From ea6bafc1320bec14e79b97aad8f072146a11583c Mon Sep 17 00:00:00 2001
From: William Harrington <kb0iic@berzerkula.org>
Date: Wed, 31 Jul 2019 21:39:03 -0500
Subject: Add a function for determining day of week from calendar date and
 rename dayofweek to day like in datasheet.

---
 ds3231.c | 10 +++++++---
 ds3231.h |  3 ++-
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/ds3231.c b/ds3231.c
index c7cd797..b70a09b 100755
--- a/ds3231.c
+++ b/ds3231.c
@@ -24,6 +24,10 @@ int DEC_2_BCD(int to_convert) {
     return ((to_convert / 10) << 4) + (to_convert % 10);
 }
 
+unsigned int Get_DayOfWeek(unsigned int y, unsigned int m,  unsigned int d) {
+    return (d += m < 3 ? y-- : y - 2, 23*m/9 + d + 4 + y/4- y/100 + y/400)%7 + 1; // 01 - 07, 01 = Sunday
+}
+
 void Read_Alarms_Temp() {
     I2C_Master_Start(); // Start I2C
     I2C_Master_Write(0xD0); // RTC chip address
@@ -59,11 +63,11 @@ void Set_Date() {
     I2C_Master_Stop();
 }
 
-void Set_DayOfWeek() {
+void Set_DayOfWeek(int dow) {
     I2C_Master_Start(); // Start I2C
     I2C_Master_Write(0xD0); // RTC Chip address
     I2C_Master_Write(3); // send register address
-    I2C_Master_Write(dayOfWeek); //update day of week
+    I2C_Master_Write(dow); //update day of week
     I2C_Master_Stop();
 }
 
@@ -89,7 +93,7 @@ void Update_Current_Date_Time() {
     sec = BCD_2_DEC(I2C_Master_Read(1)); // Read sec from register 00h
     min = BCD_2_DEC(I2C_Master_Read(1)); // Read min from register 01h
     hour = BCD_2_DEC(I2C_Master_Read(1)); // Read hour from register 02h
-    weekday = I2C_Master_Read(1); // Read day from register 03h
+    day = I2C_Master_Read(1); // Read day from register 03h
     date = BCD_2_DEC(I2C_Master_Read(1)); // Read date from register 04h
     month = BCD_2_DEC(I2C_Master_Read(1)); // Read month from register 05h
     year = BCD_2_DEC(I2C_Master_Read(1)); // Read year from register 06h
diff --git a/ds3231.h b/ds3231.h
index c6a326a..3131310 100755
--- a/ds3231.h
+++ b/ds3231.h
@@ -2,9 +2,10 @@
 
 int BCD_2_DEC(int);
 int DEC_2_BCD(int);
+unsigned int Get_DayOfWeek(unsigned int, unsigned int,  unsigned int);
 void Read_Alarms_Temp(void);
 void Set_Date(void);
-void Set_DayOfWeek(void);
+void Set_DayOfWeek(int);
 void Set_Time(void);
 void Update_Current_Date_Time(void);
 void Write_Alarms(void);
\ No newline at end of file
-- 
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