On Thu, 23 Oct 2008 21:38:48 +0400, Sergei Shtylyov <sshtylyov@xxxxxxxxxxxxx> wrote: > > + unsigned int sp = (cr >> 4) & 3; > > + unsigned int clock = gbus_clock / (4 - sp); > > + unsigned int cycle = 1000000000 / clock; > > Hm, couldn't all these values be calculated only once? > > > + unsigned int wt, shwt; > > + > > + /* Minimum DIOx- active time */ > > + wt = DIV_ROUND_UP(t->act8b, cycle) - 2; > > + /* IORDY setup time: 35ns */ > > + wt = max(wt, DIV_ROUND_UP(35, cycle)); > > Same comment about calculating only once... Yes. But are there any good place to hold calculated values? I don't think it is not worth to allocate a local structure just for holding such values. And this is not a critical path anyway :-) > > + /* actual wait-cycle is max(wt & ~1, 1) */ > > + if (wt > 2 && (wt & 1)) > > + wt++; > > + wt &= ~1; > > + /* Address-valid to DIOR/DIOW setup */ > > It's really address valid to -CSx assertion and -CSx to -DIOx assertion > setup time, and contrarywise, -DIOx to -CSx release and -CSx release to > address invalid hold time, so it actualy applies 4 times and so constitutes > -DIOx recovery time. It's worth to check if the minimum cycle time is reached > with the setup time -- for PIO mode 0, minimum setup is 70 ns, multiplying > that by 4 gives 280 ns recovery and adding 290 ns active time gives 570 ns > cycle while the minimum is 600 ns. Luckily, PIO0 seems the only problematic > mode as I doubt that EBUS controller can do back-to-back IDE reads/writes > keeping address and/or -CSx asserted in-between amounting to recovery time > being only 2x/3x setup times -- in the worst, 2x case PIO mode 3 would also > have too little cycle/recovery time... Oh I had not considered the total cycle time at all... I agree with your analysis that PIO0 is the only problematic case. And I also noticed that the calculated shwt value can be begger than 7 (which is max SHWT value) on fast GBUS and slow drive. I will add some check for it. I'll address all other issues too (and send incremental patch). Thanks! --- Atsushi Nemoto
