charge_ramp: initial commit of charge ramp module

Add new charge_ramp module which works with charge_manager to
slowly increase input current limit in order to find the optimal
charging current. To do this it looks for either VBUS drooping
too low or for the charger to over-current.

BUG=chrome-os-partner:34946
BRANCH=samus
TEST=tested with a variety of BC1.2 chargers, type-C only chargers,
and PD chargers to make sure we always stabilize charging at an
appropriate current limit.

Change-Id: Icc95aa2738ddb221f163f91c14a342a0674f9e0f
Signed-off-by: Alec Berg <alecaberg@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/247304
Reviewed-by: Vic Yang <victoryang@chromium.org>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>

9 files changed, 972 insertions, 4 deletions

diff --git a/common/build.mk b/common/build.mk
index 2f15725682..a6cb7bad8a 100644
--- a/common/build.mk
+++ b/common/build.mk
@@ -24,6 +24,7 @@ common-$(CONFIG_BUTTON_COUNT)+=button.o
 common-$(CONFIG_CAPSENSE)+=capsense.o
 common-$(CONFIG_CASE_CLOSED_DEBUG)+=case_closed_debug.o
 common-$(CONFIG_CHARGE_MANAGER)+=charge_manager.o
+common-$(CONFIG_CHARGE_RAMP)+=charge_ramp.o
 common-$(CONFIG_CHARGER)+=charger.o
 common-$(CONFIG_CHARGER_V1)+=charge_state_v1.o
 common-$(CONFIG_CHARGER_V2)+=charge_state_v2.o
diff --git a/common/charge_manager.c b/common/charge_manager.c
index bf93724cbd..da6b6c985c 100644
--- a/common/charge_manager.c
+++ b/common/charge_manager.c
@@ -5,6 +5,7 @@
 
 #include "adc.h"
 #include "charge_manager.h"
+#include "charge_ramp.h"
 #include "console.h"
 #include "gpio.h"
 #include "hooks.h"
@@ -26,6 +27,9 @@
 static struct charge_port_info available_charge[CHARGE_SUPPLIER_COUNT]
 					       [PD_PORT_COUNT];
 
+/* Keep track of when the supplier on each port is registered. */
+static timestamp_t registration_time[PD_PORT_COUNT];
+
 /*
  * Charge ceiling for ports. This can be set to temporarily limit the charge
  * pulled from a port, without influencing the port selection logic.
@@ -152,6 +156,13 @@ static void charge_manager_fill_power_info(int port,
 		r->meas.current_max = 0;
 		r->max_power = 0;
 	} else {
+#ifdef HAS_TASK_CHG_RAMP
+		/* Read ramped current if active charging port */
+		int use_ramp_current = (charge_port == port);
+#else
+		const int use_ramp_current = 0;
+#endif
+
 		switch (sup) {
 		case CHARGE_SUPPLIER_PD:
 			r->type = USB_CHG_TYPE_PD;
@@ -175,8 +186,16 @@ static void charge_manager_fill_power_info(int port,
 			r->type = USB_CHG_TYPE_OTHER;
 		}
 		r->meas.voltage_max = available_charge[sup][port].voltage;
-		r->meas.current_max = available_charge[sup][port].current;
-		r->max_power = POWER(available_charge[sup][port]);
+
+		if (use_ramp_current) {
+			r->meas.current_max = chg_ramp_get_current_limit();
+			r->max_power =
+				r->meas.current_max * r->meas.voltage_max;
+		} else {
+			r->meas.current_max =
+				available_charge[sup][port].current;
+			r->max_power = POWER(available_charge[sup][port]);
+		}
 
 		/*
 		 * If we are sourcing power, or sinking but not charging, then
@@ -385,9 +404,16 @@ static void charge_manager_refresh(void)
 			available_charge[new_supplier][new_port].voltage;
 	}
 
-	/* Change the charge limit + charge port if modified. */
-	if (new_port != charge_port || new_charge_current != charge_current) {
+	/* Change the charge limit + charge port/supplier if modified. */
+	if (new_port != charge_port || new_charge_current != charge_current ||
+	    new_supplier != charge_supplier) {
+#ifdef HAS_TASK_CHG_RAMP
+		chg_ramp_charge_supplier_change(
+				new_port, new_supplier, new_charge_current,
+				registration_time[new_port]);
+#else
 		board_set_charge_limit(new_charge_current);
+#endif
 		CPRINTS("CL: p%d s%d i%d v%d", new_port, new_supplier,
 			new_charge_current, new_charge_voltage);
 	}
@@ -508,6 +534,7 @@ static void charge_manager_make_change(enum charge_manager_change_type change,
 	if (change == CHANGE_CHARGE) {
 		available_charge[supplier][port].current = charge->current;
 		available_charge[supplier][port].voltage = charge->voltage;
+		registration_time[port] = get_time();
 
 		/*
 		 * If we have a charge on our delayed override port within
diff --git a/common/charge_ramp.c b/common/charge_ramp.c
new file mode 100644
index 0000000000..37bc45942d
--- /dev/null
+++ b/common/charge_ramp.c
@@ -0,0 +1,323 @@
+/* Copyright 2015 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Charge input current limit ramp module for Chrome EC */
+
+#include "charge_manager.h"
+#include "charge_ramp.h"
+#include "common.h"
+#include "console.h"
+#include "task.h"
+#include "timer.h"
+#include "usb_pd_config.h"
+#include "util.h"
+
+#define CPRINTS(format, args...) cprints(CC_USBCHARGE, format, ## args)
+
+/* Number of times to ramp current searching for limit before stable charging */
+#define RAMP_COUNT          3
+
+/*
+ * Time to delay for detecting the charger type (must be long enough for BC1.2
+ * driver to get supplier information and notify charge manager).
