Hi Andrew,
On Fri, 2007-07-20 at 08:55 +0200, Andrew Victor wrote:
> > Just an example from sound/soc/at91/at91-ssc.c
> >
> > rcmr = (( ssc_p->rcmr_period << 24) & AT91_SSC_PERIOD)
> > | (( 1 << 16) & AT91_SSC_STTDLY)
> > | (( AT91_SSC_START_FALLING_RF ) & AT91_SSC_START)
> > | (( AT91_SSC_CK_RISING ) & AT91_SSC_CKI)
> > | (( AT91_SSC_CKO_NONE ) & AT91_SSC_CKO)
> > | (( AT91_SSC_CKS_DIV ) & AT91_SSC_CKS);
>
> Well, I didn't write the above, so it's more complex than it needs to
> be.
>
> For bitfields where the user can input any value we would usually add
> to
> the header:
> #define AT91_SSC_STTDLY_(x) ((x) << 16)
> #define AT91_SSC_PERIOD_(x) ((x) << 24)
>
> Then it can simply be re-written as:
>
> rcmr = AT91_SSC_PERIOD(ssc_p->rcmr_period)
> | AT91_SSC_STTDLY(1)
> | AT91_SSC_START_FALLING_RF
> | AT91_SSC_CK_RISING
> | AT91_SSC_CKO_NONE
> | AT91_SSC_CKS_DIV;
This is more sane and readable.
> > Would with the header style for atmel-ssc be:
> >
> > rcmr = SSC_BF(RCMR_PERIOD, ssc_p->rcmr_period)
> > | SSC_BF(RCMR_STTDLY, 1)
> > | SSC_BF(RCMR_START, 4)
> > | SSC_BF(RCMR_CKI, 1)
> > | SSC_BF(RCMR_CKO, 0)
> > | SSC_BF(RCMR_CKS, 0);
> >
> > I find the latter more readable and compact, the user also does not
> need
> > to know the offset of the different bit-fields.
>
> But the user does then constantly have to refer to the datasheet to
> determine what CKI = 1 or CKS = 0 means.
As I said two lines furter down, I think these defines are nice. Will
adding bit-field descriptors make the SSC driver more usable by the AT91
people?
I guess there is also the possibility to include the ARM headers for
that architecture and use the definitions in the header file for AVR32.
--
With kind regards,
Hans-Christian Egtvedt, siv.ing. (M.Sc.)
Applications Engineer - AVR32 System Solutions - Atmel Norway
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