temp_sensor: Separate ADC interface and thermistor maths

Separate the bd99992gw ADC interface from the NCP15WB thermistor
adc-to-temp maths so that the thermistor can be used with various
other interfaces.

BUG=chrome-os-partner:44764
TEST=make buildall -j
Manual on Glados. Boot to S0, run "temps".
Verify that temperatures start around 28C and begin to increase after
system is powered-on for a long duration.
BRANCH=None

Change-Id: I3e72e9f390feebaac2440dbe722485f8d1cf8c56
Signed-off-by: Wonjoon Lee <woojoo.lee@samsung.com>
Reviewed-on: https://chromium-review.googlesource.com/296871
Reviewed-by: Shawn N <shawnn@chromium.org>

3 files changed, 128 insertions, 88 deletions

diff --git a/driver/temp_sensor/bd99992gw.c b/driver/temp_sensor/bd99992gw.c
index b46d8512fe..f2a48eb2d5 100644
--- a/driver/temp_sensor/bd99992gw.c
+++ b/driver/temp_sensor/bd99992gw.c
@@ -17,6 +17,7 @@
 #include "hooks.h"
 #include "i2c.h"
 #include "temp_sensor.h"
+#include "thermistor.h"
 #include "timer.h"
 #include "util.h"
 
@@ -35,46 +36,6 @@ static enum bd99992gw_adc_channel
  */
 #define ADC_LOOP_PERIOD BD99992GW_ADC1CNTL1_SLP27MS
 
-/*
- * ADC-to-temp conversion assumes recommended thermistor / resistor
- * configuration specified in datasheet (NCP15WB* / 24.9K).
- * For 50C through 100C, use linear interpolation from discreet points
- * in table below. For temps < 50C, use a simplified linear function.
- */
-#define ADC_DISCREET_RANGE_START_TEMP	50
-/* 10 bit ADC result corresponding to START_TEMP */
-#define ADC_DISCREET_RANGE_START_RESULT	407
-
-#define ADC_DISCREET_RANGE_LIMIT_TEMP	100
-/* 10 bit ADC result corresponding to LIMIT_TEMP */
-#define ADC_DISCREET_RANGE_LIMIT_RESULT	107
-
-/* Table entries in steppings of 5C */
-#define ADC_DISCREET_RANGE_STEP		5
-
-/* Discreet range ADC results (9 bit) per temperature, in 5 degree steps */
-static const uint8_t adc_result[] = {
-	203,	/* 50 C */
-	178,	/* 55 C */
-	157,	/* 60 C */
-	138,	/* 65 C */
-	121,	/* 70 C */
-	106,	/* 75 C */
-	93,	/* 80 C */
-	81,	/* 85 C */
-	70,	/* 90 C */
-	61,	/* 95 C */
-	53,	/* 100 C */
-};
-
-/*
- * From 20C (reasonable lower limit of temperatures we care about accuracy)
- * to 50C, the temperature curve is roughly linear, so we don't need to include
- * data points in our table.
- */
-#define adc_to_temp(result) (ADC_DISCREET_RANGE_START_TEMP - \
-	(((result) - ADC_DISCREET_RANGE_START_RESULT) * 3 + 16) / 32)
-
 static int raw_read8(const int offset, int *data_ptr)
 {
 	int ret;
@@ -143,55 +104,14 @@ DECLARE_HOOK(HOOK_INIT, bd99992gw_init, HOOK_PRIO_DEFAULT);
 DECLARE_HOOK(HOOK_CHIPSET_RESUME, bd99992gw_init, HOOK_PRIO_DEFAULT);
 
 /* Convert ADC result to temperature in celsius */
-test_export_static int bd99992gw_get_temp(uint16_t adc)
+static int bd99992gw_get_temp(uint16_t adc)
 {
-	int temp;
-	int head, tail, mid;
-	uint8_t delta, step;
-
-	/* Is ADC result in linear range? */
-	if (adc >= ADC_DISCREET_RANGE_START_RESULT) {
-		temp = adc_to_temp(adc);
-	}
-	/* Hotter than our discreet range limit? */
-	else if (adc <= ADC_DISCREET_RANGE_LIMIT_RESULT) {
-		temp = ADC_DISCREET_RANGE_LIMIT_TEMP;
-	}
-	/* We're in the discreet range */
-	else {
-		/* Table uses 9 bit ADC values */
-		adc /= 2;
-
-		/* Binary search to find proper table entry */
-		head = 0;
-		tail = ARRAY_SIZE(adc_result) - 1;
-		while (head != tail) {
-			mid = (head + tail) / 2;
-			if (adc_result[mid] >= adc &&
-			    adc_result[mid+1] < adc)
-				break;
-			if (adc_result[mid] > adc)
-				head = mid + 1;
-			else
-				tail = mid;
-		}
-
-		/* Now fit between table entries using linear interpolation. */
-		if (head != tail) {
-			delta = adc_result[mid] - adc_result[mid + 1];
-			step = ((adc_result[mid] - adc) *
-				ADC_DISCREET_RANGE_STEP + delta / 2) / delta;
-		} else {
-			/* Edge case where adc = max */
-			mid = head;
-			step = 0;
-		}
-
-		temp = ADC_DISCREET_RANGE_START_TEMP +
-		       ADC_DISCREET_RANGE_STEP * mid + step;
-	}
-
-	return temp;
+#ifdef CONFIG_THERMISTOR_NCP15WB
+	return ncp15wb_calculate_temp(adc);
+#else
+#error "Unknown thermistor for bd99992gw"
+	return 0;
+#endif
 }
 