+ */
+#define CHARGE_DETECT_DELAY (2*SECOND)
+
+/* Maximum allowable time charger can be unplugged to be considered an OCP */
+#define OC_RECOVER_MAX_TIME (SECOND)
+
+/* Delay for running state machine when board is not consuming full current */
+#define CURRENT_DRAW_DELAY  (5*SECOND)
+
+/* Current ramp increment */
+#define RAMP_CURR_INCR_MA   64
+#define RAMP_CURR_DELAY     (500*MSEC)
+
+/* How much to backoff the input current limit when limit has been found */
+#define RAMP_ICL_BACKOFF    (2*RAMP_CURR_INCR_MA)
+
+/* Interval at which VBUS voltage is monitored in stable state */
+#define STABLE_VBUS_MONITOR_INTERVAL (SECOND)
+
+/* Time to delay for stablizing the charging current */
+#define STABLIZE_DELAY (5*SECOND)
+
+enum chg_ramp_state {
+	CHG_RAMP_DISCONNECTED,
+	CHG_RAMP_CHARGE_DETECT,
+	CHG_RAMP_OVERCURRENT_DETECT,
+	CHG_RAMP_RAMP,
+	CHG_RAMP_STABILIZE,
+	CHG_RAMP_STABLE,
+};
+static enum chg_ramp_state ramp_st;
+
+struct oc_info {
+	timestamp_t ts;
+	uint64_t recover;
+	int sup;
+	int icl;
+};
+
+/* OCP info for each over-current */
+static struct oc_info oc_info[PD_PORT_COUNT][RAMP_COUNT];
+static int oc_info_idx[PD_PORT_COUNT];
+#define ACTIVE_OC_INFO (oc_info[active_port][oc_info_idx[active_port]])
+
+/* Active charging information */
+static int active_port = CHARGE_PORT_NONE;
+static int active_sup;
+static int active_icl;
+static timestamp_t reg_time;
+
+static int stablize_port;
+static int stablize_sup;
+
+/* Maximum/minimum input current limit for active charger */
+static int max_icl;
+static int min_icl;
+
+
+void chg_ramp_charge_supplier_change(int port, int supplier, int current,
+				     timestamp_t registration_time)
+{
+	/*
+	 * If the last active port was a valid port and the port
+	 * has changed, then this may have been an over-current.
+	 */
+	if (active_port != CHARGE_PORT_NONE &&
+	    port != active_port) {
+		if (oc_info_idx[active_port] == RAMP_COUNT - 1)
+			oc_info_idx[active_port] = 0;
+		else
+			oc_info_idx[active_port]++;
+		ACTIVE_OC_INFO.ts = get_time();
+		ACTIVE_OC_INFO.sup = active_sup;
+		ACTIVE_OC_INFO.icl = active_icl;
+	}
+
+	/* Set new active port, set ramp state, and wake ramp task */
+	active_port = port;
+	active_sup = supplier;
+	min_icl = current;
+	max_icl = board_get_ramp_current_limit(active_sup);
+	reg_time = registration_time;
+	if (ramp_st != CHG_RAMP_STABILIZE) {
+		ramp_st = (active_port == CHARGE_PORT_NONE) ?
+			  CHG_RAMP_DISCONNECTED : CHG_RAMP_CHARGE_DETECT;
+		CPRINTS("Ramp reset: st%d\n", ramp_st);
+		task_wake(TASK_ID_CHG_RAMP);
+	}
+}
+
+int chg_ramp_get_current_limit(void)
+{
+	/*
+	 * If we are ramping or stable, then use the active input
+	 * current limit. Otherwise, use the minimum input current
+	 * limit.
+	 */
+	switch (ramp_st) {
+	case CHG_RAMP_RAMP:
+	case CHG_RAMP_STABILIZE:
+	case CHG_RAMP_STABLE:
+		return active_icl;
+	default:
+		return min_icl;
+	}
+}
+
+void chg_ramp_task(void)
+{
+	int task_wait_time = -1;
+	int i;
+	/*
+	 * Static initializer so that we don't clobber early calls to this
+	 * module.
