(15 points) Suppose register į (į s 12) is initialized to have a value of 2*į (e.g. r0 = 0, r1= 2, r2 = 4, r3 = 6, ..., r12 = 24). Assume the main stack (MSP) is used. The program status register (PSR) = 0x00000020, PC = 0x08000020, and LR = 0x20008020, when the interrupt occurs. a. Show the stack content immediately before the PUSH instruction is executed. Suppose the stack pointer SP, i.e. MSP in this case, was 0x20000600 immediately before the system timer interrupt occurs. (7 points) SysTick Handler PROC PUSH {r7, r5) ADD ro, ro, #1 ADD r1, r1, #1 ADD r2, r2, #1 ADD r3, r3, #1 ADD r4, r4, #1 ADD r5, r5, #1 ADD r6, r6, #1 ADD r7, r7, #1 ADD r11, r11, #1 ADD r12 r12, #1 POP {r7, r5) BX LR ENDP