Rabbit 2000, Designers Handbook

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Designer’s Handbook 19
5.3
Internally defined macros
Some
macros used in the BIOS are defined internally by Dynamic C before the BIOS is
compiled.
They are defined using tests done in the bootstrap loading, or by reading vari-
ables
set in the GUI. These are:
_FLASH_, _RAM_
- Used for conditional compilation of the BIOS to distinguish
between
compiling to RAM and compiling to flash. The Options | Compile dialog controls
these.
_RAM_SIZE_, _FLASH_SIZE_
- Used to set the MMU registers and code and data
sizes
available to the compiler. The values given by these macros represent the number of
0x1000
blocks of memory available.
_BOARD_TYPE_
-
This is read from the System ID block or defaulted to 0x100 (the
BL1810
JackRabbit board) if no System ID block is present. This can be used for condi-
tional
compilation based on board type.
5.4
Modifying the BIOS
The
BIOS can be modified to be more specific concerning the user’s configuration. This
can
be done one step at a time, making it easy to detect any problems. The source code for
the
Universal BIOS is in
BIOS\RABBITBIOS.C.
Dynamic C uses this source code for
the
BIOS by default, but the user can specify another BIOS for Dynamic C to use in
Options
| Compiler
There
are several macros at the top of
RABBITBIOS.C
that users may want to modify for
boards
they design or for special situations involving off-the-shelf, Rabbit based boards.
USE115KBAUD
The
default value, 1, specifies that Dynamic C will communicate at 115,200 baud with the
target.
If this macro is set to zero, Dynamic C will communicate at 57,600 baud. The
lower
baud rate might be needed on some PC’s that can’t handle 115,200 baud. If this is
changed
to zero, the baud rate in Dynamic C Options | Serial should be changed to 57,600
also.
CLOCK_DOUBLED
The
default value of 1 causes the clock speed to be doubled if the crystal speed is less than
or
equal to 12.9 MHz. Setting this to zero means the clock speed will not be doubled.
ENABLECLONING
The
default value of 0 disables cloning. Setting this to 1 enables cloning and increases the
code
size of the BIOS somewhat.