From: Bob Blick <bobblick@outlook.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Thu, 30 Jul 2020 17:43:02 -0700
Subject: Re: [PIC] Simple GCC question
Thread-Topic: [PIC] Simple GCC question
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Hi Mike,

That was simple, and not only did it compile, but my LCD display still work=
s.

Thank you so much and thanks for all the other answers!

Bob

________________________________________
From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Mike=20
Sent: Thursday, July 30, 2020 2:36 PM
To: piclist@mit.edu
Subject: Re: [PIC] Simple GCC question

I strongly suspect the non-constant value GCC is complaining about is
the return value from Lcd_create().  Since the lcd structure is being
initialased via a function call you cannot do this outside of a
function.  You can however define an instance of the lcd struct outside
of a function, and then initialise it later.

Something like this should work:

main.c

#include <lcd.h>

/* These can be initialised outside a function since the initialisers are c=
onstant */
Lcd_PortType ports[] =3D {LCD_D4_GPIO_Port, LCD_D5_GPIO_Port, LCD_D6_GPIO_P=
ort, LCD_D7_GPIO_Port};
Lcd_PinType pins[] =3D {LCD_D4_Pin, LCD_D5_Pin, LCD_D6_Pin, LCD_D7_Pin};
/* You can only define an instance of Lcd_HandleTypeDef here, since the ini=
tialiser is a function */
Lcd_HandleTypeDef lcd;

void main(void)
{
   /* Initialise the lcd here */
   lcd =3D Lcd_create(ports, pins, LCD_RS_GPIO_Port, LCD_RS_Pin, LCD_EN_GPI=
O_Port, LCD_EN_Pin, LCD_4_BIT_MODE);

   /* Other stuff */
   for(;;);
}


mymodule.c

#include <lcd.h>

/* Declare the lcd struct defined in main  */
extern Lcd_HandleTypeDef lcd;

void myfunction(void)
{
   Lcd_clear(&lcd);
}


This is the simplest way I could show this, but using global variables
isn't typically the nicest way to do things.

Regards

Mike


On 30/07/2020 17:26, Bob Blick wrote:
> I'm using a nice little HD44780 LCD library in an STM32 project, it works=
 great but I'm stuck with a variable scope problem that I can only seem to =
make worse because GCC is a bit stricter than I want it to be at this point=
.. Sorry if the code example doesn't wordwrap properly.
>
> If, somewhere in main() I create an instance of the LCD like this:
>    Lcd_PortType ports[] =3D {LCD_D4_GPIO_Port, LCD_D5_GPIO_Port, LCD_D6_G=
PIO_Port, LCD_D7_GPIO_Port};
>    Lcd_PinType pins[] =3D {LCD_D4_Pin, LCD_D5_Pin, LCD_D6_Pin, LCD_D7_Pin=
};
>    Lcd_HandleTypeDef lcd =3D Lcd_create(ports, pins, LCD_RS_GPIO_Port, LC=
D_RS_Pin, LCD_EN_GPIO_Port, LCD_EN_Pin, LCD_4_BIT_MODE);
>
> then I can use it like this:
>    Lcd_cursor(&lcd, 1,6);
>
> but of course I can't do that from within another function since "lcd" on=
ly exists in main()
>
> If I try to make it all global by creating lcd outside of main(), GCC doe=
sn't like that because initializer elements must be constants and it doesn'=
t consider "ports" and "pins" to be constants.
>
> Not being a real C programmer this has stopped me in my tracks. If I was =
stuck on a deserted island I would use this library as a basis for somethin=
g with ports and pins hardcoded, but I'm hoping a real expert would give me=
 some gentle help, which will certainly educate me about doing things the c=
orrect way and also get me past this little hurdle.
>
> Thanks, Bob

--

--=20
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