dsp56800 Freescale Semiconductor, Inc, dsp56800 Datasheet - Page 215

• Manufacturer Part Number: dsp56800
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

8.9
Often, a program spends most of its time in time-critical loops. For the efficient execution of these loops, it
is important to have an adequate number of registers. However, sometimes the registers already contain
data that is not necessary for the critical loop but must not be lost. In this case the DSP56800 architecture
provides a convenient mechanism for freeing up these registers using the software stack. The programmer
pushes any registers containing values not required in the tight loop, freeing up these registers for use.
After completion of the loop, these registers are popped. An example is shown in the following code.
Freescale Semiconductor
Time-Critical DO Loops
SP
Figure 8-1. Example of a DSP56800 Stack Frame
Software Techniques
Second Passed Parameter
Third Passed Parameter
First Passed Parameter
Second Local Variable
Fourth Local Variable
Third Local Variable
Fifth Local Variable
First Local Variable
X Data Memory
Status Register
Return Address
Time-Critical DO Loops
AA0092
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