Freescale Semiconductor SC140 Stack Support Instructions, Stack Push/Pop Instructions

Stack Support

5.5.3 Stack Support Instructions

The core provides push and pop instructions that reference the active stack pointer (NSP or ESP). Table 5-11 describes these instructions.

	Table 5-11. Stack Push/Pop Instructions
Instruction	Description
POP	Pre-decrement the stack by eight and restore one 32-bit register
POPN	Same as POP, but using the NSP regardless of the working mode
PUSH	Push a single 32-bit register onto the active stack and increment the pointer by
	eight
PUSHN	Same as PUSH, but using the NSP regardless of the working mode

In addition, the stack can be accessed with move or bit mask instructions that use short and word displacement addressing with the stack pointer as a base pointer. However, these instructions do not change the value of the stack pointer. Generally, the stack pointer points to the next unoccupied location.

While using the pop/push instructions, all SC140 registers are viewed as two separate banks, an even register file bank and an odd register file bank (as shown in Table 5-12).

Table 5-12. Even and Odd Registers

Even Register (De) File	Odd Register (Do) File
D0 D2 D4 D6 D8 D10 D12 D14	D1 D3 D5 D7 D9 D11 D13 D15
D0.e D2.e D4.e D6.e	D1.e D3.e D5.e D7.e
D8.e D10.e D12.e D14.e	D9.e D11.e D13.e D15.e
D0.e:D1.e D2.e:D3.e D4.e:D5.e D6.e:D7.e	R1 R3 R5 R7 R9 R11 R13 R15
D8.e:D9.e D10.e:D11.e D12.e:D13.e D14.e:D15.e	B1 B3 B5 B7
R0 R2 R4 R6 R8 R10 R12 R14	N1 N3 M1 M3
B0 B2 B4 B6	LC0 LC1 LC2 LC3
N0 N2 M0 M2	VBA SR MCTL
SA0 SA1 SA2 SA3

Up to two push instructions are supported in a single execution set. If two push instructions are included in a single execution set, one push instruction must use an even register operand, and the other push instruction must use an odd register operand. A push instruction always pushes one 32-bit register into the stack. Any execution set that includes one or two push instructions increments the stack pointer by eight. In the case of a single push, a single operand is written to the memory while the adjacent memory location remains unchanged.

5-34 SC140 DSP Core Reference Manual