brask: power_monitor functionality

Integrate power_monitor code from Puff into the Brask design.

BUG=b:219632035
BRANCH=None
TEST=make BOARD=brask, flashed, adc PPVAR_IMON visible

Change-Id: I7f1af8bfb401b7a3bc9a8231838a1e4ca9360cd7
Signed-off-by: Daniel Coggin <dcoggin@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3463083
Reviewed-by: Andrew McRae <amcrae@google.com>

5 files changed, 428 insertions, 10 deletions

diff --git a/board/brask/board.c b/board/brask/board.c
index 7fb0162d17..43d7939e2d 100644
--- a/board/brask/board.c
+++ b/board/brask/board.c
@@ -3,6 +3,7 @@
  * found in the LICENSE file.
  */
 
+#include "adc.h"
 #include "assert.h"
 #include "button.h"
 #include "charge_manager.h"
@@ -19,13 +20,16 @@
 #include "switch.h"
 #include "throttle_ap.h"
 #include "usbc_config.h"
-
-#include "gpio_list.h" /* Must come after other header files. */
+#include "usbc_ppc.h"
+#include "driver/tcpm/tcpci.h"
 
 /* Console output macros */
 #define CPRINTF(format, args...) cprintf(CC_CHARGER, format, ## args)
 #define CPRINTS(format, args...) cprints(CC_CHARGER, format, ## args)
 
+static void power_monitor(void);
+DECLARE_DEFERRED(power_monitor);
+
 /******************************************************************************/
 /* USB-A charging control */
 
@@ -100,10 +104,92 @@ int board_set_active_charge_port(int port)
 	return EC_SUCCESS;
 }
 
-void board_set_charge_limit(int port, int supplier, int charge_ma,
-				int max_ma, int charge_mv)
+static uint8_t usbc_overcurrent;
+static int32_t base_5v_power_s5;
+static int32_t base_5v_power_z1;
+
+/*
+ * Power usage for each port as measured or estimated.
+ * Units are milliwatts (5v x ma current)
+ */
+
+/* PP5000_S5 loads */
+#define PWR_S5_BASE_LOAD  (5*1431)
+#define PWR_S5_FRONT_HIGH (5*1737)
+#define PWR_S5_FRONT_LOW  (5*1055)
+#define PWR_S5_REAR_HIGH  (5*1737)
+#define PWR_S5_REAR_LOW   (5*1055)
+#define PWR_S5_HDMI       (5*580)
+#define PWR_S5_MAX        (5*10000)
+#define FRONT_DELTA       (PWR_S5_FRONT_HIGH - PWR_S5_FRONT_LOW)
+#define REAR_DELTA        (PWR_S5_REAR_HIGH - PWR_S5_REAR_LOW)
+
+/* PP5000_Z1 loads */
+#define PWR_Z1_BASE_LOAD   (5*5)
+#define PWR_Z1_C_HIGH      (5*3600)
+#define PWR_Z1_C_LOW       (5*2000)
+#define PWR_Z1_MAX         (5*9000)
+/*
+ * Update the 5V power usage, assuming no throttling,
+ * and invoke the power monitoring.
+ */
+static void update_5v_usage(void)
 {
+	int front_ports = 0;
+	int rear_ports = 0;
+
+	/*
+	 * Recalculate the 5V load, assuming no throttling.
+	 */
+	base_5v_power_s5 = PWR_S5_BASE_LOAD;
+	if (!gpio_get_level(GPIO_USB_A0_OC_ODL)) {
+		front_ports++;
+		base_5v_power_s5 += PWR_S5_FRONT_LOW;
+	}
+	if (!gpio_get_level(GPIO_USB_A1_OC_ODL)) {
+		front_ports++;
+		base_5v_power_s5 += PWR_S5_FRONT_LOW;
+	}
+	/*
+	 * Only 1 front port can run higher power at a time.
+	 */
+	if (front_ports > 0)
+		base_5v_power_s5 += PWR_S5_FRONT_HIGH - PWR_S5_FRONT_LOW;
+
+	if (!gpio_get_level(GPIO_USB_A2_OC_ODL)) {
+		front_ports++;
+		base_5v_power_s5 += PWR_S5_REAR_LOW;
+	}
+	if (!gpio_get_level(GPIO_USB_A3_OC_ODL)) {
+		front_ports++;
+		base_5v_power_s5 += PWR_S5_REAR_LOW;
+	}
+	/*
+	 * Only 1 rear port can run higher power at a time.
+	 */
+	if (rear_ports > 0)
+		base_5v_power_s5 += PWR_S5_REAR_HIGH - PWR_S5_REAR_LOW;
+	if (!gpio_get_level(GPIO_HDMI_CONN_OC_ODL))
+		base_5v_power_s5 += PWR_S5_HDMI;
+	base_5v_power_z1 = PWR_Z1_BASE_LOAD;
+	if (usbc_overcurrent)
+		base_5v_power_z1 += PWR_Z1_C_HIGH;
+	/*
+	 * Invoke the power handler immediately.
+	 */
+	hook_call_deferred(&power_monitor_data, 0);
 }
+DECLARE_DEFERRED(update_5v_usage);
+/*
+ * Start power monitoring after ADCs have been initialised.
+ */
+DECLARE_HOOK(HOOK_INIT, update_5v_usage, HOOK_PRIO_INIT_ADC + 1);
+
+static void port_ocp_interrupt(enum gpio_signal signal)
+{
+	hook_call_deferred(&update_5v_usage_data, 0);
+}
+#include "gpio_list.h" /* Must come after other header files. */
 