+	 */
+	static enum chg_ramp_state ramp_st_prev = CHG_RAMP_DISCONNECTED,
+				   ramp_st_new = CHG_RAMP_DISCONNECTED;
+	int active_icl_new;
+
+	/* Clear last OCP supplier to guarantee we ramp on first connect */
+	for (i = 0; i < PD_PORT_COUNT; i++)
+		oc_info[i][0].sup = CHARGE_SUPPLIER_NONE;
+
+	while (1) {
+		ramp_st_new = ramp_st;
+		active_icl_new = active_icl;
+		switch (ramp_st) {
+		case CHG_RAMP_DISCONNECTED:
+			/* Do nothing */
+			task_wait_time = -1;
+			break;
+		case CHG_RAMP_CHARGE_DETECT:
+			/* Delay for charge_manager to determine supplier */
+			/* On entry to state, store the OC recovery time */
+			if (ramp_st_prev != ramp_st)
+				ACTIVE_OC_INFO.recover =
+					reg_time.val - ACTIVE_OC_INFO.ts.val;
+
+			/*
+			 * If we are not drawing full charge, then don't ramp,
+			 * just wait in this state, until we are.
+			 */
+			if (!board_is_consuming_full_charge()) {
+				task_wait_time = CURRENT_DRAW_DELAY;
+				break;
+			}
+
+			ramp_st_new = CHG_RAMP_OVERCURRENT_DETECT;
+			task_wait_time = CHARGE_DETECT_DELAY;
+			break;
+		case CHG_RAMP_OVERCURRENT_DETECT:
+			/* Check if we should ramp or go straight to stable */
+			task_wait_time = SECOND;
+
+			/* Skip ramp for specific suppliers */
+			if (!board_is_ramp_allowed(active_sup)) {
+				active_icl_new = min_icl;
+				ramp_st_new = CHG_RAMP_STABLE;
+				break;
+			}
+
+			/*
+			 * Compare recent OCP events, if all info matches,
+			 * then we don't need to ramp anymore.
+			 */
+			for (i = 0; i < RAMP_COUNT; i++) {
+				if (oc_info[active_port][i].sup != active_sup ||
+				    oc_info[active_port][i].recover >
+				    OC_RECOVER_MAX_TIME)
+					break;
+			}
+
+			if (i == RAMP_COUNT) {
+				/* Found OC threshold! */
+				active_icl_new = ACTIVE_OC_INFO.icl -
+						 RAMP_ICL_BACKOFF;
+				ramp_st_new = CHG_RAMP_STABLE;
+			} else {
+				/*
+				 * Need to ramp to find OC threshold, start
+				 * at the minimum input current limit.
+				 */
+				active_icl_new = min_icl;
+				ramp_st_new = CHG_RAMP_RAMP;
+			}
+			break;
+		case CHG_RAMP_RAMP:
+			/* Keep ramping until we find the limit */
+			task_wait_time = RAMP_CURR_DELAY;
+
+			/* Pause ramping if we are not drawing full current */
+			if (!board_is_consuming_full_charge()) {
+				task_wait_time = CURRENT_DRAW_DELAY;
+				break;
+			}
+
+			/* If VBUS is sagging a lot, then stop ramping */
+			if (board_is_vbus_too_low(CHG_RAMP_VBUS_RAMPING)) {
+				CPRINTS("VBUS low");
+				active_icl_new = MAX(min_icl, active_icl -
+							      RAMP_ICL_BACKOFF);
+				ramp_st_new = CHG_RAMP_STABILIZE;
+				task_wait_time = STABLIZE_DELAY;
+				stablize_port = active_port;
+				stablize_sup = active_sup;
+				break;
+			}
+
+			/* Ramp the current limit if we haven't reached max */
+			if (active_icl == max_icl)
+				ramp_st_new = CHG_RAMP_STABLE;
+			else if (active_icl + RAMP_CURR_INCR_MA > max_icl)
+				active_icl_new = max_icl;
+			else
+				active_icl_new = active_icl + RAMP_CURR_INCR_MA;
+			break;
+		case CHG_RAMP_STABILIZE:
+			/* Wait for current to stabilize after ramp is done */
+			/* Use default delay for exiting this state */
+			task_wait_time = SECOND;
+			if (active_port == stablize_port &&
+			    active_sup == stablize_sup) {
+				ramp_st_new = CHG_RAMP_STABLE;
+				break;
+			}
+
+			ramp_st_new = active_port == CHARGE_PORT_NONE ?
+				      CHG_RAMP_DISCONNECTED :
+				      CHG_RAMP_CHARGE_DETECT;
+			break;
+		case CHG_RAMP_STABLE:
+			/* Maintain input current limit */
+			/* On entry log charging stats */
+#ifdef CONFIG_USB_PD_LOGGING
+			if (ramp_st_prev != ramp_st)
+				charge_manager_save_log(active_port);
+#endif
+
+			/* Keep an eye on VBUS and restart ramping if it dips */
+			if (board_is_ramp_allowed(active_sup) &&
+			    board_is_vbus_too_low(CHG_RAMP_VBUS_STABLE)) {
+				CPRINTS("VBUS low; Re-ramp");
+				active_icl_new = min_icl;
+				ramp_st_new = CHG_RAMP_RAMP;
+			}
+			task_wait_time = STABLE_VBUS_MONITOR_INTERVAL;
+			break;
+		}
+		if (ramp_st != ramp_st_new || active_icl != active_icl_new)
+			CPRINTS("Ramp p%d st%d %dmA %dmA",
+				active_port, ramp_st_new, min_icl,
+				active_icl_new);
+
+		ramp_st_prev = ramp_st;
+		ramp_st = ramp_st_new;
+		active_icl = active_icl_new;
+
+		/* Set the input current limit */
+		board_set_charge_limit(chg_ramp_get_current_limit());
+
+		if (ramp_st == CHG_RAMP_STABILIZE)
+			/*
+			 * When in stabilize state, supplier/port may change
+			 * and we don't want to wake up task until we have
+			 * slept this amount of time.
