Freescale Semiconductor SC140 DSP Core, Reference Manual

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A-356 SC140 DSP Core Reference Manual
PUSHN
PUSHN
Push a Register onto the Software Stack
PUSHN
Using the Normal Stack Pointer (AGU)
Description
These operations move an even or odd register (De or Do) to the normal stack in memory and adjusts the
NSP, regardless of the state of the exception (EXP) bit. 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 NSP
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 "pushn d1" and "popn d3," d3 will hold the data originally in d1.
However, "pushn d0" and "popn d1" will not do the same because d0 and d1 are not in the same register
group.
One or two PUSHN instructions can appear in an execution set. In both cases, NSP is incremented only
once by 8. When two PUSHN 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
Operation Assembler Syntax
De
→
(NSP); NSP + 8
→ Ν
SP
PUSHN De
Do
→
(NSP + 4); NSP + 8
→ Ν
SP
PUSHN Do
PUSHN De
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.
PUSHN Do
Pushes modifier control, odd registers, and loop counter registers onto the current stack.
39 0 16 32
0 16 31 24 8
0 0
EXTENSION
EXTENSION
De (even)
Do (odd)
La +
Lb +
MEMORY LONG WORD
Do De