 /******************************************************************************/
 /*
@@ -195,5 +281,318 @@ DECLARE_HOOK(HOOK_INIT, adp_state_init, HOOK_PRIO_CHARGE_MANAGER_INIT + 1);
 static void board_init(void)
 {
 	gpio_enable_interrupt(GPIO_BJ_ADP_PRESENT_ODL);
+	gpio_enable_interrupt(GPIO_HDMI_CONN_OC_ODL);
+	gpio_enable_interrupt(GPIO_USB_A0_OC_ODL);
+	gpio_enable_interrupt(GPIO_USB_A1_OC_ODL);
+	gpio_enable_interrupt(GPIO_USB_A2_OC_ODL);
+	gpio_enable_interrupt(GPIO_USB_A3_OC_ODL);
 }
 DECLARE_HOOK(HOOK_INIT, board_init, HOOK_PRIO_DEFAULT);
+
+void board_overcurrent_event(int port, int is_overcurrented)
+{
+	/* Check that port number is valid. */
+	if ((port < 0) || (port >= CONFIG_USB_PD_PORT_MAX_COUNT))
+		return;
+	usbc_overcurrent = is_overcurrented;
+	update_5v_usage();
+}
+/*
+ * Power monitoring and management.
+ *
+ * the power budgets are met without letting the system fall into
+ * power deficit (perhaps causing a brownout).
+ *
+ * There are 2 power budgets that need to be managed:
+ * The overall goal is to gracefully manage the power demand so that
+ *  - overall system power as measured on the main power supply rail.
+ *  - 5V power delivered to the USB and HDMI ports.
+ *
+ * The actual system power demand is calculated from the VBUS voltage and
+ * the input current (read from a shunt), averaged over 5 readings.
+ * The power budget limit is from the charge manager.
+ *
+ * The 5V power cannot be read directly. Instead, we rely on overcurrent
+ * inputs from the USB and HDMI ports to indicate that the port is in use
+ * (and drawing maximum power).
+ *
+ * There are 3 throttles that can be applied (in priority order):
+ *
+ *  - Type A BC1.2 front port restriction (3W)
+ *  - Type A BC1.2 rear port restriction (3W)
+ *  - Type C PD (throttle to 1.5A if sourcing)
+ *  - Turn on PROCHOT, which immediately throttles the CPU.
+ *
+ *  The first 3 throttles affect both the system power and the 5V rails.
+ *  The third is a last resort to force an immediate CPU throttle to
+ *  reduce the overall power use.
+ *
+ *  The strategy is to determine what the state of the throttles should be,
+ *  and to then turn throttles off or on as needed to match this.
+ *
+ *  This function runs on demand, or every 2 ms when the CPU is up,
+ *  and continually monitors the power usage, applying the
+ *  throttles when necessary.
+ *
+ *  All measurements are in milliwatts.
+ */
+#define THROT_TYPE_A_FRONT  BIT(0)
+#define THROT_TYPE_A_REAR   BIT(1)
+#define THROT_TYPE_C0       BIT(2)
+#define THROT_TYPE_C1       BIT(3)
+#define THROT_TYPE_C2       BIT(4)
+#define THROT_PROCHOT       BIT(5)
+
+/*
+ * Power gain if front USB A ports are limited.
+ */
+#define POWER_GAIN_TYPE_A	3200
+/*
+ * Power gain if Type C port is limited.
+ */
+#define POWER_GAIN_TYPE_C	8800
+/*
+ * Power is averaged over 10 ms, with a reading every 2 ms.
+ */
+#define POWER_DELAY_MS		2
+#define POWER_READINGS		(10/POWER_DELAY_MS)
+
+static void power_monitor(void)
+{
+	static uint32_t current_state;
+	static uint32_t history[POWER_READINGS];
+	static uint8_t index;
+	int32_t delay;
+	uint32_t new_state = 0, diff;
+	int32_t headroom_5v_s5 = PWR_S5_MAX - base_5v_power_s5;
+	int32_t headroom_5v_z1 = PWR_Z1_MAX - base_5v_power_z1;
+
+	/*
+	 * If CPU is off or suspended, no need to throttle
+	 * or restrict power.
+	 */