+			 */
+			usleep(task_wait_time);
+		else
+			task_wait_event(task_wait_time);
+	}
+}
+
+#ifdef CONFIG_CMD_CHGRAMP
+static int command_chgramp(int argc, char **argv)
+{
+	int i;
+	int port;
+
+	ccprintf("Chg Ramp:\nState: %d\nMin ICL: %d\nActive ICL: %d\n",
+		 ramp_st, min_icl, active_icl);
+
+	for (port = 0; port < PD_PORT_COUNT; port++) {
+		ccprintf("Port %d:\n", port);
+		ccprintf("  OC idx:%d\n", oc_info_idx[port]);
+		for (i = 0; i < RAMP_COUNT; i++) {
+			ccprintf("  OC %d: s%d recover%lu icl%d\n", i,
+				 oc_info[port][i].sup,
+				 oc_info[port][i].recover,
+				 oc_info[port][i].icl);
+		}
+	}
+
+	return EC_SUCCESS;
+}
+DECLARE_CONSOLE_COMMAND(chgramp, command_chgramp,
+	"",
+	"Dump charge ramp state info",
+	NULL);
+#endif
diff --git a/include/charge_ramp.h b/include/charge_ramp.h
new file mode 100644
index 0000000000..629499e6ac
--- /dev/null
+++ b/include/charge_ramp.h
@@ -0,0 +1,82 @@
+/* Copyright 2015 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Charge input current limit ramp header for Chrome EC */
+
+#ifndef __CROS_EC_CHG_RAMP_H
+#define __CROS_EC_CHG_RAMP_H
+
+#include "timer.h"
+
+/* Charge ramp state used for checking VBUS */
+enum chg_ramp_vbus_state {
+	CHG_RAMP_VBUS_RAMPING,
+	CHG_RAMP_VBUS_STABLE
+};
+
+/**
+ * Check if ramping is allowed for given supplier
+ *
+ * @supplier Supplier to check
+ *
+ * @return Ramping is allowed for given supplier
+ */
+int board_is_ramp_allowed(int supplier);
+
+/**
+ * Get the maximum current limit that we are allowed to ramp to
+ *
+ * @supplier Active supplier type
+ *
+ * @return Maximum current in mA
+ */
+int board_get_ramp_current_limit(int supplier);
+
+/**
+ * Check if board is consuming full input current
+ *
+ * @return Board is consuming full input current
+ */
+int board_is_consuming_full_charge(void);
+
+/**
+ * Check if VBUS is too low
+ *
+ * @param ramp_state Current ramp state
+ *
+ * @return VBUS is sagging low
+ */
+int board_is_vbus_too_low(enum chg_ramp_vbus_state ramp_state);
+
+/**
+ * Get the input current limit set by ramp module
+ *
+ * Active input current limit (mA)
+ */
+int chg_ramp_get_current_limit(void);
+
+#ifdef HAS_TASK_CHG_RAMP
+/**
+ * Notify charge ramp module of supplier type change on a port. If port
+ * is CHARGE_PORT_NONE, the call indicates the last charge supplier went
+ * away.
