POP

POP Pop a Register from the Software Stack (AGU) POP

Operation

Assembler Syntax

(SP – 8) → De; SP – 8 → SP

POP

De

(SP – 4) → Do; SP – 8 → SP

POP

Do

Description

These operations read the memory address pointed to by the active stack pointer (SP) into an even or odd register (De or Do) 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 the SP of the data being read. 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 POP instructions can appear in an execution set. In both cases, SP is decremented only once by

8.When two POP instructions are grouped together in an execution set, each must be in a different register group.

If the register is a DALU register, bits [39:32] of the destination are sign-extended from bit 31 and the Ln bit is cleared. Hence, in order to restore a full data register, the extension should be popped last.

Extensions of data registers (with the associated Ln bits) are special. Extensions of even and odd registers are read from 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

+

POP De

39

32

16

0

EXTENSION

 

 

De (even)

 

 

 

 

EXTENSION

 

 

Do (odd)

 

 

 

 

 

Restores data register extension pairs, even registers, and loop start registers from the stack. Data register extension pairs are popped the same as even numbered registers.

POP Do

Restores modifier control, odd registers, and loop counter registers from the stack.

SC140 DSP Core Reference Manual

A-347

Page 661
Image 661
Freescale Semiconductor SC140 specifications SP 8 → De SP 8 → SP, SP 4 → Do SP 8 → SP, POP De, POP Do