Texas Instruments TMS320C80, User Manual

Page: 36 / 64

Technique #1: Using Only Common RAM
2-6 TMS320C80 to TMS320C82 Software Compatibility User’s Guide
2.3 Technique #1: Using Only Common RAM
A particularly simple technique for achieving compatibility is to
use only the portions of the on-chip RAM that are common to the
’C80 and ’C82.
The ’C80’s memory map for the local RAMs belonging to the MP,
PP0, and PP1 is a subset of the ’C82’s memory map. All of the
valid local RAM addresses for the ’C80’s MP, PP0, and PP1 cor-
respond to populated local RAM addresses in the ’C82. There-
fore, ’C80 code written to use on-chip RAM belonging to the MP,
PP0, and PP1 should run on the ’C82 without modification.
2.3.1 Advantages of Technique #1
This technique offers three main advantages:
-
It is simple to implement.
-
Performance is nearly identical on the ’C80 and ’C82.
-
All of the RAM available to the ’C80’s MP, PP0, and PP1 can
be used.
2.3.2 Disadvantages of Technique #1
This technique has two main disadvantages:
-
All of the RAM available to the ’C82 cannot be used.
-
Contention may result in the ’C82 since the space occupied
by two RAMs (data RAM 0 and data RAM 1) in the ’C80 is oc-
cupied by one RAM (data RAM 0) in the ’C82.
2.3.3 Implementing Technique #1
In order to implement this technique, place three restrictions
upon your program:
-
Use only RAM that is common to both the ’C80 and ’C82.
-
Do not require your program to use RAM belonging to PP2
and PP3 on the ’C80, since the ’C82 doesn’t have these PPs.
-
Do not use absolute addresses to access the PP stacks since
the PP stacks have different locations in the ’C80 and ’C82.