+ *
+ * @port Active charging port
+ * @supplier Active charging supplier
+ * @current Minimum input current limit
+ * @registration_time Timestamp of when the supplier is registered
+ */
+void chg_ramp_charge_supplier_change(int port, int supplier, int current,
+				     timestamp_t registration_time);
+
+#else
+static inline void chg_ramp_charge_supplier_change(
+		int port, int supplier, timestamp_t registration_time) { }
+
+/* Point directly to board function to set charge limit */
+#define chg_ramp_set_min_current board_set_charge_limit
+#endif
+
+#endif /* __CROS_EC_CHG_RAMP_H */
diff --git a/include/config.h b/include/config.h
index af14aeae19..9e4e1999f7 100644
--- a/include/config.h
+++ b/include/config.h
@@ -215,6 +215,14 @@
 #undef CONFIG_CAPSENSE
 
 /*****************************************************************************/
+
+/* Compile charge manager */
+#undef CONFIG_CHARGE_MANAGER
+
+/* Compile input current ramping support */
+#undef CONFIG_CHARGE_RAMP
+
+/*****************************************************************************/
 /* Charger config */
 
 /* Compile common charge state code. You must pick an implementation. */
@@ -335,6 +343,7 @@
 #undef CONFIG_CMD_ACCELS
 #undef CONFIG_CMD_ACCEL_INFO
 #undef CONFIG_CMD_BATDEBUG
+#undef CONFIG_CMD_CHGRAMP
 #undef CONFIG_CMD_CLOCKGATES
 #undef CONFIG_CMD_COMXTEST
 #undef CONFIG_CMD_ECTEMP
diff --git a/test/build.mk b/test/build.mk
index 787e99a320..115fb515ee 100644
--- a/test/build.mk
+++ b/test/build.mk
@@ -36,6 +36,7 @@ test-list-host+=sbs_charging adapter host_command thermal_falco led_spring
 test-list-host+=bklight_lid bklight_passthru interrupt timer_dos button
 test-list-host+=motion_lid math_util sbs_charging_v2 battery_get_params_smart
 test-list-host+=lightbar inductive_charging usb_pd fan charge_manager
+test-list-host+=charge_ramp
 
 adapter-y=adapter.o
 battery_get_params_smart-y=battery_get_params_smart.o
@@ -43,6 +44,7 @@ bklight_lid-y=bklight_lid.o
 bklight_passthru-y=bklight_passthru.o
 button-y=button.o
 charge_manager-y=charge_manager.o
+charge_ramp-y+=charge_ramp.o
 console_edit-y=console_edit.o
 extpwr_gpio-y=extpwr_gpio.o
 flash-y=flash.o
diff --git a/test/charge_ramp.c b/test/charge_ramp.c
new file mode 100644
index 0000000000..e853b46e93
--- /dev/null
+++ b/test/charge_ramp.c
@@ -0,0 +1,502 @@
+/* Copyright 2015 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * Test AC input current ramp.
+ */
+
+#include "charge_manager.h"
+#include "charge_ramp.h"
+#include "common.h"
+#include "console.h"
+#include "gpio.h"
+#include "hooks.h"
+#include "task.h"
+#include "test_util.h"
+#include "timer.h"
+#include "util.h"
+
+#define TASK_EVENT_OVERCURRENT (1 << 0)
+
+#define RAMP_STABLE_DELAY (120*SECOND)
+
+/*
+ * Time to delay for detecting the charger type. This value follows
+ * the value in common/charge_ramp.c.
+ */
+#define CHARGE_DETECT_DELAY (2*SECOND)
+
+static int system_load_current_ma;
+static int vbus_low_current_ma = 500;
+static int overcurrent_current_ma = 3000;
+
+static int charge_limit_ma;
+
+/* Mock functions */
+
+int board_is_ramp_allowed(int supplier)
+{
+	/* Ramp for TEST4-TEST9 */
+	return supplier > CHARGE_SUPPLIER_TEST3;
+}
+
+int board_is_consuming_full_charge(void)
+{
+	return charge_limit_ma <= system_load_current_ma;
+}
+
+int board_is_vbus_too_low(enum chg_ramp_vbus_state ramp_state)
+{
+	return MIN(system_load_current_ma, charge_limit_ma) >
+	       vbus_low_current_ma;
+}
+
+void board_set_charge_limit(int limit_ma)
+{
+	charge_limit_ma = limit_ma;
+	if (charge_limit_ma > overcurrent_current_ma)
+		task_set_event(TASK_ID_TEST_RUNNER, TASK_EVENT_OVERCURRENT, 0);
+}
+
+int board_get_ramp_current_limit(int supplier)
+{
+	if (supplier == CHARGE_SUPPLIER_TEST9)
+		return 1600;
+	else if (supplier == CHARGE_SUPPLIER_TEST8)
+		return 2400;
+	else
+		return 3000;
+}
+
+/* Test utilities */
+
+static void plug_charger_with_ts(int supplier_type, int port, int min_current,
+				 int vbus_low_current, int overcurrent_current,
