Mainly out of idle curiosity, I looked up how FreeRTOS handles context switching. They define two macros to handle this as follows. Perhaps this will offer some clues about the syntax. Evidently, the stack pointer is known as "r1".
From MSP430 CPU:
The processor contains 16 16-bit registers, of which 4 are dedicated to special purposes: R0 is the program counter, R1 is the stack pointer, R2 is the status register, and R3 is a special register called the constant generator, providing access to 6 commonly used constant values without requiring an additional operand. R3 always reads as 0 and writes to it are ignored. R4 through R15 are available for general use.
/* * Macro to save a task context to the task stack. This simply pushes all the * general purpose msp430 registers onto the stack, followed by the * usCriticalNesting value used by the task. Finally the resultant stack * pointer value is saved into the task control block so it can be retrieved * the next time the task executes. */ #define portSAVE_CONTEXT() \ asm volatile ( "push r4 \n\t" \ "push r5 \n\t" \ "push r6 \n\t" \ "push r7 \n\t" \ "push r8 \n\t" \ "push r9 \n\t" \ "push r10 \n\t" \ "push r11 \n\t" \ "push r12 \n\t" \ "push r13 \n\t" \ "push r14 \n\t" \ "push r15 \n\t" \ "mov.w usCriticalNesting, r14 \n\t" \ "push r14 \n\t" \ "mov.w pxCurrentTCB, r12 \n\t" \ "mov.w r1, @r12 \n\t" \ ); /* * Macro to restore a task context from the task stack. This is effectively * the reverse of portSAVE_CONTEXT(). First the stack pointer value is * loaded from the task control block. Next the value for usCriticalNesting * used by the task is retrieved from the stack - followed by the value of all * the general purpose msp430 registers. * * The bic instruction ensures there are no low power bits set in the status * register that is about to be popped from the stack. */ #define portRESTORE_CONTEXT() \ asm volatile ( "mov.w pxCurrentTCB, r12 \n\t" \ "mov.w @r12, r1 \n\t" \ "pop r15 \n\t" \ "mov.w r15, usCriticalNesting \n\t" \ "pop r15 \n\t" \ "pop r14 \n\t" \ "pop r13 \n\t" \ "pop r12 \n\t" \ "pop r11 \n\t" \ "pop r10 \n\t" \ "pop r9 \n\t" \ "pop r8 \n\t" \ "pop r7 \n\t" \ "pop r6 \n\t" \ "pop r5 \n\t" \ "pop r4 \n\t" \ "bic #(0xf0),0(r1) \n\t" \ "reti \n\t" \ );
