Freescale Semiconductor SC140 De → SP SP + 8 → SP, Do → SP + 4 SP + 8 → SP, Push De, Push Do

PUSH

PUSH Push a Register onto the Software Stack (AGU) PUSH

Operation	Assembler Syntax
De → (SP); SP + 8 → SP	PUSH	De
Do → (SP + 4); SP + 8 → SP	PUSH	Do

Description

These operations move an even or odd register (De or Do) to the active stack in memory and adjust SP. All memory accesses are 32-bit long words. The registers are divided into two groups (even and odd) which determines the memory offset relative to SP of the data being written. It is important to pop registers in the same register grouping by which they were pushed. For example, after the sequence "push d1" and "pop d3," d3 will hold the data originally in d1. However, "push d0" and "pop d1" will not do the same because d0 and d1 are not in the same register group.

One or two PUSH instructions can appear in an execution set. In both cases, SP is incremented only once by 8. When two PUSH instructions are grouped together in an execution set, each must be in a different register group.

Extensions of data registers (with the associated Ln bits) are special. Extensions of even and odd registers are written to bits [8:0] and [24:16] of the long data word, respectively, both for single register and register pair operations (see the figure below).

Note: For proper data register restoration, extensions that were pushed as a pair should be popped as a pair. Extensions pushed as single registers should be popped as single registers.

31	24	16	8		0
0		Do	0	De		MEMORY LONG WORD

La	+
Lb	+

PUSH De

39	32	16	0
EXTENSION				De (even)
EXTENSION				Do (odd)

Pushes data register extension pairs, even registers, and loop start registers onto the current stack. Data register extension pairs are pushed the same as even numbered registers.

PUSH Do

Pushes modifier control, odd registers, and loop counter registers onto the current stack.

SC140 DSP Core Reference Manual A-353