+				 timestamp_t reg_time)
+{
+	vbus_low_current_ma = vbus_low_current;
+	overcurrent_current_ma = overcurrent_current;
+	chg_ramp_charge_supplier_change(port, supplier_type, min_current,
+					reg_time);
+}
+
+static void plug_charger(int supplier_type, int port, int min_current,
+			 int vbus_low_current, int overcurrent_current)
+{
+	plug_charger_with_ts(supplier_type, port, min_current,
+			     vbus_low_current, overcurrent_current,
+			     get_time());
+}
+
+static void unplug_charger(void)
+{
+	chg_ramp_charge_supplier_change(CHARGE_PORT_NONE, CHARGE_SUPPLIER_NONE,
+					0, get_time());
+}
+
+static int unplug_charger_and_check(void)
+{
+	unplug_charger();
+	usleep(CHARGE_DETECT_DELAY);
+	return charge_limit_ma == 0;
+}
+
+static int wait_stable_no_overcurrent(void)
+{
+	return task_wait_event(RAMP_STABLE_DELAY) != TASK_EVENT_OVERCURRENT;
+}
+
+static int is_in_range(int x, int min, int max)
+{
+	return x >= min && x <= max;
+}
+
+/* Tests */
+
+static int test_no_ramp(void)
+{
+	system_load_current_ma = 3000;
+	/* A powerful charger, but hey, you're not allowed to ramp! */
+	plug_charger(CHARGE_SUPPLIER_TEST1, 0, 500, 3000, 3000);
+	usleep(CHARGE_DETECT_DELAY);
+	/* That's right. Start at 500 mA */
+	TEST_ASSERT(charge_limit_ma == 500);
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	/* ... and stays at 500 mA */
+	TEST_ASSERT(charge_limit_ma == 500);
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_full_ramp(void)
+{
+	system_load_current_ma = 3000;
+	/* Now you get to ramp with this 3A charger */
+	plug_charger(CHARGE_SUPPLIER_TEST4, 0, 500, 3000, 3000);
+	usleep(CHARGE_DETECT_DELAY);
+	/* Start with something around 500 mA */
+	TEST_ASSERT(is_in_range(charge_limit_ma, 500, 800));
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	/* And ramp up to 3A */
+	TEST_ASSERT(charge_limit_ma == 3000);
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_vbus_dip(void)
+{
+	system_load_current_ma = 3000;
+	/* VBUS dips too low right before the charger shuts down */
+	plug_charger(CHARGE_SUPPLIER_TEST5, 0, 1000, 1500, 1600);
+
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(is_in_range(charge_limit_ma, 1300, 1500));
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_overcurrent(void)
+{
+	system_load_current_ma = 3000;
+	/* Huh...VBUS doesn't dip before the charger shuts down */
+	plug_charger(CHARGE_SUPPLIER_TEST6, 0, 500, 3000, 1500);
+	usleep(CHARGE_DETECT_DELAY);
+	/* Ramp starts at 500 mA */
+	TEST_ASSERT(is_in_range(charge_limit_ma, 500, 700));
+
+	while (task_wait_event(RAMP_STABLE_DELAY) == TASK_EVENT_OVERCURRENT) {
+		/* Charger goes away but comes back after 0.6 seconds */
+		unplug_charger();
+		usleep(MSEC * 600);
+		plug_charger(CHARGE_SUPPLIER_TEST6, 0, 500, 3000, 1500);
+		usleep(CHARGE_DETECT_DELAY);
+		/* Ramp restarts at 500 mA */
+		TEST_ASSERT(is_in_range(charge_limit_ma, 500, 700));
+	}
+
+	TEST_ASSERT(is_in_range(charge_limit_ma, 1300, 1500));
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_switch_outlet(void)
+{
+	int i;
+
+	system_load_current_ma = 3000;
+	/* Here's a nice powerful charger */
+	plug_charger(CHARGE_SUPPLIER_TEST7, 0, 500, 3000, 3000);
+
+	/*
+	 * Now the user decides to move it to a nearby outlet...actually
+	 * he decides to move it 5 times!
+	 */
+	for (i = 0; i < 5; ++i) {
+		usleep(SECOND * 20);
+		unplug_charger();
+		usleep(SECOND * 1.5);
+		plug_charger(CHARGE_SUPPLIER_TEST7, 0, 500, 3000, 3000);
+		usleep(CHARGE_DETECT_DELAY);
+		/* Ramp restarts at 500 mA */
+		TEST_ASSERT(is_in_range(charge_limit_ma, 500, 700));
+	}
+
+	/* Should still ramp up to 3000 mA */
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(charge_limit_ma == 3000);
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_fast_switch(void)
+{
+	int i;
+
+	system_load_current_ma = 3000;
+	plug_charger(CHARGE_SUPPLIER_TEST4, 0, 500, 3000, 3000);
+
+	/*
+	 * Here comes that naughty user again, and this time he's switching
+	 * outlet really quickly. Fortunately this time he only does it twice.
