Motorola MSC8101 ADS User's Guide download pdf (Page 72)

3-2 MSC8101 User’s Guide

Optimizing Memory on the SC140 Core

■ The SC140 core does not support accesses to a non-existent memory location. If

required, the memory subsystem detects these occurrences and generates

non-maskable interrupts (NMIs) to the SC140 core.

3.2 Partitioning Memory

The SC140 core is flexible in its support for various memory structures, including

different division into submemories. The example in Figure 3-1 presents a general

structure that partitions the memory as follows:

■ The memory is made up of a number of 32 KB groups.

■ Each group consists of eight 4 KB modules.

■ Each module includes 128 rows.

Addresses are interleaved over the modules within a group, in row boundaries. This

organization enables consecutive addressing across more than one module in a group.

3.3 Allocating Memory

The compiler allocates program memory and data RAM. By default, the program memory

is allocated to the subroutines sequentially. In the data memory, a sophisticated algorithm

efficiently allocates the various arrays and variables. For each variable or array, a time

period analysis is performed in which the living time of the array or variable is examined,

and the option to share other variables on the same physical memory locations is tested. If

there is no overlap in the living times of two variables, they can share the same memory

location. The algorithm generally finds the most efficient way to allocate the variables.

Therefore, it is recommended that you allow the compiler to allocate the data RAM.

However, for flexibility, the option to allocate memory manually still exists. In

memory-critical applications, a more optimized allocation may be achieved by manual

allocation.

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Motorola MSC8101 ADS User's Guide Page 72