From a39605248760a1acdb6850ef9e7f289bee7cb6fd Mon Sep 17 00:00:00 2001
From: Markus Koch <markus@notsyncing.net>
Date: Fri, 31 Jul 2020 18:23:58 +0200
Subject: [PATCH] fw: Implement power-on battery check

---
 firmware/batmon.c | 25 +++++++++++++++++++++++++
 firmware/batmon.h |  1 +
 firmware/main.c   |  1 +
 firmware/pm.c     |  6 +++++-
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/firmware/batmon.c b/firmware/batmon.c
index c70e9ca..f1a150f 100644
--- a/firmware/batmon.c
+++ b/firmware/batmon.c
@@ -49,3 +49,28 @@ inline uint8_t batmon_get_voltage()
 {
 	return vbat;
 }
+
+static uint8_t batmon_get_voltage_sync()
+{
+	uint16_t sum = 0;
+	uint8_t cnt = 255;
+
+	ADCSRA |= (1 << ADSC);
+
+	do {
+		if (ADCSRA & (1 << ADIF)) {
+			sum += ADCH;
+			ADCSRA &= ~(1 << ADIF);
+			ADCSRA |= (1 << ADSC);
+			cnt--;
+		}
+	} while (cnt);
+
+	return (sum >> 8);
+}
+
+// Note: Call batmon_init() after using this function before using batmon_proc() again
+inline uint8_t batmon_ok_to_boot()
+{
+	return (batmon_get_voltage_sync() > BAT_THRES_POWER_ON);
+}
diff --git a/firmware/batmon.h b/firmware/batmon.h
index fd5976f..7acc2b5 100644
--- a/firmware/batmon.h
+++ b/firmware/batmon.h
@@ -12,5 +12,6 @@
 void batmon_init();
 uint8_t batmon_get_voltage();
 uint8_t batmon_proc();
+uint8_t batmon_ok_to_boot();
 
 #endif // BATMON_H
diff --git a/firmware/main.c b/firmware/main.c
index 8c94a35..afafecd 100644
--- a/firmware/main.c
+++ b/firmware/main.c
@@ -88,6 +88,7 @@ int main()
 	MCUSR &= ~(1 << WDRF);
 	WDTCSR = (1 << WDCE);
 	cli();
+	_delay_ms(25);
 
 	suspend();
 
diff --git a/firmware/pm.c b/firmware/pm.c
index c81a535..dc4af6f 100644
--- a/firmware/pm.c
+++ b/firmware/pm.c
@@ -4,6 +4,7 @@
 #include <avr/interrupt.h>
 #include <avr/pgmspace.h>
 #include "pm.h"
+#include "batmon.h"
 
 static void disable_periphery()
 {
@@ -58,7 +59,10 @@ void reset()
 
 char* post()
 {
-	// TODO: Implement battery voltage check
 	_delay_ms(500);
+
+	if (!batmon_ok_to_boot())
+		return PSTR("Low battery.");
+
 	return 0;
 }