+	 */
+	for (i = 0; i < 2; ++i) {
+		usleep(SECOND * 20);
+		unplug_charger();
+		usleep(600 * MSEC);
+		plug_charger(CHARGE_SUPPLIER_TEST4, 0, 500, 3000, 3000);
+		usleep(CHARGE_DETECT_DELAY);
+		/* Ramp restarts at 500 mA */
+		TEST_ASSERT(is_in_range(charge_limit_ma, 500, 700));
+	}
+
+	/* Should still ramp up to 3000 mA */
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(charge_limit_ma == 3000);
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_overcurrent_after_switch_outlet(void)
+{
+	system_load_current_ma = 3000;
+	/* Here's a less powerful charger */
+	plug_charger(CHARGE_SUPPLIER_TEST5, 0, 500, 3000, 1500);
+	usleep(SECOND * 5);
+
+	/* Now the user decides to move it to a nearby outlet */
+	unplug_charger();
+	usleep(SECOND * 1.5);
+	plug_charger(CHARGE_SUPPLIER_TEST5, 0, 500, 3000, 1500);
+
+	/* Okay the user is satisified */
+	while (task_wait_event(RAMP_STABLE_DELAY) == TASK_EVENT_OVERCURRENT) {
+		/* Charger goes away but comes back after 0.6 seconds */
+		unplug_charger();
+		usleep(MSEC * 600);
+		plug_charger(CHARGE_SUPPLIER_TEST5, 0, 500, 3000, 1500);
+		usleep(CHARGE_DETECT_DELAY);
+		/* Ramp restarts at 500 mA */
+		TEST_ASSERT(is_in_range(charge_limit_ma, 500, 700));
+	}
+
+	TEST_ASSERT(is_in_range(charge_limit_ma, 1300, 1500));
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_partial_load(void)
+{
+	/* We have a 3A charger, but we just want 1.5A */
+	system_load_current_ma = 1500;
+	plug_charger(CHARGE_SUPPLIER_TEST4, 0, 500, 3000, 2500);
+
+	/* We should end up with a little bit more than 1.5A */
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(is_in_range(charge_limit_ma, 1500, 1600));
+
+	/* Ok someone just started watching YouTube */
+	system_load_current_ma = 2000;
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(is_in_range(charge_limit_ma, 2000, 2100));
+
+	/* Somehow the system load increases again */
+	system_load_current_ma = 2600;
+	while (task_wait_event(RAMP_STABLE_DELAY) == TASK_EVENT_OVERCURRENT) {
+		/* Charger goes away but comes back after 0.6 seconds */
+		unplug_charger();
+		usleep(MSEC * 600);
+		plug_charger(CHARGE_SUPPLIER_TEST4, 0, 500, 3000, 2500);
+		usleep(CHARGE_DETECT_DELAY);
+		/* Ramp restarts at 500 mA */
+		TEST_ASSERT(is_in_range(charge_limit_ma, 500, 700));
+	}
+
+	/* Alright the charger isn't powerful enough, so we'll stop at 2.5A */
+	TEST_ASSERT(is_in_range(charge_limit_ma, 2300, 2500));
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_charge_supplier_stable(void)
+{
+	system_load_current_ma = 3000;
+	/* The charger says it's of type TEST4 initially */
+	plug_charger(CHARGE_SUPPLIER_TEST4, 0, 500, 1500, 1600);
+	/*
+	 * And then it decides it's actually TEST2 after 0.5 seconds,
+	 * why? Well, this charger is just evil.
+	 */
+	usleep(500 * MSEC);
+	plug_charger(CHARGE_SUPPLIER_TEST2, 0, 3000, 3000, 3000);
+	/* We should get 3A right away. */
+	usleep(SECOND);
+	TEST_ASSERT(charge_limit_ma == 3000);
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_charge_supplier_stable_ramp(void)
+{
+	system_load_current_ma = 3000;
+	/* This time we start with a non-ramp charge supplier */
+	plug_charger(CHARGE_SUPPLIER_TEST3, 0, 500, 3000, 3000);
+	/*
+	 * After 0.5 seconds, it's decided that the supplier is actually
+	 * a 1.5A ramp supplier.
+	 */
+	usleep(500 * MSEC);
+	plug_charger(CHARGE_SUPPLIER_TEST5, 0, 500, 1400, 1500);
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(is_in_range(charge_limit_ma, 1200, 1400));
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_charge_supplier_change(void)
+{
+	system_load_current_ma = 3000;
+	/* Start with a 3A ramp charge supplier */
+	plug_charger(CHARGE_SUPPLIER_TEST4, 0, 500, 3000, 3000);
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(charge_limit_ma == 3000);
+
+	/* The charger decides to change type to a 1.5A non-ramp supplier */
+	plug_charger(CHARGE_SUPPLIER_TEST1, 0, 1500, 3000, 3000);
+	usleep(500 * MSEC);
+	TEST_ASSERT(charge_limit_ma == 1500);
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(charge_limit_ma == 1500);
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_charge_port_change(void)
+{
+	system_load_current_ma = 3000;
+	/* Start with a 1.5A ramp charge supplier on port 0 */
+	plug_charger(CHARGE_SUPPLIER_TEST5, 0, 500, 1400, 1500);
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(is_in_range(charge_limit_ma, 1200, 1400));
+
+	/* Here comes a 2.1A ramp charge supplier on port 1 */
+	plug_charger(CHARGE_SUPPLIER_TEST6, 0, 500, 2000, 2100);
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(is_in_range(charge_limit_ma, 1800, 2000));
+
+	/* Now we have a 2.5A non-ramp charge supplier on port 0 */
+	plug_charger(CHARGE_SUPPLIER_TEST1, 0, 2500, 3000, 3000);
+	usleep(SECOND);
+	TEST_ASSERT(charge_limit_ma == 2500);
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(charge_limit_ma == 2500);
+
+	/* Unplug on port 0 */
+	plug_charger(CHARGE_SUPPLIER_TEST6, 0, 500, 2000, 2100);
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(is_in_range(charge_limit_ma, 1800, 2000));
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_vbus_shift(void)
+{
+	system_load_current_ma = 3000;
+	/*
+	 * At first, the charger is able to supply up to 1900 mA before
+	 * the VBUS voltage starts to drop.
