altos/telefire*: Do voltage tests in decivolts instead of ADC units

This requires that each pad device specify the ADC reference voltage
and all relevant voltage divider resistor values explicitly so that
the ADC values can be converted to decivolts and compared with one
another. This should be easier to understand in the future when
reading the code.

Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 69 insertions, 59 deletions

diff --git a/src/drivers/ao_pad.c b/src/drivers/ao_pad.c
index b0ec2161..ed749d1c 100644
--- a/src/drivers/ao_pad.c
+++ b/src/drivers/ao_pad.c
@@ -153,13 +153,36 @@ ao_pad_run(void)
 
 #define AO_PAD_ARM_SIREN_INTERVAL	200
 
-#ifndef AO_PYRO_R_PYRO_SENSE
-#define AO_PYRO_R_PYRO_SENSE	100
-#define AO_PYRO_R_SENSE_GND	27
-#define AO_FIRE_R_POWER_FET	100
-#define AO_FIRE_R_FET_SENSE	100
-#define AO_FIRE_R_SENSE_GND	27
-#endif
+/* Resistor values needed for various voltage test ratios:
+ *
+ *	Net names involved:
+ *
+ *	V_BATT		Battery power, after the initial power switch
+ *	V_PYRO		Pyro power, after the pyro power switch (and initial power switch)
+ *	PYRO_SENSE	ADC input to sense V_PYRO voltage
+ *	BATT_SENSE	ADC input to sense V_BATT voltage
+ *	IGNITER		FET output to pad (the other pad lead hooks to V_PYRO)
+ *	IGNITER_SENSE	ADC input to sense igniter voltage
+ *
+ *	AO_PAD_R_V_BATT_BATT_SENSE	Resistor from battery rail to battery sense input
+ *	AO_PAD_R_BATT_SENSE_GND		Resistor from battery sense input to ground
+ *
+ *	AO_PAD_R_V_BATT_V_PYRO		Resistor from battery rail to pyro rail
+ *	AO_PAD_R_V_PYRO_PYRO_SENSE	Resistor from pyro rail to pyro sense input
+ *	AO_PAD_R_PYRO_SENSE_GND		Resistor from pyro sense input to ground
+ *
+ *	AO_PAD_R_V_PYRO_IGNITER		Optional resistors from pyro rail to FET igniter output
+ *	AO_PAD_R_IGNITER_IGNITER_SENSE	Resistors from FET igniter output to igniter sense ADC inputs
+ *	AO_PAD_R_IGNITER_SENSE_GND	Resistors from igniter sense ADC inputs to ground
+ */
+
+int16_t
+ao_pad_decivolt(int16_t adc, int16_t r_plus, int16_t r_minus)
+{
+	int32_t	mul = (int32_t) AO_ADC_REFERENCE_DV * (r_plus + r_minus);
+	int32_t div = (int32_t) AO_ADC_MAX * r_minus;
+	return ((int32_t) adc * mul + mul/2) / div;
+}
 
 static void
 ao_pad_monitor(void)
@@ -174,6 +197,7 @@ ao_pad_monitor(void)
 	sample = ao_data_head;
 	for (;;) {
 		__pdata int16_t			pyro;
+
 		ao_arch_critical(
 			while (sample == ao_data_head)
 				ao_sleep((void *) DATA_TO_XDATA(&ao_data_head));
@@ -183,28 +207,18 @@ ao_pad_monitor(void)
 		packet = &ao_data_ring[sample];
 		sample = ao_data_ring_next(sample);
 
-		pyro = packet->adc.pyro;
+		/* Reply battery voltage */
+		query.battery = ao_pad_decivolt(packet->adc.batt, AO_PAD_R_V_BATT_BATT_SENSE, AO_PAD_R_BATT_SENSE_GND);
 
-#define VOLTS_TO_PYRO(x) ((int16_t) ((x) * ((1.0 * AO_PYRO_R_SENSE_GND) / \
-					    (1.0 * (AO_PYRO_R_SENSE_GND + AO_PYRO_R_PYRO_SENSE)) / 3.3 * AO_ADC_MAX)))
+		/* Current pyro voltage */
+		pyro = ao_pad_decivolt(packet->adc.pyro,
+				       AO_PAD_R_V_PYRO_PYRO_SENSE,
+				       AO_PAD_R_PYRO_SENSE_GND);
 
