \
"LDMFD SP!, {LR} \n\t" /* Restore LR */ \
"MSR CPSR_c, #0x92 \n\t" /* Disable IRQ (IRQ Mode) */ \
"LDMFD SP!, {LR} \n\t" /* Restore SPSR_irq to LR */ \
"MSR SPSR_cxsf, LR \n\t" /* Copy LR to SPSR_irq */ \
);

While we use IRQ it works fine. But the operating system uses SWI to perform context switch and I don't know how to enable nested interrupts inside SWI ISR. How can I do it to get really fast response on interrupts? I need to enter interrupt service routine within 10us.

Thanks

Change the portENTER_CRITICAL and portEXIT_CRITICAL macros to only disable IRQ, not FIQ, then set your high priroity interrupt to use FIQ. There was something in another thread on this today.