From 7c8744d1e0961433aef3b7e9380c93b0999f32b8 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Sun, 18 Dec 2022 22:29:12 -0500
Subject: [PATCH] Read RTC date and time

---
 src/hulk/rtc.d | 112 +++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 100 insertions(+), 12 deletions(-)

diff --git a/src/hulk/rtc.d b/src/hulk/rtc.d
index 6f8e4af..93f8957 100644
--- a/src/hulk/rtc.d
+++ b/src/hulk/rtc.d
@@ -13,32 +13,67 @@ struct rtc
 
     private enum ubyte DISABLE_NMI = 0x80u;
 
-    private enum ubyte SR_A = 0xAu;
-    private enum ubyte SR_B = 0xBu;
-    private enum ubyte SR_C = 0xCu;
+    private enum ubyte REG_RTC_SECONDS = 0x0u;
+    private enum ubyte REG_RTC_MINUTES = 0x2u;
+    private enum ubyte REG_RTC_HOURS = 0x4u;
+    private enum ubyte REG_RTC_DAY = 0x7u;
+    private enum ubyte REG_RTC_MONTH = 0x8u;
+    private enum ubyte REG_RTC_YEAR = 0x9u;
+    private enum ubyte REG_SR_A = 0xAu;
+    private enum ubyte REG_SR_B = 0xBu;
+    private enum ubyte REG_SR_C = 0xCu;
 
+    private enum ubyte SR_A_RTC_UPDATE_IN_PROGRESS = 0x80u;
+    private enum ubyte SR_B_24HOUR = 0x02u;
+    private enum ubyte SR_B_BINARY = 0x04u;
     private enum ubyte SR_B_ENABLE_IRQ = 0x40u;
 
+    private static __gshared bool rtc_24hour_mode;
+    private static __gshared bool rtc_binary_mode;
+
+    static struct time
+    {
+        public ubyte year;
+        public ubyte month;
+        public ubyte day;
+        public ubyte hour;
+        public ubyte minute;
+        public ubyte second;
+    }
+
     public static void initialize()
     {
-        /* Enable IRQ 8 to receive RTC interrupts. */
-        out8(PORT_SELECT, DISABLE_NMI | SR_B);
-        ubyte sr_b = in8(PORT_DATA);
-        out8(PORT_SELECT, DISABLE_NMI | SR_B);
-        out8(PORT_DATA, sr_b | SR_B_ENABLE_IRQ);
+        time t = read_rtc_time();
+        klog.writefln("System time is 20%02u-%02u-%02u %02u:%02u:%02u",
+                t.year, t.month, t.day, t.hour, t.minute, t.second);
 
-        out8(PORT_SELECT, DISABLE_NMI | SR_A);
-        klog.writefln("SR_A = 0x%x", in8(PORT_DATA));
+        /* Enable IRQ 8 to receive RTC interrupts. */
+        ubyte sr_b = read_register(REG_SR_B, true);
+        write_register(REG_SR_B, sr_b | SR_B_ENABLE_IRQ, true);
+
+        rtc_24hour_mode = (sr_b & SR_B_24HOUR) != 0u;
+        rtc_binary_mode = (sr_b & SR_B_BINARY) != 0u;
 
         /* Send EOI to enable more RTC interrupts and re-enable NMIs. */
         eoi();
     }
 
+    private static ubyte read_register(ubyte register, bool disable_nmi = false)
+    {
+        out8(PORT_SELECT, register | (disable_nmi ? DISABLE_NMI : 0u));
+        return in8(PORT_DATA);
+    }
+
+    private static void write_register(ubyte register, ubyte value, bool disable_nmi = false)
+    {
+        out8(PORT_SELECT, register | (disable_nmi ? DISABLE_NMI : 0u));
+        out8(PORT_DATA, value);
+    }
+
     private static void eoi()
     {
         /* Read from status register C to clear the interrupt. */
-        out8(PORT_SELECT, SR_C);
-        in8(PORT_DATA);
+        read_register(REG_SR_C);
     }
 
     public static void isr()
@@ -53,4 +88,57 @@ struct rtc
         }
         eoi();
     }
+
+    private static time read_rtc_time()
+    {
+        time[2] times;
+        size_t reads;
+        do
+        {
+            times[reads & 1] = read_rtc_time_unsafe();
+            reads++;
+        } while ((reads < 2u) || (times[0] != times[1]));
+        return times[0];
+    }
+
+    private static time read_rtc_time_unsafe()
+    {
+        time t;
+        while ((read_register(REG_SR_A) & SR_A_RTC_UPDATE_IN_PROGRESS) != 0u)
+        {
+        }
+        t.year = read_rtc_time_register(REG_RTC_YEAR);
+        t.month = read_rtc_time_register(REG_RTC_MONTH);
+        t.day = read_rtc_time_register(REG_RTC_DAY);
+        t.hour = read_register(REG_RTC_HOURS);
+        t.minute = read_rtc_time_register(REG_RTC_MINUTES);
+        t.second = read_rtc_time_register(REG_RTC_SECONDS);
+        if (!rtc_24hour_mode)
+        {
+            ubyte pm = (t.hour & 0x80u) >> 7u;
+            t.hour &= 0x7Fu;
+            if (!rtc_binary_mode)
+            {
+                t.hour = bcd_to_binary(t.hour);
+            }
+            /* Hour is in 12-hour format; convert to 24-hour format. */
+            t.hour = cast(ubyte)((t.hour % 12u) + pm * 12u);
+        }
+        return t;
+    }
+
+    private static ubyte read_rtc_time_register(ubyte register)
+    {
+        ubyte value = read_register(register);
+        if (!rtc_binary_mode)
+        {
+            value = bcd_to_binary(value);
+        }
+        return value;
+    }
+
+    private static ubyte bcd_to_binary(ubyte bcd)
+    {
+        return (bcd & 0xFu) + ((bcd & 0xF0u) >> 4u) * 10u;
+    }
 }