Hi folks! I am writing to propose a patch for UPower. I have a broken battery (or ACPI, or what it is, I really don't know) and it doesn't report energy-rate. From the last version UPower is able to compute the discharge (or charge) rate by sampling the energy over time, that is a really nice feature for me!
The thing is that only two points are used to compute this rate, and so the time estimate is quite going up and down. I thought it would be nice to use a simple linear regression [1] to determine the rate, so I wrote a patch to the test the idea, and it is working for me. Do you think the patch could be included upstream? I think that many broken-batteries people would be glad to have a consistent estimate of the remaining lifetime. I understand, though, that this change make the rate change slowly in response to some events (like starting heavy computations or so...) but I still think that taking the average on some more points is nicer. I'm attaching the patch to this email. P.S.: The memmove() call are not the best way to handle prepending new entries in the array; if you think it's nicer I could write a simple circular buffer to store energy_old values and timespecs. Thanks again for your work :) [1]: http://en.wikipedia.org/wiki/Linear_regression -- Leonardo Robol <l...@robol.it>
diff --git a/src/linux/up-device-supply.c b/src/linux/up-device-supply.c
index 9b29713..6e21531 100644
--- a/src/linux/up-device-supply.c
+++ b/src/linux/up-device-supply.c
@@ -45,13 +45,15 @@
#define UP_DEVICE_SUPPLY_COLDPLUG_UNITS_CHARGE TRUE
#define UP_DEVICE_SUPPLY_COLDPLUG_UNITS_ENERGY FALSE
+#define UP_DEVICE_SUPPLY_ENERGY_OLD_LENGTH 4 /* Number of old energy values to keep cached */
+
struct UpDeviceSupplyPrivate
{
guint poll_timer_id;
gboolean has_coldplug_values;
gboolean coldplug_units;
- gdouble energy_old;
- GTimeVal energy_old_timespec;
+ gdouble *energy_old;
+ GTimeVal *energy_old_timespec;
gdouble rate_old;
guint unknown_retries;
gboolean enable_poll;
@@ -118,12 +120,17 @@ static void
up_device_supply_reset_values (UpDeviceSupply *supply)
{
UpDevice *device = UP_DEVICE (supply);
+ guint i;
supply->priv->has_coldplug_values = FALSE;
supply->priv->coldplug_units = UP_DEVICE_SUPPLY_COLDPLUG_UNITS_ENERGY;
supply->priv->rate_old = 0;
- supply->priv->energy_old = 0;
- supply->priv->energy_old_timespec.tv_sec = 0;
+
+ for (i = 0; i < UP_DEVICE_SUPPLY_ENERGY_OLD_LENGTH; ++i)
+ {
+ supply->priv->energy_old[i] = 0.0;
+ supply->priv->energy_old_timespec[i].tv_sec = 0;
+ }
/* reset to default */
g_object_set (device,
@@ -240,36 +247,96 @@ up_device_supply_get_online (UpDevice *device, gboolean *online)
}
/**
+ * up_device_supply_push_new_energy:
+ *
+ * Store the new energy in the list of old energies of the supply, so
+ * it can be used to determine the energy rate.
