GCBASIC documentation
Compiler Preprocessor Options

Syntax:

    #option ReserveHighProg [words]

This option reserves program memory to be kept free at the top end of memory. This is useful for HEF/SAF or bootloaders.

The option provides a reservation for the memory region that is normally assumed to be available to the compiler for application code storage. In order to avoid any possible conflict (overlapping code and data usage), it is important to reserve the device-specific memory range by using the compiler option (shown above) in the project configuration.

Using #option ReserveHighProg [words] exposes the constant ChipReserveHighProg in the user program.

Defined constants

The compiler has constants that can be used as an alternative to the parameter [words].

The compiler constants are: OPTIBOOT, OPTIBOOTUSB, ARDUINONANO, ARDUINOMEGA2560, or TINYBOOTLOADER.

Where these constants equate to:

    OPTIBOOT        = 1024
    OPTIBOOTUSB     = 2048
    ARDUINONANO     = 1024
    ARDUINOMEGA2560 = 1024
    TINYBOOTLOADER  = 128
    TINYBOOTLOADER128  = 128
    TINYBOOTLOADER125  = 256

Example 1

In the example below, the region 0x1F80 to 0x1FFF (a flash block for a PIC16F1509 microcontroller) has been removed from the default space available for code storage, using the compiler option.

    'Set chip model
    #chip 16F1509

    'Directive
    #option ReserveHighProg 128          ' <<< reserving 128 words of high program memory

Key line: #option ReserveHighProg 128 — reserves the top 128 words of program memory on the 16F1509 so the compiler will never place user code there, leaving that block free for a bootloader or HEF/SAF storage.

Example 2

In the example below, the bootloader area of program memory is protected.

This will ensure the program size does not overwrite the OptiBoot bootloader.

    'Set chip model
    #chip MEGA328P

    'Directive
    #option ReserveHighProg OPTIBOOT

See Also: