Messages in this thread | | | From | Dag-Erling Smørgrav <> | Subject | Re: [RFC+PATCH] RTC calibration | Date | Tue, 11 Sep 2007 18:04:06 +0200 |
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Clemens Koller <clemens.koller@anagramm.de> writes: > Dag-Erling Smørgrav <des@linpro.no> writes: > > Without knowing exacly which chip is present, there is no way for the > > userland calibration tool to know how big a difference a calibration > > step makes. > I am not talking about the calibration algorithm and it's quality.
Neither am I.
> I am talking about _how_ the calibration register is addressed from > userspace. It's a simple register, some bits at address 7 and I would > expect to read/modify/write registers to do all the things you want > to do. Register access in userspace doesn't put any limitation > to applications.
It requires the application to know the hardware intimately.
Calibration of the M41T11 is implemented using the lower 6 bits of register 7; this is not necessarily the case for other existing or future chips.
Let's say I normalize this to [-128;127]; an application that tried to speed up the clock would waste several hours increasing the calibration value from 0 to 1, 2, 3 before seeing an effect after increasing it to 4. And how do I normalize the assymetric range of the M41T11?
> Having only incs and decs without getting the actual value back seems > to be an absolutely unnecessary limitation here. > You cannot get the current value back to see if it's i.e. in saturation in > a way that it doesn't make sense to inc/decrement it further or in bigger steps > or reset it to zero...
The driver will return EINVAL if you try to increment or decrement the calibration register beyond its limits.
DES -- Dag-Erling Smørgrav Senior Software Developer Linpro AS - www.linpro.no - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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