GCBASIC documentation
Tricks and Tips

This is a collation of tricks and tips that may be useful to you.

RAM, variables and resets

Reverting the FOR-NEXT loop to the Legacy FOR-NEXT method

Change the compilers behaviour when the compiler states a capability is not available

Create a minimal ASM source with no config and/or initsys

PPS microconrollers and multiple USARTs

TIP: RAM, variables and resets

When you define a variable it will be mapped to a RAM location.   As you develop your solution your should always do the following to ensure the variable are initialised correctly.  

A variable will not show up in the ASM source code unless it is used somewhere in code.    Adding Variable = 0 will assure that the variable is initialised and will show up in the ASM.   This is very useful for troubleshooting.   This is essential when debugging ASM to look at variables that are defined using "EQU".   If you do not initialise or use the variable then the variable will not be shown in the EQU list of variables.   So, initialise all your variables.

A soft reset when debugging/testing/programming will not reset the RAM to a known state. This is essential when debugging ASM to look at variables that are defined using "EQU".   A soft reset does not change the contents of RAM.   Where a hard reset reverts ram back to an undefined /random state!   So, a power cycle is good practice.  

TRICK: Reverting the FOR-NEXT loop to the Legacy FOR-NEXT method ?

Why do this? To reduce the PROGMEM size.   But, you must assure yourself that the loop variable cannot overflow as the legacy FOR-NEXT does not prevent an overflow of the loop variable.

Some background.   In 2021 the GCBASIC compiler was updated to improve the operation of the FOR-NEXT loop.   The improvement did increase the size of the ASM generated.   The legacy FOR-NEXT loop had some major issues that included never ending loops, incorrect end loop and unexpected operations.   This was all caused by the compiler, not the user, and in 2021 the compiler was updated to resolve these issues.  

However, there is a risk that the new FOR-NEXT method causes 1) larger ASM that will not fit in small microcontrollers or 2) the new code does not operate as expected.   In either case you can disable the new FOR-NEXT method by adding a constant as shown below.   Adding this constant will revert the FOR-NEXT loop asm generated to the legacy method.  

    #DEFINE USELEGACYFORNEXT

TRICK: How to change the compilers behaviour when the compiler states a capability is not available when I know it is ?

The compiler is issuing an error message that a EEPROM, HEF, SAF, PWM16 or hardware USART is not available…​ but, it is.  

This is caused by the microcontroller DAT file.   The microcontroller DAT file is missing key information that informs the compiler that a specific capability is available.   This information was added to prevent silent failures where you could use a capability when it is not available.  

The compiler thinks your microcontroller does not have the selected capability.    Simply use the table below to resolve.   Adding the constant defined to your source program.  

Then, let us know via the Forum so we can correct the source microcontroller DAT file.

TRICK: How do I create a minimal ASM source with no config and/or initsys?

Very easy.   Simple add two #OPTION statements.  

#OPTION UserCodeOnly ENTERBOOTLOADER:   This will instruct the compiler to NOT call the INITSYS() method.   And, to jump to a label.   The label is mandated.  The label specified will be included in the ASM generated.

#OPTION NoConfig  This will instruct the compiler to NOT add the microcontroller specific config statements.

Example:

    #chip 16f877a, 4
    #OPTION Explicit

    #OPTION UserCodeOnly ENTERBOOTLOADER:
    #OPTION NoConfig

    ENTERBOOTLOADER:

The example above yields the following asm.   Comment lines have been removed for clarity.

     LIST p=16F877A, r=DEC
    #include <P16F877A.inc>

    ;Vectors
      ORG 0
      pagesel ENTERBOOTLOADER
      goto  ENTERBOOTLOADER

    ;ORG 5


    ENTERBOOTLOADER

    ;ORG 2048
    ;ORG 4096
    ;ORG 6144

     END

TIP: PPS and multiple USARTs

You can set up multiple pins to simultaneously operate as a peripheral output on microcontrollers with Peripheral Pin Select (PPS).

PPS microcontrollers can set up to simultaneously output specific modules.   The example below shows the method to output two TX ports.   Hardware Serial (TX1) data will now be output on both B.6 and C.6

    Sub InitPPS
            'Module: UART pin directions
            Dir PORTC.6 Out    ' Make TX1 pin an output
            Dir PORTB.6 Out    ' Make TX1 pin an output
            'Module: UART1 to two ports
            RC6PPS = 0x0020    'TX1 > RC6
            RB6PPS = 0x0020    'TX1 > RB6

    End Sub