#Option StartupMethodsDisabled

Syntax:

    #option StartupMethodsDisabled

Explanation:

#option StartupMethodsDisabled stops GCBASIC calling the startup routines at the start of the program. These are InitSys (the chip setup: ports digital, the oscillator, the A/D off and so on) and the routines that libraries add with #startup, for example InitRandom, HI2CInit, InitGLCD or the USB library’s startup routine.

Use it when the program must decide what happens first, and when. For example:

  • a board where a pin must be set before anything else runs: InitSys would clear a port and switch a supply on at the wrong moment;
  • a program loaded by a bootloader that has already set the chip up;
  • a program that starts a display or a USB connection only after its own power-up sequence.

The rest of the program is compiled as usual: the stack, the interrupt vectors and the main program are not changed (compare #option UserCodeOnly, which also leaves out the start-up code before the main program).

What the option does:

  • The startup calls are written to the assembler file as comments, under the heading ;! Prepocessor Disabled Calls, so the program shows which routines it would have called. For example: 

    ;Call initialisation routines
;! Prepocessor Disabled Calls
;!  call INITSYS
;!  call INITRANDOM
  • A startup routine is compiled only when the program calls it itself. A routine that is not called is not in the program at all, so it uses no program memory.
  • The program must do itself whatever it needs from the routines that are not called: set the ports, the analogue pins and the oscillator as InitSys would, call InitGLCD before drawing, call Randomize before Random, start the hardware I2C, and so on. Any startup routine can be called by name, for example InitSys or InitGLCD.
  • RAM is not cleared at the start: set every variable before it is used.

Example:

The PIC18F Starter Kit 1: the application power (APP_POWER, RC0) must stay off until its soft start, so the program does not call InitSys (which would clear PORTC) and starts the display itself. 

    #chip 18F46J50, 48
    #option StartupMethodsDisabled      ' no InitSys: it would switch APP_VDD on without a soft start

    #include <PIC18StarterKit1.h>         ' APP_POWER, SD_CS, ACCEL_CS, MENU_BUTTON, AppPowerOn
    #include <glcd.h>
    #define GLCD_TYPE GLCD_TYPE_SH1101A
    ' ... the GLCD bus settings ...

    ' what InitSys would have done, minus the PORTC clear
    INTCON = 0
    TBLPTRU = 0                         ' for ReadTable
    APP_POWER = 1 : Dir APP_POWER Out   ' keep APP_VDD off until AppPowerOn
    SD_CS = 1 : Dir SD_CS Out
    ACCEL_CS = 1 : Dir ACCEL_CS Out
    Dir MENU_BUTTON In

    AppPowerOn                          ' APP_VDD on with the soft start
    InitGLCD                            ' the display's startup routine, called by the program
    GLCDCLS

InitGLCD is compiled because the program calls it; InitSys and the other startup routines are not.

Notes:

  • Build 1662 and later: a startup routine that the program does not call is not compiled. Earlier builds compiled the routines although nothing called them (for example 66 bytes on a PIC18F46J50).
  • Build 1661 and later: InitSys is no longer requested with this option.
  • The option works for PIC and AVR.

See also #startup, #Option UserCodeOnly, #Option Bootloader

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