RE: [avr-gcc-list] port access with avr-gdb

[Dave Hylands]

Hi Ned,

I like it!

The really nice thing about this approach is that you should be able to
see the symbolic names of the registers when you disassemble your object
files.

--
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/ 

> -----Original Message-----
> From: address@hidden 
> [mailto:address@hidden On Behalf Of Ned Konz
> Sent: Friday, June 18, 2004 12:41 PM
> To: address@hidden
> Subject: Re: [avr-gcc-list] port access with avr-gdb
> 
> 
> On Sunday 13 June 2004 7:23 am, Dave Hylands wrote:
> > One way to get the registers to show up symbolically, is to 
> create a 
> > structure which has the same layout as the registers. Then you can 
> > access through a null pointer. This would allow you to see the 
> > registers in GDB. They still wouldn't show up I nthe linker map 
> > though.
> >
> > There are ways of making them show up in the linker map too. Just 
> > create an asm file which has each of the registers named. On the C 
> > side you'd have appropriate externs decalred.
> 
> I rather like the way that Microchip's C18 compiler does it...
> 
> extern volatile near unsigned char       PORTA;
> 
> extern volatile near union {
>   struct {
>     unsigned RA0:1;
>     unsigned RA1:1;
>     unsigned RA2:1;
>     unsigned RA3:1;
>     unsigned RA4:1;
>     unsigned RA5:1;
>     unsigned RA6:1;
>   };
>   struct {
>     unsigned AN0:1;
>     unsigned AN1:1;
>     unsigned AN2:1;
>     unsigned AN3:1;
>     unsigned :1;
>     unsigned AN4:1;
>     unsigned OSC2:1;
>   };
>   struct {
>     unsigned :2;
>     unsigned VREFM:1;
>     unsigned VREFP:1;
>     unsigned T0CKI:1;
>     unsigned SS:1;
>     unsigned CLK0:1;
>   };
>   struct {
>     unsigned :5;
>     unsigned LVDIN:1;
>   };
> } PORTAbits;
> 
> 
> So you can just write stuff like:
> 
>       PORTAbits.RA0 = 1;
> 
> or if you want:
> 
>       PORTA |= 1;
> 
> The registers themselves are defined in the processor 
> library, which is 
> compiled from the .asm sources.
> 
> In this case, the corresponding part of the p18f452.h file looks like:
> 
> SFR_UNBANKED0       UDATA_ACS H'F80'  ; segment reference 
> with absolute address
> PORTA               
> PORTAbits           RES 1     ; 0xF80
> 
> This has the added advantage of catching mismatches between 
> bit names and 
> registers.
> 
> It does not tell the compiler that PORTAbits and PORTA are 
> aliases of each 
> other, though since these are all declared as volatile I 
> don't know if that 
> matters much (I suppose it could save a pointer load).
> 
> To avoid that problem you could do this:
> 
> extern volatile near union {
>   struct {
>     unsigned RA0:1;
>     unsigned RA1:1;
>     unsigned RA2:1;
>     unsigned RA3:1;
>     unsigned RA4:1;
>     unsigned RA5:1;
>     unsigned RA6:1;
>   };
>   struct {
>     unsigned AN0:1;
>     unsigned AN1:1;
>     unsigned AN2:1;
>     unsigned AN3:1;
>     unsigned :1;
>     unsigned AN4:1;
>     unsigned OSC2:1;
>   };
>   unsigned char bits;
> } PORTAbits;
> 
> #define PORTA PORTAbits.bits
> 
> This also allows re-use between processor families if you're 
> clever; each 
> family of functions (say PORTA and its usual pin definitions) 
> could be in a 
> separate header file, with only the things like the pin 
> overloading (here, 
> for instance, RA0 and AN0 are on the same pin) being 
> processor-specific.
> 
> I wasn't able to see Larry's suggestion, as it got stripped.
> 
> -- 
> Ned Konz
> http://bike-nomad.com
> GPG key ID: BEEA7EFE
> 
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