zinger: fast over-current protection

When the supply output is enabled, ensure that we detect quickly any
over-current situation by setting an analog watchdog in continuous
conversion mode.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BRANCH=none
BUG=chrome-os-partner:28331
TEST=plug an electronic load to Zinger and see the OCP triggered
quickly when we go above the current threshold.

Change-Id: I7da50ef242addbd2f4f48f624494daa321ac22b2
Reviewed-on: https://chromium-review.googlesource.com/199924
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Alec Berg <alecaberg@chromium.org>

2 files changed, 67 insertions, 2 deletions

diff --git a/board/zinger/hardware.c b/board/zinger/hardware.c
index cf71c3ffad..0bafa48839 100644
--- a/board/zinger/hardware.c
+++ b/board/zinger/hardware.c
@@ -116,6 +116,10 @@ static void adc_init(void)
 	STM32_ADC_CFGR2 = 0;
 	/* Sampling time : 13.5 ADC clock cycles. */
 	STM32_ADC_SMPR = 2;
+	/* Disable interrupts */
+	STM32_ADC_IER = 0;
+	/* Analog watchdog IRQ */
+	task_enable_irq(STM32_IRQ_ADC_COMP);
 }
 
 static void uart_init(void)
@@ -171,7 +175,7 @@ int adc_read_channel(enum adc_channel ch)
 	/* Select channel to convert */
 	STM32_ADC_CHSELR = 1 << ch;
 	/* Clear flags */
-	STM32_ADC_ISR = 0xe;
+	STM32_ADC_ISR = 0x8e;
 	/* Start conversion */
 	STM32_ADC_CR |= 1 << 2; /* ADSTART */
 	/* Wait for end of conversion */
@@ -183,6 +187,40 @@ int adc_read_channel(enum adc_channel ch)
 	return value;
 }
 
+int adc_enable_watchdog(int ch, int high, int low)
+{
+	/* Set thresholds */
+	STM32_ADC_TR = ((high & 0xfff) << 16) | (low & 0xfff);
+	/* Select channel to convert */
+	STM32_ADC_CHSELR = 1 << ch;
+	/* Clear flags */
+	STM32_ADC_ISR = 0x8e;
+	/* Set Watchdog enable bit on a single channel / continuous mode */
+	STM32_ADC_CFGR1 = (ch << 26) | (1 << 23) | (1 << 22)
+			|  (1 << 13) | (1 << 12);
+	/* Enable watchdog interrupt */
+	STM32_ADC_IER = 1 << 7;
+	/* Start continuous conversion */
+	STM32_ADC_CR |= 1 << 2; /* ADSTART */
+
+	return EC_SUCCESS;
+}
+
+int adc_disable_watchdog(void)
+{
+	/* Stop on-going conversion */
+	STM32_ADC_CR |= 1 << 4; /* ADSTP */
+	/* Wait for conversion to stop */
+	while (STM32_ADC_CR & (1 << 4))
+		;
+	/* CONT=0 -> continuous mode off / Clear Watchdog enable */
+	STM32_ADC_CFGR1 = 1 << 12;
+	/* Disable interrupt */
+	STM32_ADC_IER = 0;
+
+	return EC_SUCCESS;
+}
+
 /* ---- flash handling ---- */
 
 /*
diff --git a/board/zinger/usb_pd_policy.c b/board/zinger/usb_pd_policy.c
index c55f33561c..a23328bc3a 100644
--- a/board/zinger/usb_pd_policy.c
+++ b/board/zinger/usb_pd_policy.c
@@ -9,6 +9,7 @@
 #include "console.h"
 #include "debug.h"
 #include "hooks.h"
+#include "irq_handler.h"
 #include "registers.h"
 #include "sha1.h"
 #include "timer.h"
@@ -59,6 +60,7 @@ static inline int output_is_enabled(void)
 enum faults {
 	FAULT_OK = 0,
 	FAULT_OCP, /* Over-Current Protection */
+	FAULT_FAST_OCP, /* Over-Current Protection for interrupt context */
 	FAULT_OVP, /* Under or Over-Voltage Protection */
 };
 
@@ -161,6 +163,9 @@ int pd_set_power_supply_ready(void)
 		return EC_ERROR_INVAL;
 
 	output_enable();
+	/* Over-current monitoring */
+	adc_enable_watchdog(ADC_CH_A_SENSE, MAX_CURRENT, 0);
+
 	return EC_SUCCESS; /* we are ready */
 }
 
@@ -171,16 +176,28 @@ void pd_power_supply_reset(void)
 	volt_idx = 0;
 	set_output_voltage(VO_5V);
 	/* TODO transition delay */
+
+	/* Stop OCP monitoring to save power */
+	adc_disable_watchdog();
 }
 
 int pd_board_checks(void)
 {
 	int vbus_volt, vbus_amp;
+	int watchdog_enabled = STM32_ADC_CFGR1 & (1 << 23);
+
+	if (watchdog_enabled)
+		/* if the watchdog is enabled, stop it to do other readings */
+		adc_disable_watchdog();
 
 	vbus_volt = adc_read_channel(ADC_CH_V_SENSE);
 	vbus_amp = adc_read_channel(ADC_CH_A_SENSE);
 
-	if (vbus_amp > MAX_CURRENT) {
+	if (watchdog_enabled)
+		/* re-enable fast OCP */
+		adc_enable_watchdog(ADC_CH_A_SENSE, MAX_CURRENT, 0);
+
+	if ((fault == FAULT_FAST_OCP) || (vbus_amp > MAX_CURRENT)) {
 		debug_printf("OverCurrent : %d mA\n",
 		  vbus_amp * VDDA_MV / CURR_GAIN * 1000 / R_SENSE / ADC_SCALE);
 		fault = FAULT_OCP;
@@ -208,6 +225,16 @@ int pd_board_checks(void)
 
 }
 
+void IRQ_HANDLER(STM32_IRQ_ADC_COMP)(void)
+{
+	/* cut the power output */
+	pd_power_supply_reset();
+	/* Clear flags */
+	STM32_ADC_ISR = 0x8e;
+	/* record a special fault, the normal check will record the timeout */
+	fault = FAULT_FAST_OCP;
+}
+
 /* ----------------- Vendor Defined Messages ------------------ */
 int pd_custom_vdm(void *ctxt, int cnt, uint32_t *payload, uint32_t **rpayload)
 {