Page 220 - The Art of Designing Embedded Systems

A Firmware Standards Manual 207

Make and Proiect Files

Every executable will be generated via a MAKE file, or the equiva-
lent supported by the tool chain selected. The MAKE file includes all of
the information needed to automatically build the entire ROM image. This
includes compiling and assembling source files, linking, locating (if
needed), and whatever else must be done to produce a final ROM image.
An alternative version of the MAKE file may be provided to gener-
ate debug versions of the code. Debug versions may include special diag-
nostic code, or might have a somewhat different format of the binary
image for use with debugging tools.
In integrated development environments (like Visual C++) specify a
PROJECT file that is saved with the source code to configure all MAKE-
like dependencies.
In no case is any tool ever to be invoked by typing in a command, as
invariably command line arguments “accumulate” over the course of a
project . . . only to be quickly forgotten once version 1.0 ships.

Sfartup Code

Most ROM code, especially when a C compiler is used, requires an
initial startup module that sets up the compiler’s runtime package and ini-
tializes certain hardware on the processor itself, including chip selects,
wait states, etc.
Startup code generally comes from the compiler or locator vendor,
and is then modified by the project team to meet specific needs of the pro-
ject. It is invariably compiler- and locator-specific. Therefore, the first
modification made to the startup code is an initial comment that describes
the version numbers of all tools (compiler, assembler, linker, and locator)
used.
Vendor-supplied startup code is notoriously poorly documented. To
avoid creating difficult-to-track problems, never delete a line of code from
the startup module. Simply comment out unneeded lines, being careful to
put a note in that you were responsible for disabling the specific lines. This
will ease re-enabling the code in the future (for example, if you disable the
floating point package initialization, one day it may need to be brought
back in).
Many of the peripherals may be initialized in the startup module. Be
careful when using automatic code generation tools provided by the
processor vendor (tools that automate chip select setup, for example).
Since many processors boot with RAM chip selects disabled, always in-