-
-#define VOLTS_TO_FIRE(x) ((int16_t) ((x) * ((1.0 * AO_FIRE_R_SENSE_GND) / \
-					    (1.0 * (AO_FIRE_R_SENSE_GND + AO_FIRE_R_FET_SENSE)) / 3.3 * AO_ADC_MAX)))
-
-		/* convert ADC value to voltage in tenths, then add .2 for the diode drop */
-		query.battery = (packet->adc.batt + 96) / 192 + 2;
 		cur = 0;
-		if (pyro > VOLTS_TO_PYRO(10)) {
+		if (pyro > query.battery * 7 / 8) {
 			query.arm_status = AO_PAD_ARM_STATUS_ARMED;
 			cur |= AO_LED_ARMED;
-#if AO_FIRE_R_POWER_FET
-		} else if (pyro > VOLTS_TO_PYRO(5)) {
-			if ((ao_time() % 100) < 50)
-				cur |= AO_LED_ARMED;
-			query.arm_status = AO_PAD_ARM_STATUS_UNKNOWN;
-			arm_beep_time = 0;
-#endif
 		} else {
 			query.arm_status = AO_PAD_ARM_STATUS_DISARMED;
 			arm_beep_time = 0;
@@ -217,54 +231,50 @@ ao_pad_monitor(void)
 			cur |= AO_LED_GREEN;
 
 		for (c = 0; c < AO_PAD_NUM; c++) {
-			int16_t		sense = packet->adc.sense[c];
+			int16_t		sense = ao_pad_decivolt(packet->adc.sense[c],
+								AO_PAD_R_IGNITER_IGNITER_SENSE,
+								AO_PAD_R_IGNITER_SENSE_GND);
 			uint8_t	status = AO_PAD_IGNITER_STATUS_UNKNOWN;
 
 			/*
-			 *	pyro is run through a divider, so pyro = v_pyro * 27 / 127 ~= v_pyro / 20
-			 *	v_pyro = pyro * 127 / 27
-			 *
-			 *		v_pyro \
-			 *	100k		igniter
-			 *		output /
-			 *	100k           \
-			 *		sense   relay
-			 *	27k            /
-			 *		gnd ---
+			 *	Here's the resistor stack on each
+			 *	igniter channel. Note that
+			 *	AO_PAD_R_V_PYRO_IGNITER is optional
 			 *
-			 *		v_pyro \
-			 *	200k		igniter
-			 *		output /
-			 *	200k           \
-			 *		sense   relay
-			 *	22k            /
-			 *		gnd ---
+			 *					v_pyro \
+			 *	AO_PAD_R_V_PYRO_IGNITER			igniter
+			 *					output /
+			 *	AO_PAD_R_IGNITER_IGNITER_SENSE         \
+			 *					sense   relay
+			 *	AO_PAD_R_IGNITER_SENSE_GND	       /
+			 *					gnd ---
 			 *
-			 *	If the relay is closed, then sense will be 0
-			 *	If no igniter is present, then sense will be v_pyro * 27k/227k = pyro * 127 / 227 ~= pyro/2
-			 *	If igniter is present, then sense will be v_pyro * 27k/127k ~= v_pyro / 20 = pyro
 			 */
 
-#if AO_FIRE_R_POWER_FET
+#ifdef AO_PAD_R_V_PYRO_IGNITER
 			if (sense <= pyro / 8) {
+				/* close to zero → relay is closed */
 				status = AO_PAD_IGNITER_STATUS_NO_IGNITER_RELAY_CLOSED;
 				if ((ao_time() % 100) < 50)
 					cur |= AO_LED_CONTINUITY(c);
-			} else
-			if (pyro / 8 * 3 <= sense && sense <= pyro / 8 * 5)
-				status = AO_PAD_IGNITER_STATUS_NO_IGNITER_RELAY_OPEN;
-			else if (pyro / 8 * 7 <= sense) {
-				status = AO_PAD_IGNITER_STATUS_GOOD_IGNITER_RELAY_OPEN;
-				cur |= AO_LED_CONTINUITY(c);
-			}
-#else
-			if (sense >= pyro / 8 * 5) {
-				status = AO_PAD_IGNITER_STATUS_GOOD_IGNITER_RELAY_OPEN;
-				cur |= AO_LED_CONTINUITY(c);
-			} else {
-				status = AO_PAD_IGNITER_STATUS_NO_IGNITER_RELAY_OPEN;
 			}
+			else
 #endif
+			{
+				if (sense >= (pyro * 7) / 8) {
+
+					/* sense close to pyro voltage; igniter is good
+					 */
+					status = AO_PAD_IGNITER_STATUS_GOOD_IGNITER_RELAY_OPEN;
+					cur |= AO_LED_CONTINUITY(c);
+				} else {
+
+					/* relay not shorted (if we can tell),
+					 * and igniter not obviously present
+					 */
+					status = AO_PAD_IGNITER_STATUS_NO_IGNITER_RELAY_OPEN;
+				}
+			}
 			query.igniter_status[c] = status;
 		}
 		if (cur != prev) {