Re: [linuxsh-dev] Dreamcast RTC

[M. R. B. <ma...@uw...>]

On Thu, 7 Dec 2000, Philipp Rumpf wrote:

> On Wed, Dec 06, 2000 at 07:36:39PM -0600, M. R. Brown wrote:
> > On Thu, 7 Dec 2000, Rene Malmgren wrote:
> > > These funktions can be switched in att compile time or dynamicly at runtime.
> > > Then we simply write an rtc_gen.c and a rtc_dc.c, or perhaps even an
> > > rtc_sh3_gen.c, rtc_sh4_gen.c and an rtc_sh4_dc.c. Then we make all the other
> > > functions that use ther RTC access it through these two funktions. The
> > > get_timer_freq for instance. No modification has to be made to the generic
> > > code at all. You just simply chose the type of timer you want. We should
> > > consider doing the same thing to the timers aswell.
> 
> > Rene, what you just described is *exactly* what Phillip is planning to do.
> > He's moving generic SH4 RTC code into rtc.c so the generic SH4 target (and
> > any other machine that uses the SH4's builtin RTC) can use it.  Then he's
> > adding get_timer_frequency, get_rtc_time, and set_rtc_time to the machine
> 
> that's the main difference between Rene's proposal and mine:  I think using
> gettimeofday for the timer calibration is too expensive - it adds 1.5 seconds
> to our average boot time.  since many systems can use the 1/128 s - 1/64 s
> code or can determine their clocks statically (eg get it from firmware).
> 
> It's a tradeoff.  4 bytes of bloat versus 1.5 wasted seconds. (the actual code
> can be allocated in initmem).
> 
> Actually, if we start counting bytes, we might want to split up machvecs into
> initmem and permanent parts - but I'm not sure it's worth the obfuscation.
> 

Hmm, somebody please help me confirm this, but I'm almost certain (based
on all of the specs I've seen) that the Dreamcast CPU runs at 200MHz. 
Unfortunately I don't have the other specs (bus freq, etc.) in front of
me, but they're static as well (they're probably the standard SH4 ratio). 
I seriously doubt they would change in the future :).

Personally I'd rather lose the 1.5 seconds :)

M. R.