atlas: enable discharge-on-ac

enable a mode where we will switch from AC power to battery power when
the battery is fully charged.  then, when the battery is no longer
considred fully charged (95%), switch back to AC and chrage the
battery.

BUG=b:128709632
BRANCH=none
TEST=observed atlas hovers between 95% and 100% battery charge.  no
	AC current drawn while going from 100% to 95%.

Change-Id: I6e22189fa5be43dc31a5c3b93fda70a4fe5958a1
Signed-off-by: Caveh Jalali <caveh@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1496755
Commit-Ready: Caveh Jalali <caveh@google.com>
Tested-by: caveh jalali <caveh@chromium.org>
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>

1 files changed, 41 insertions, 0 deletions

diff --git a/board/atlas/battery.c b/board/atlas/battery.c
index 806f042a70..fb2fba18be 100644
--- a/board/atlas/battery.c
+++ b/board/atlas/battery.c
@@ -155,11 +155,52 @@ int board_cut_off_battery(void)
 	return rv ? EC_RES_ERROR : EC_RES_SUCCESS;
 }
 
+static int charger_should_discharge_on_ac(struct charge_state_data *curr)
+{
+	/* Can not discharge on AC without battery */
+	if (curr->batt.is_present != BP_YES)
+		return 0;
+	if (curr->batt.flags & BATT_FLAG_BAD_STATUS)
+		return 0;
+
+	/* Do not discharge on AC if the battery is still waking up */
+	if (!(curr->batt.flags & BATT_FLAG_WANT_CHARGE) &&
+	    !(curr->batt.status & STATUS_FULLY_CHARGED))
+		return 0;
+
+	/*
+	 * In light load (<450mA being withdrawn from VSYS) the DCDC of the
+	 * charger operates intermittently i.e. DCDC switches continuously
+	 * and then stops to regulate the output voltage and current, and
+	 * sometimes to prevent reverse current from flowing to the input.
+	 * This causes a slight voltage ripple on VSYS that falls in the
+	 * audible noise frequency (single digit kHz range). This small
+	 * ripple generates audible noise in the output ceramic capacitors
+	 * (caps on VSYS and any input of DCDC under VSYS).
+	 *
+	 * To overcome this issue enable the battery learning operation
+	 * and suspend USB charging and DC/DC converter.
+	 */
+	if (!battery_is_cut_off() &&
+	    !(curr->batt.flags & BATT_FLAG_WANT_CHARGE) &&
+		(curr->batt.status & STATUS_FULLY_CHARGED))
+		return 1;
+
+	return 0;
+}
+
 int charger_profile_override(struct charge_state_data *curr)
 {
 	const struct battery_info *batt_info;
 	/* battery temp in 0.1 deg C */
 	int bat_temp_c;
+	int disch_on_ac = charger_should_discharge_on_ac(curr);
+
+	charger_discharge_on_ac(disch_on_ac);
+	if (disch_on_ac) {
+		curr->state = ST_DISCHARGE;
+		return 0;
+	}
 
 	if (curr->batt.flags & BATT_FLAG_BAD_TEMPERATURE)
 		return 0;