+	if (chipset_in_state(CHIPSET_STATE_ANY_OFF |
+			     CHIPSET_STATE_SUSPEND)) {
+		/*
+		 * Slow down monitoring, assume no throttling required.
+		 */
+		delay = 20 * MSEC;
+		/*
+		 * Clear the first entry of the power table so that
+		 * it is re-initilalised when the CPU starts.
+		 */
+		history[0] = 0;
+	} else {
+		int32_t charger_mw;
+
+		delay = POWER_DELAY_MS * MSEC;
+		/*
+		 * Get current charger limit (in mw).
+		 * If not configured yet, skip.
+		 */
+		charger_mw = charge_manager_get_power_limit_uw() / 1000;
+		if (charger_mw != 0) {
+			int32_t gap, total, max, power;
+			int i;
+
+			/*
+			 * Read power usage.
+			 */
+			power = (adc_read_channel(ADC_VBUS) *
+				 adc_read_channel(ADC_PPVAR_IMON)) /
+				 1000;
+			/* Init power table */
+			if (history[0] == 0) {
+				for (i = 0; i < POWER_READINGS; i++)
+					history[i] = power;
+			}
+			/*
+			 * Update the power readings and
+			 * calculate the average and max.
+			 */
+			history[index] = power;
+			index = (index + 1) % POWER_READINGS;
+			total = 0;
+			max = history[0];
+			for (i = 0; i < POWER_READINGS; i++) {
+				total += history[i];
+				if (history[i] > max)
+					max = history[i];
+			}
+			/*
+			 * For Type-C power supplies, there is
+			 * less tolerance for exceeding the rating,
+			 * so use the max power that has been measured
+			 * over the measuring period.
+			 * For barrel-jack supplies, the rating can be
+			 * exceeded briefly, so use the average.
+			 */
+			if (charge_manager_get_supplier() ==
+			    CHARGE_SUPPLIER_PD)
+				power = max;
+			else
+				power = total / POWER_READINGS;
+			/*
+			 * Calculate gap, and if negative, power
+			 * demand is exceeding configured power budget, so
+			 * throttling is required to reduce the demand.
+			 */
+			gap = charger_mw - power;
+			/*
+			 * Limiting type-A power rear ports.
+			 */
+			if (gap <= 0) {
+				new_state |= THROT_TYPE_A_REAR;
+				headroom_5v_s5 += REAR_DELTA;
+				if (!(current_state & THROT_TYPE_A_REAR))
+					gap += POWER_GAIN_TYPE_A;
+			}
+			/*
+			 * Limiting type-A power front ports.
+			 */
+			if (gap <= 0) {
+				new_state |= THROT_TYPE_A_FRONT;
+				headroom_5v_s5 += FRONT_DELTA;
+				if (!(current_state & THROT_TYPE_A_REAR))
+					gap += POWER_GAIN_TYPE_A;
+			}
+			/*
+			 * If the type-C port is sourcing power,
+			 * check whether it should be throttled.
+			 */
+			if (ppc_is_sourcing_vbus(0) && gap <= 0) {
+				new_state |= THROT_TYPE_C0;
+				headroom_5v_z1 += PWR_Z1_C_HIGH - PWR_Z1_C_LOW;
+				if (!(current_state & THROT_TYPE_C0))
+					gap += POWER_GAIN_TYPE_C;
+			}
+			/*
+			 * If the type-C port is sourcing power,
+			 * check whether it should be throttled.
+			 */
+			if (ppc_is_sourcing_vbus(1) && gap <= 0) {
+				new_state |= THROT_TYPE_C1;
+				headroom_5v_z1 += PWR_Z1_C_HIGH - PWR_Z1_C_LOW;
+				if (!(current_state & THROT_TYPE_C1))
+					gap += POWER_GAIN_TYPE_C;
+			}
+			/*
+			 * If the type-C port is sourcing power,
+			 * check whether it should be throttled.
+			 */
+			if (ppc_is_sourcing_vbus(2) && gap <= 0) {
+				new_state |= THROT_TYPE_C2;
+				headroom_5v_z1 += PWR_Z1_C_HIGH - PWR_Z1_C_LOW;
+				if (!(current_state & THROT_TYPE_C2))
+					gap += POWER_GAIN_TYPE_C;
+			}
+			/*
+			 * As a last resort, turn on PROCHOT to
+			 * throttle the CPU.
+			 */
+			if (gap <= 0)
+				new_state |= THROT_PROCHOT;
+		}
+	}
+	/*
