Embedded Systems Design, 2nd Edition

Memory systems 125

contents of the ROM is copied into the RAM area where it

can be executed. This part is common to both implementa-

tions.

• With a hardware assisted implementation, the address

decode logic is used to switch the address decode to select

the RAM instead of the ROM. As a result, any access to the

ROM will be automatically switched to the RAM and will

execute faster and without any change in the software as the

addressing has not changed. This also provides an option to

execute the code out of ROM or RAM and this can be used

to isolate problems when executing out of RAM. If there are

software-based timing routines in the ROM code, then this ...