+ */
+static gboolean
+up_device_supply_push_new_energy (UpDeviceSupply * supply, gdouble energy)
+{
+ /* Check if the energy value has changed and, if that's the case,
+ * store the new values in the buffer. */
+ if (supply->priv->energy_old[0] != energy)
+ {
+ /* Move old values of energy_old forward */
+ g_memmove (supply->priv->energy_old + 1,
+ supply->priv->energy_old,
+ (UP_DEVICE_SUPPLY_ENERGY_OLD_LENGTH - 1) * sizeof (gdouble));
+ g_memmove (supply->priv->energy_old_timespec + 1,
+ supply->priv->energy_old_timespec,
+ (UP_DEVICE_SUPPLY_ENERGY_OLD_LENGTH - 1) * sizeof (GTimeVal));
+
+ supply->priv->energy_old[0] = energy;
+ g_get_current_time (&supply->priv->energy_old_timespec[0]);
+
+ return TRUE;
+ }
+
+ return FALSE;
+}
+
+/**
* up_device_supply_calculate_rate:
**/
static gdouble
up_device_supply_calculate_rate (UpDeviceSupply *supply, gdouble energy)
{
- guint time_s;
+ gdouble rate;
+ gdouble sum_x;
GTimeVal now;
+ int i;
+
+ /* get the time difference from now and use linear regression to determine
+ * the discharge rate of the battery. */
+ g_get_current_time (&now);
+
+ /* Store the data on the new energy received */
+ up_device_supply_push_new_energy (supply, energy);
if (energy < 0.1f)
return 0.0f;
-
- if (supply->priv->energy_old < 0.1f)
+
+ if (supply->priv->energy_old[0] < 0.1f)
return 0.0f;
- if (supply->priv->energy_old - energy < 0.01)
- return supply->priv->rate_old;
+ /* Discharge rate */
+ rate = 0;
+
+ /* Used to compute the sum of the squared times difference */
+ sum_x = 0;
+
+ /* Don't use the new point obtained since it may cause instability in the
+ * estimate */
+ now = supply->priv->energy_old_timespec[0];
+ for (i = 1; i < UP_DEVICE_SUPPLY_ENERGY_OLD_LENGTH; i++)
+ {
+ /* Only use this value if it seems valid */
+ if (supply->priv->energy_old_timespec[i].tv_sec && supply->priv->energy_old[i])
+ {
+ /* This is the square of t_i^2 */
+ sum_x += (now.tv_sec - supply->priv->energy_old_timespec[i].tv_sec) *
+ (now.tv_sec - supply->priv->energy_old_timespec[i].tv_sec);
+
+ /* Sum the module of the energy difference */
+ rate += fabs ((supply->priv->energy_old_timespec[i].tv_sec - now.tv_sec) *
+ (energy - supply->priv->energy_old[i]));
+ }
+ }
- /* get the time difference */
- g_get_current_time (&now);
- time_s = now.tv_sec - supply->priv->energy_old_timespec.tv_sec;
- if (time_s == 0)
+ if (sum_x == 0)
return supply->priv->rate_old;
- /* get the difference in charge */
- energy = fabs (supply->priv->energy_old - energy);
- if (energy < 0.1f)
+ /* Compute the discharge per hour, and not per second */
+ rate /= sum_x / 3600.0;
+
+ /* If the rate is zero, use the old rate. It will usually happens if no data
+ * are in the buffer yet. If the rate is too high, i.e. more than 100W,
+ * don't use it. */
+ if (rate == 0 || rate > 100)
return supply->priv->rate_old;
- /* probably okay */
- return energy * 3600.0 / time_s;
+ return rate;
}
/**
@@ -719,17 +786,21 @@ up_device_supply_refresh_battery (UpDeviceSupply *supply)
if (time_to_full > (20 * 60 * 60))
time_to_full = 0;
- /* set the old status if it hasn't changed */
- if (supply->priv->energy_old != energy) {
- supply->priv->energy_old = energy;
+ /* Check if the energy value has changed and, if that's the case,
+ * store the new values in the buffer. */
+ if (up_device_supply_push_new_energy (supply, energy))
supply->priv->rate_old = energy_rate;
- g_get_current_time (&supply->priv->energy_old_timespec);
- }
/* we changed state */
g_object_get (device, "state", &old_state, NULL);
if (old_state != state)
- supply->priv->energy_old = 0;
+ {
+ for (i = 0; i < UP_DEVICE_SUPPLY_ENERGY_OLD_LENGTH; ++i)
+ {
+ supply->priv->energy_old[i] = 0;
+ supply->priv->energy_old_timespec[i].tv_sec = 0;
+ }
+ }
g_object_set (device,
"energy", energy,
@@ -919,6 +990,10 @@ up_device_supply_init (UpDeviceSupply *supply)
supply->priv->unknown_retries = 0;
supply->priv->poll_timer_id = 0;
supply->priv->enable_poll = TRUE;
+
+ /* Allocate the space for the stats on the battery charging - discharging */
+ supply->priv->energy_old = g_malloc_n (UP_DEVICE_SUPPLY_ENERGY_OLD_LENGTH, sizeof (gdouble));
+ supply->priv->energy_old_timespec = g_malloc_n (UP_DEVICE_SUPPLY_ENERGY_OLD_LENGTH, sizeof (GTimeVal));
}
/**
@@ -938,6 +1013,9 @@ up_device_supply_finalize (GObject *object)
if (supply->priv->poll_timer_id > 0)
g_source_remove (supply->priv->poll_timer_id);
+ g_free (supply->priv->energy_old);
+ g_free (supply->priv->energy_old_timespec);
+
G_OBJECT_CLASS (up_device_supply_parent_class)->finalize (object);
}
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