Understanding Memory Widths
10-10
10.4.1 Target Width
Target width is the unit size (in bits) of raw data fields in the COFF file. This
corresponds to the size of an opcode on the target processor. The width is fixed
for each target and cannot be changed. The TMS320C54x targets have a
width of 16 bits.
10.4.2 Data Width
Data width is the logical width (in bits) of the data words stored in a particular
section of a COFF file. Usually, the logical data width is the same as the target
width. The data width is fixed at 16 bits for the TMS320C54x and cannot be
changed.
10.4.3 Memory Width
Memory width is the physical width (in bits) of the memory system. Usually, the
memory system is physically the same width as the target processor width: a
16-bit processor has a 16-bit memory architecture. However, some applica-
tions require target words to be broken up into multiple, consecutive, narrower
memory words. Moreover, with certain processors like the ’C54x, the memory
width can be narrower than the target width.
The hex conversion utility defaults memory width to the target width (in this
case, 16 bits).
You can change the memory width by:
-
Using the –memwidth option. This changes the memory width value for
the entire file.
-
Setting the memwidth parameter of the ROMS directive. This changes
the memory width value for the address range specified in the ROMS
directive and overrides the –memwidth option for that range. See Section
10.5,
The ROMS Directive, on page 10-16.
For both methods, use a
value that is a power of 2 greater than or equal to 8.
You should change the memory width default value of 16 only in exceptional
situations: for example, when you need to break single target words into
consecutive, narrower memory words. Situations in which memory words are
narrower than target words are most common when you use on-chip boot
loaders — several of which support booting from narrower memory. For exam-
ple, a 16-bit TMS320C54x can be booted from 8-bit memory or an 8-bit serial
port, with each 16-bit value occupying two memory locations (this would be
specified as –memwidth 8).
Summary of Contents for TMS320C54x
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