Computers as Components, 2nd Edition

6.2 Preemptive Real-Time Operating Systems 315

( void ) ulCriticalNesting;

( void ) pxCurrentTCB;

}

Here is the assembly language code for portRESTORE_CONTEXT:

LDR R0, =pxCurrentTCB

LDR R0, [R0]

LDR LR, [R0]

/* The critical nesting depth is the first item on the

stack. */

/* Load it into the ulCriticalNesting variable. */

LDR R0, =ulCriticalNesting

LDMFD LR!, {R1}

STR R1, [R0]

/* Get the SPSR from the stack. */

LDMFD LR!, {R0}

MSR SPSR, R0

/* Restore all system mode registers for the task. */

LDMFD LR, {R0-R14}ˆ

NOP

/* Restore the return address. */

LDR LR, [LR, #+60]

/* And return - correcting the offset in the LR to obtain

the */

/* correct address. */

SUBS PC,