The MEMORY directive identifies ranges of memory that are physically present in the target system and can be used by a program. Each range has several characteristics:

• Page
• Name
• Starting address
• Length
• Optional set of attributes
• Optional fill specification

The MEMORY directive also allows you to use the GROUP keyword to create logical groups of memory ranges for use with Cyclic Redundancy Checks (CRC). See Section 9.10.2 for how to compute CRCs over memory ranges using the GROUP syntax.

TMS320C28x devices have separate memory spaces (pages) that occupy the same address ranges (overlay). In the default memory map, one space is dedicated to the program area, while a second is dedicated to the data area. (For detailed information about overlaying pages, see Section 9.6.5.2.7.)

In the linker command file, you configure the address spaces separately by using the MEMORY directive's PAGE option. The linker treats each page as a separate memory space. The TMS320C28x supports up to 255 address spaces, but the number of address spaces available depends on the customized configuration of your device (see the TMS320C2xx User's Guide for more information.)

When you use the MEMORY directive, be sure to identify all memory ranges that are available for the program to access at run time. Memory defined by the MEMORY directive is configured; any memory that you do not explicitly account for with MEMORY is unconfigured. The linker does not place any part of a program into unconfigured memory. You can represent nonexistent memory spaces by simply not including an address range in a MEMORY directive statement.

The MEMORY directive is specified in a command file by the word MEMORY (uppercase), followed by a list of memory range specifications enclosed in braces. The MEMORY directive in The MEMORY Directive defines a system that has 4K words of slow external memory at address 0x0000 0C00 in program memory, 32 words of fast external memory at address 0x0000 0060 in data memory, and 512 words of slow external memory at address 0x0000 0200 in data memory. It also demonstrates the use of memory range expressions as well as start/end/size address operators (see Origin and Length as Expressions).

The following example specifies a memory range with the R and W attributes and a fill constant of 0FFFFFFFFh:

MEMORY
{
RFILE (RW) : o = 0x00000020, l = 0x00001000, f = 0xFFFFFFFF
}

You normally use the MEMORY directive in conjunction with the SECTIONS directive to control placement of output sections. For more information about the SECTIONS directive, see Section 9.6.5.

Figure 9-2 illustrates the memory map shown in The MEMORY Directive

Figure 8-2 Memory Map Defined in The MEMORY Directive