+	 * Check the 5v power usage and if necessary,
+	 * adjust the throttles in priority order.
+	 *
+	 * Either throttle may have already been activated by
+	 * the overall power control.
+	 *
+	 * We rely on the overcurrent detection to inform us
+	 * if the port is in use.
+	 *
+	 *  - If type C not already throttled:
+	 *	* If not overcurrent, prefer to limit type C [1].
+	 *	* If in overcurrentuse:
+	 *		- limit type A first [2]
+	 *		- If necessary, limit type C [3].
+	 *  - If type A not throttled, if necessary limit it [2].
+	 */
+	if (headroom_5v_z1 < 0) {
+		/*
+		 * Check whether type C is not throttled,
+		 * and is not overcurrent.
+		 */
+		if (!((new_state & THROT_TYPE_C0) || usbc_overcurrent)) {
+			/*
+			 * [1] Type C not in overcurrent, throttle it.
+			 */
+			headroom_5v_z1 += PWR_Z1_C_HIGH - PWR_Z1_C_LOW;
+			new_state |= THROT_TYPE_C0;
+		}
+		/*
+		 * [2] If still under-budget, limit type C.
+		 * No need to check if it is already throttled or not.
+		 */
+		if (headroom_5v_z1 < 0)
+			new_state |= THROT_TYPE_C0;
+	}
+	if (headroom_5v_s5 < 0) {
+		/*
+		 * [1] If type A rear not already throttled, and power still
+		 * needed, limit type A rear.
+		 */
+		if (!(new_state & THROT_TYPE_A_REAR) && headroom_5v_s5 < 0) {
+			headroom_5v_s5 += PWR_S5_REAR_HIGH - PWR_S5_REAR_LOW;
+			new_state |= THROT_TYPE_A_REAR;
+		}
+		/*
+		 * [2] If type A front not already throttled, and power still
+		 * needed, limit type A front.
+		 */
+		if (!(new_state & THROT_TYPE_A_FRONT) && headroom_5v_s5 < 0) {
+			headroom_5v_s5 += PWR_S5_FRONT_HIGH - PWR_S5_FRONT_LOW;
+			new_state |= THROT_TYPE_A_FRONT;
+		}
+	}
+	/*
+	 * Turn the throttles on or off if they have changed.
+	 */
+	diff = new_state ^ current_state;
+	current_state = new_state;
+	if (diff & THROT_PROCHOT) {
+		int prochot = (new_state & THROT_PROCHOT) ? 0 : 1;
+
+		gpio_set_level(GPIO_EC_PROCHOT_ODL, prochot);
+	}
+	if (diff & THROT_TYPE_C0) {
+		enum tcpc_rp_value rp = (new_state & THROT_TYPE_C0)
+			? TYPEC_RP_1A5 : TYPEC_RP_3A0;
+
+		ppc_set_vbus_source_current_limit(0, rp);
+		tcpm_select_rp_value(0, rp);
+		pd_update_contract(0);
+	}
+	if (diff & THROT_TYPE_C1) {
+		enum tcpc_rp_value rp = (new_state & THROT_TYPE_C1)
+			? TYPEC_RP_1A5 : TYPEC_RP_3A0;
+
+		ppc_set_vbus_source_current_limit(1, rp);
+		tcpm_select_rp_value(1, rp);
+		pd_update_contract(1);
+	}
+	if (diff & THROT_TYPE_C2) {
+		enum tcpc_rp_value rp = (new_state & THROT_TYPE_C2)
+			? TYPEC_RP_1A5 : TYPEC_RP_3A0;
+
+		ppc_set_vbus_source_current_limit(2, rp);
+		tcpm_select_rp_value(2, rp);
+		pd_update_contract(2);
+	}
+	if (diff & THROT_TYPE_A_REAR) {
+		int typea_bc = (new_state & THROT_TYPE_A_REAR) ? 1 : 0;
+
+		gpio_set_level(GPIO_USB_A_LOW_PWR0_OD, typea_bc);
+		gpio_set_level(GPIO_USB_A_LOW_PWR1_OD, typea_bc);
+	}
+	if (diff & THROT_TYPE_A_FRONT) {
+		int typea_bc = (new_state & THROT_TYPE_A_FRONT) ? 1 : 0;
+
+		gpio_set_level(GPIO_USB_A_LOW_PWR2_OD, typea_bc);
+		gpio_set_level(GPIO_USB_A_LOW_PWR3_OD, typea_bc);
+	}
+	hook_call_deferred(&power_monitor_data, delay);
+}
diff --git a/board/brask/board.h b/board/brask/board.h
index a9bb47c3b0..ca794a6eb2 100644
--- a/board/brask/board.h
+++ b/board/brask/board.h
@@ -165,6 +165,7 @@ enum adc_channel {
 	ADC_TEMP_SENSOR_3_WIFI,
 	ADC_TEMP_SENSOR_4_DIMM,
 	ADC_VBUS,
+	ADC_PPVAR_IMON,              /* ADC3 */
 	ADC_CH_COUNT
 };
 