+	 */
+	plug_charger(CHARGE_SUPPLIER_TEST7, 0, 500, 1900, 2000);
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(is_in_range(charge_limit_ma, 1700, 1900));
+
+	/* The charger heats up and VBUS voltage drops by 100mV */
+	vbus_low_current_ma = 1800;
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(is_in_range(charge_limit_ma, 1600, 1800));
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_equal_priority_overcurrent(void)
+{
+	int overcurrent_count = 0;
+	timestamp_t oc_time = get_time();
+
+	system_load_current_ma = 3000;
+
+	/*
+	 * Now we have two charge suppliers of equal priorties plugged into
+	 * port 0 and port 1. If the active one browns out, charge manager
+	 * switches to the other one.
+	 */
+	while (1) {
+		plug_charger_with_ts(CHARGE_SUPPLIER_TEST4, 0, 500, 3000,
+				     2000, oc_time);
+		oc_time = get_time();
+		oc_time.val += 600 * MSEC;
+		if (wait_stable_no_overcurrent())
+			break;
+		plug_charger_with_ts(CHARGE_SUPPLIER_TEST4, 1, 500, 3000,
+				     2000, oc_time);
+		oc_time = get_time();
+		oc_time.val += 600 * MSEC;
+		if (wait_stable_no_overcurrent())
+			break;
+		if (overcurrent_count++ >= 10) {
+			/*
+			 * Apparently we are in a loop and can never reach
+			 * stable state.
+			 */
+			unplug_charger();
+			return EC_ERROR_UNKNOWN;
+		}
+	}
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+static int test_ramp_limit(void)
+{
+	system_load_current_ma = 3000;
+
+	/* Plug in supplier that is limited to 1.6A */
+	plug_charger(CHARGE_SUPPLIER_TEST9, 0, 500, 3000, 3000);
+	usleep(SECOND);
+	TEST_ASSERT(is_in_range(charge_limit_ma, 500, 700));
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(charge_limit_ma == 1600);
+
+	/* Switch to supplier that is limited to 2.4A */
+	plug_charger(CHARGE_SUPPLIER_TEST8, 1, 500, 3000, 3000);
+	usleep(SECOND);
+	TEST_ASSERT(is_in_range(charge_limit_ma, 500, 700));
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(charge_limit_ma == 2400);
+
+	/* Go back to 1.6A limited, but VBUS goes low before that point */
+	plug_charger(CHARGE_SUPPLIER_TEST9, 0, 500, 1200, 1300);
+	usleep(SECOND);
+	TEST_ASSERT(is_in_range(charge_limit_ma, 500, 700));
+	TEST_ASSERT(wait_stable_no_overcurrent());
+	TEST_ASSERT(is_in_range(charge_limit_ma, 1000, 1200));
+
+	TEST_ASSERT(unplug_charger_and_check());
+	return EC_SUCCESS;
+}
+
+void run_test(void)
+{
+	test_reset();
+
+	RUN_TEST(test_no_ramp);
+	RUN_TEST(test_full_ramp);
+	RUN_TEST(test_vbus_dip);
+	RUN_TEST(test_overcurrent);
+	RUN_TEST(test_switch_outlet);
+	RUN_TEST(test_fast_switch);
+	RUN_TEST(test_overcurrent_after_switch_outlet);
+	RUN_TEST(test_partial_load);
+	RUN_TEST(test_charge_supplier_stable);
+	RUN_TEST(test_charge_supplier_stable_ramp);
+	RUN_TEST(test_charge_supplier_change);
+	RUN_TEST(test_charge_port_change);
+	RUN_TEST(test_vbus_shift);
+	RUN_TEST(test_equal_priority_overcurrent);
+	RUN_TEST(test_ramp_limit);
+
+	test_print_result();
+}
diff --git a/test/charge_ramp.tasklist b/test/charge_ramp.tasklist
new file mode 100644
index 0000000000..97a94fef6c
--- /dev/null
+++ b/test/charge_ramp.tasklist
@@ -0,0 +1,18 @@
+/* Copyright 2015 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/**
+ * List of enabled tasks in the priority order
+ *
+ * The first one has the lowest priority.
+ *
+ * For each task, use the macro TASK_TEST(n, r, d, s) where :
+ * 'n' in the name of the task
+ * 'r' in the main routine of the task
+ * 'd' in an opaque parameter passed to the routine at startup
+ * 's' is the stack size in bytes; must be a multiple of 8
+ */
+#define CONFIG_TEST_TASK_LIST \
+	TASK_TEST(CHG_RAMP, chg_ramp_task, NULL, SMALLER_TASK_STACK_SIZE)
diff --git a/test/test_config.h b/test/test_config.h
index 56fdf87772..c4bf3f57fa 100644
--- a/test/test_config.h
+++ b/test/test_config.h
@@ -139,5 +139,9 @@ int board_discharge_on_ac(int enabled);
 #define CONFIG_USB_PD_DUAL_ROLE
 #endif
 
+#ifdef TEST_CHARGE_RAMP
+#define CONFIG_CHARGE_RAMP
+#endif
+
 #endif  /* TEST_BUILD */
 #endif  /* __CROS_EC_TEST_CONFIG_H */