Re: [PATCH v1 4/7] thermal: introduce the Power Allocator governor
From: Eduardo Valentin
Date: Tue Feb 24 2015 - 13:20:59 EST
Javi,
One minor clarification as follows:
On Wed, Jan 28, 2015 at 05:00:35PM +0000, Javi Merino wrote:
<big cut>
> +
> +k_d
> +---
> +
> +`k_d` configures the PID loop's derivative term constant. It's
> +recommended to leave it as the default: 0.
> +
I know we are considering K_d = 0. However, ...
<yet another big cut>
> + /*
> + * Calculate the derivative term
> + *
> + * We do err - prev_err, so with a positive k_d, a decreasing
> + * error (i.e. driving closer to the line) results in less
> + * power being applied, slowing down the controller)
> + */
> + d = mul_frac(tz->tzp->k_d, err - params->prev_err);
... Shouldn't the above d component consider the rate of changes over time of the error?
I would expect you should do:
d = k_d * (dE / dt)
or
d = K_d * ((err - params->prev_err) / sampling_period)
in plain C:
+ d = mul_frac(tz->tzp->k_d, err - params->prev_err);
+ d /= tz->passive_polling; /* might require fixed point division */
---
Eduardo Valentin
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