diff --git a/board/brask/gpio.inc b/board/brask/gpio.inc
index fddf0ee837..90beebe51e 100644
--- a/board/brask/gpio.inc
+++ b/board/brask/gpio.inc
@@ -6,6 +6,7 @@
  */
 
 /* INTERRUPT GPIOs: */
+
 GPIO_INT(ACOK_OD,                    PIN(0, 0), GPIO_INT_BOTH, extpower_interrupt)
 GPIO_INT(EC_PROCHOT_IN_L,            PIN(F, 0), GPIO_INT_BOTH, throttle_ap_prochot_input_interrupt)
 GPIO_INT(EC_WP_ODL,                  PIN(A, 1), GPIO_INT_BOTH, switch_interrupt)
@@ -28,6 +29,11 @@ GPIO_INT(USB_C2_PPC_INT_ODL,         PIN(7, 0), GPIO_INT_FALLING, ppc_interrupt)
 GPIO_INT(USB_C2_RT_INT_ODL,          PIN(4, 1), GPIO_INT_FALLING, retimer_interrupt)
 GPIO_INT(BJ_ADP_PRESENT_ODL,         PIN(8, 2), GPIO_INT_BOTH | GPIO_PULL_UP, adp_connect_interrupt)
 GPIO_INT(EC_RECOVERY_BTN_OD,         PIN(2, 3), GPIO_INT_BOTH, button_interrupt)
+GPIO_INT(HDMI_CONN_OC_ODL,           PIN(2, 4), GPIO_INPUT | GPIO_INT_BOTH, port_ocp_interrupt)
+GPIO_INT(USB_A0_OC_ODL,              PIN(3, 1), GPIO_INPUT | GPIO_PULL_UP | GPIO_INT_BOTH, port_ocp_interrupt)
+GPIO_INT(USB_A1_OC_ODL,              PIN(3, 0), GPIO_INPUT | GPIO_PULL_UP | GPIO_INT_BOTH, port_ocp_interrupt)
+GPIO_INT(USB_A2_OC_ODL,              PIN(2, 7), GPIO_INPUT | GPIO_PULL_UP | GPIO_INT_BOTH, port_ocp_interrupt)
+GPIO_INT(USB_A3_OC_ODL,              PIN(2, 6), GPIO_INPUT | GPIO_PULL_UP | GPIO_INT_BOTH, port_ocp_interrupt)
 
