O.K., I guess I need to review typedefs, unions, and structs.




Hypothetically, would this have been a better way to define OSCCON, in a wo=
rld where it was a good idea to modify Microchip?s device .h files?


__extension__ typedef struct tagOSCCONBITS {
union {
unsigned int VALUE; //Note we can now access OSCCONBITS type OSCCON as an u=
nsigned int via OSCCON.VALUE
struct {
unsigned char HVALUE; //Access to the high
unsigned char LVALUE; //and low bytes of OSCCON
};
struct {
unsigned OSWEN:1;
unsigned LPOSCEN:1;
unsigned :1;
unsigned CF:1;
unsigned :1;
unsigned LOCK:1;
unsigned IOLOCK:1;
unsigned CLKLOCK:1;
unsigned NOSC:3;
unsigned :1;
unsigned COSC:3;
};
struct {
unsigned :8;
unsigned NOSC0:1;
unsigned NOSC1:1;
unsigned NOSC2:1;
unsigned :1;
unsigned COSC0:1;
unsigned COSC1:1;
unsigned COSC2:1;
};
};
} OSCCONBITS;
extern volatile OSCCONBITS OSCCON __attribute__((__sfr__));
=20
=20

One thing that always bugs me about programming languages is when you have =
only one of something, but you have to name a struct/union/class/whatever f=
or it. Now, that can be useful if you have more than one item, or if you wa=
nt to copy it, modify it, and pass it as a parameter, but if there?s genuin=
ely only one of it, and always will be, why do we need to name its arrangem=
ent, instead of simply declaring it?



On 12/29/11, piclist-request@mit.edu wrote:
=20
Message: 32
Date: Thu, 29 Dec 2011 17:20:30 +0100
From: Jan-Erik Soderholm <jan-erik.soderholm@telia.com>
Subject: Re: [PIC] PIC24H Oscillator, OSCCON register
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Message-ID: <4EFC934E.1080704@telia.com>
Content-Type: text/plain; charset=3DISO-8859-1; format=3Dflowed



bladetooth@verizon.net wrote 2011-12-29 16:37:
> But OSCCON is a union, isn?t it? Shouldn?t that mean I can address its
> structured bits? Or am I reading this part of the header file wrong?
>

Yes, you are. OSCCON is an simple "unsigned int".

Then there is another definition of OSCCONBITS that is
a struct (or rather an union of two structs...).

Jan-Erik.


>
> ? extern volatile unsigned int OSCCON __attribute__((__sfr__));
>
> __extension__ typedef struct tagOSCCONBITS { union { struct { unsigned
> OSWEN:1; unsigned LPOSCEN:1; unsigned :1; unsigned CF:1; unsigned :1;
> unsigned LOCK:1; unsigned IOLOCK:1; unsigned CLKLOCK:1; unsigned
> NOSC:3; unsigned :1; unsigned COSC:3; }; struct { unsigned :8; unsigned
> NOSC0:1; unsigned NOSC1:1; unsigned NOSC2:1; unsigned :1; unsigned
> COSC0:1; unsigned COSC1:1; unsigned COSC2:1; }; }; } OSCCONBITS; ?
>
>
>
>
> Ryan Pettigrew
>
> On 12/28/11, piclist-request@mit.edu wrote:
>
>> but can?t seem to do simple things like ?OSCCON.OSWEN =3D true;?
>
> It is always a good idea to look at the appropriate header file.
>
> In most cases, what you want is something like
>
> OSCCONbits.OSWEN =3D 1;
>
> The symbol OSCCON itself refers to the entire register. If it were a
> struct you wouldn' tbe able to say things like
>
> OSCCON =3D 0x1234;
>
> so the struct has a different name. Almost always the register name
> followed by "bits".
>
> But once in a while there are surprises, so don't be shy about studying
> the .h file.
--=20
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