Em 22/7/2010 12:51, Matt Rhys-Roberts escreveu:
>> Why don't you pass the port as an argument to the functions?
>> Instead of duplicating a lot of code, just duplicate and select between
>> the code that access the hardware?
>>
>> Or you could do as in desktop systems, OpenSPI takes the port number and
>> returns a handle which must be passed to the other functions or -1 if it
>> fails?
>>
>> This way you could share the SPI ports between threads (if you are using
>> a RTOS). I do it this way in my designs, for SPI, USART, etc.
>>
>>
>> Isaac
>>    =

> Hi Isaac,
>
> Thanks for the reply... Sorry to sound stupid, but you've lost me =

> altogether with "pass the port as an argument to the functions", and =

> "duplicate and select between the code that accesses the hardware" =

> confuses me. Can you suggest an example please?

Example (pseudo-code, not compiled):

static char portisopen[2] =3D { 0 , 0 };

signed char OpenSPI( char port, unsigned char sync_mode, unsigned char
bus_mode, unsigned char smp_phase )
{

    if( port < 1 || port > sizeof portisopen / sizeof portisopen[0] )
        return -1;

    if( portisopen[port-1] !=3D 0 )
        return -1;

    portisopen[port-1] =3D 1;

    if( port =3D=3D 1 )
    {
    // Initialize the hardware of SPI port 1 here.
    }
    else
    {
    // Initialize the hardware of SPI port 2 here.
    }
   =

    return 0;
}

void CloseSPI( char port )
{
    if( port < 1 || port > sizeof portisopen / sizeof portisopen[0] )
        return -1;

    if( portisopen[port-1] =3D=3D 0 )
        return;

    if( port =3D=3D 1 )
    {
    // Stop the hardware of SPI port 1 here.
    }
    else
    {
    // Stop the hardware of SPI port 2 here.
    }

    portisopen[port-1] =3D 0;
}

unsigned char TransceiveSPI( char port, unsigned char data_out )
{
    unsigned char data_in;

    if( port < 1 || port > sizeof portisopen / sizeof portisopen[0] )
        return -1;

    if( portisopen[port-1] =3D=3D 0 )
        return 0;

    if( port =3D=3D 1 )
    {
    // Send data_out and receive_data_in to/from SPI port 1.
    }
    else
    {
    // Send data_out and receive_data_in to/from SPI port 2.
    }

    return data_in;
}


> Referring to http://en.wikipedia.org/wiki/Function_prototype , I =

> understand that prototyping functions before using them helps to make =

> the compiler's job easier and prevents confusing errors.
>
> I'm not multithreading or using a RTOS here, just trying to configure =

> things politely in C so that I can make use of C's more elegant =

> operators when it comes to data manipulation and processing.
>
> NB. I've been using PIC assembly for years, so I'm not familiar with =

> some of the higher-minded C concepts yet!
>
> Best regards,
> Matt.

I understand, your questions were more about of C language techniques
than implementation...
Welcome to the C language world!


Best regards,

Isaac

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