 /* CCD */
 GPIO(CCD_MODE_ODL,                   PIN(E, 5), GPIO_INPUT)
@@ -44,7 +50,7 @@ GPIO(ANALOG_PPVAR_PWR_IN_IMON_EC,    PIN(4, 2), GPIO_INPUT)
 
 /* Display */
 GPIO(DP_CONN_OC_ODL,                 PIN(2, 5), GPIO_INPUT)
-GPIO(HDMI_CONN_OC_ODL,               PIN(2, 4), GPIO_INPUT)
+
 
 /* BarrelJack */
 GPIO(EN_PPVAR_BJ_ADP_L,              PIN(0, 7), GPIO_OUT_LOW)
@@ -107,10 +113,6 @@ GPIO(EC_I2C_USB_C1_TCPC_SDA,         PIN(F, 2), GPIO_INPUT)
 
 /* USBA */
 GPIO(EN_PP5000_USBA,                 PIN(D, 7), GPIO_OUT_LOW)
-GPIO(USB_A0_OC_ODL,                  PIN(3, 1), GPIO_INPUT | GPIO_PULL_UP)
-GPIO(USB_A1_OC_ODL,                  PIN(3, 0), GPIO_INPUT | GPIO_PULL_UP)
-GPIO(USB_A2_OC_ODL,                  PIN(2, 7), GPIO_INPUT | GPIO_PULL_UP)
-GPIO(USB_A3_OC_ODL,                  PIN(2, 6), GPIO_INPUT | GPIO_PULL_UP)
 GPIO(USB_A0_STATUS_L,                PIN(2, 1), GPIO_INPUT)
 GPIO(USB_A1_STATUS_L,                PIN(2, 0), GPIO_INPUT)
 GPIO(USB_A2_STATUS_L,                PIN(1, 7), GPIO_INPUT)
@@ -179,4 +181,4 @@ UNUSED(PIN(8, 6))       /* GPIO86/TXD/CR_SOUT2 */
 UNUSED(PIN(1, 3))       /* KSO06/GPO13/GP_SEL# */
 UNUSED(PIN(1, 2))       /* KSO07/GPO12/JEN# */
 UNUSED(PIN(0, 6))       /* KSO11/GPIO06/P80_CLK */
-UNUSED(PIN(0, 4))       /* KSO13/GPIO04 */
\ No newline at end of file
+UNUSED(PIN(0, 4))       /* KSO13/GPIO04 */
diff --git a/board/brask/led.c b/board/brask/led.c
index 6aaa890ec8..68dffb67a7 100644
--- a/board/brask/led.c
+++ b/board/brask/led.c
@@ -250,3 +250,12 @@ int led_set_brightness(enum ec_led_id id, const uint8_t *brightness)
 	else
 		return set_color(id, LED_OFF, 0);
 }
+void board_set_charge_limit(int port, int supplier, int charge_ma,
+				int max_ma, int charge_mv)
+{
+  /* Blink alert if insufficient power per system_can_boot_ap(). */
+	int insufficient_power =
+		(charge_ma * charge_mv) <
+		(CONFIG_CHARGER_MIN_POWER_MW_FOR_POWER_ON * 1000);
+	led_alert(insufficient_power);
+}
diff --git a/board/brask/sensors.c b/board/brask/sensors.c
index 7071c89f54..2803dd1025 100644
--- a/board/brask/sensors.c
+++ b/board/brask/sensors.c
@@ -46,6 +46,13 @@ const struct adc_t adc_channels[] = {
 		.factor_mul = ADC_MAX_VOLT * 39,
 		.factor_div = (ADC_READ_MAX + 1) * 5,
 	},
+	[ADC_PPVAR_IMON] = {  /* 872.3 mV/A */
+		.name = "PPVAR_IMON",
+		.input_ch = NPCX_ADC_CH3,
+		.factor_mul = ADC_MAX_VOLT * 1433,
+		.factor_div = (ADC_READ_MAX + 1) * 1250,
+	},
+
 };
 BUILD_ASSERT(ARRAY_SIZE(adc_channels) == ADC_CH_COUNT);