 /* Get temperature from requested sensor */
diff --git a/driver/temp_sensor/thermistor.h b/driver/temp_sensor/thermistor.h
new file mode 100644
index 0000000000..3bb5335ddd
--- /dev/null
+++ b/driver/temp_sensor/thermistor.h
@@ -0,0 +1,20 @@
+/* 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.
+ */
+
+/* Thermistor module for Chrome EC */
+
+#ifndef __CROS_EC_TEMP_SENSOR_THERMISTOR_H
+#define __CROS_EC_TEMP_SENSOR_THERMISTOR_H
+
+/**
+ * ncp15wb temperature conversion routine.
+ *
+ * @param adc	10bit raw data on adc.
+ *
+ * @return	temperature in C.
+ */
+int ncp15wb_calculate_temp(uint16_t adc);
+
+#endif  /* __CROS_EC_TEMP_SENSOR_THERMISTOR_NCP15WB_H */
diff --git a/driver/temp_sensor/thermistor_ncp15wb.c b/driver/temp_sensor/thermistor_ncp15wb.c
new file mode 100644
index 0000000000..51e884ed35
--- /dev/null
+++ b/driver/temp_sensor/thermistor_ncp15wb.c
@@ -0,0 +1,100 @@
+/* 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.
+ */
+
+/* NCP15WB thermistor module for Chrome EC */
+
+#include "common.h"
+#include "thermistor.h"
+#include "util.h"
+
+/*
+ * ADC-to-temp conversion assumes recommended thermistor / resistor
+ * configuration (NCP15WB* / 24.9K) with a 10-bit ADC.
+ * For 50C through 100C, use linear interpolation from discreet points
+ * in table below. For temps < 50C, use a simplified linear function.
+ */
+#define ADC_DISCREET_RANGE_START_TEMP	50
+/* 10 bit ADC result corresponding to START_TEMP */
+#define ADC_DISCREET_RANGE_START_RESULT	407
+
+#define ADC_DISCREET_RANGE_LIMIT_TEMP	100
+/* 10 bit ADC result corresponding to LIMIT_TEMP */
+#define ADC_DISCREET_RANGE_LIMIT_RESULT	107
+
+/* Table entries in steppings of 5C */
+#define ADC_DISCREET_RANGE_STEP		5
+
+/* Discreet range ADC results (9 bit) per temperature, in 5 degree steps */
+static const uint8_t adc_result[] = {
+	203,	/* 50 C */
+	178,	/* 55 C */
+	157,	/* 60 C */
+	138,	/* 65 C */
+	121,	/* 70 C */
+	106,	/* 75 C */
+	93,	/* 80 C */
+	81,	/* 85 C */
+	70,	/* 90 C */
+	61,	/* 95 C */
+	53,	/* 100 C */
+};
+
+/*
+ * From 20C (reasonable lower limit of temperatures we care about accuracy)
+ * to 50C, the temperature curve is roughly linear, so we don't need to include
+ * data points in our table.
+ */
+#define adc_to_temp(result) (ADC_DISCREET_RANGE_START_TEMP - \
+	(((result) - ADC_DISCREET_RANGE_START_RESULT) * 3 + 16) / 32)
+
+/* Convert ADC result (10 bit) to temperature in celsius */
+int ncp15wb_calculate_temp(uint16_t adc)
+{
+	int temp;
+	int head, tail, mid;
+	uint8_t delta, step;
+
+	/* Is ADC result in linear range? */
+	if (adc >= ADC_DISCREET_RANGE_START_RESULT)
+		temp = adc_to_temp(adc);
+	/* Hotter than our discreet range limit? */
+	else if (adc <= ADC_DISCREET_RANGE_LIMIT_RESULT)
+		temp = ADC_DISCREET_RANGE_LIMIT_TEMP;
+	/* We're in the discreet range */
+	else {
+		/* Table uses 9 bit ADC values */
+		adc /= 2;
+
+		/* Binary search to find proper table entry */
+		head = 0;
+		tail = ARRAY_SIZE(adc_result) - 1;
+		while (head != tail) {
+			mid = (head + tail) / 2;
+			if (adc_result[mid] >= adc &&
+			    adc_result[mid+1] < adc)
+				break;
+			if (adc_result[mid] > adc)
+				head = mid + 1;
+			else
+				tail = mid;
+		}
+
+		/* Now fit between table entries using linear interpolation. */
+		if (head != tail) {
+			delta = adc_result[mid] - adc_result[mid + 1];
+			step = ((adc_result[mid] - adc) *
+				ADC_DISCREET_RANGE_STEP + delta / 2) / delta;
+		} else {
+			/* Edge case where adc = max */
+			mid = head;
+			step = 0;
+		}
+
+		temp = ADC_DISCREET_RANGE_START_TEMP +
+		       ADC_DISCREET_RANGE_STEP * mid + step;
+	}
+
+	return temp;
+}