1 files changed, 101 insertions, 0 deletions

diff --git a/rsnix/src/rtc.rs b/rsnix/src/rtc.rs
new file mode 100644
index 0000000..535f32e
--- /dev/null
+++ b/rsnix/src/rtc.rs
@@ -0,0 +1,101 @@
+// ---------------------------------------------------------------------------
+// RTC/CMOS clock — the standard PC real-time clock on ports 0x70/0x71.
+//
+// Reads the time registers (0x00-0x09).  Values may be BCD or binary and
+// hours may be 12- or 24-hour depending on status register B; we normalize
+// to binary 24-hour.  The century register (0x32) is used when it reports
+// a sane value, otherwise we assume 2000+.  NMI is masked (bit 7 set) while
+// poking CMOS — this kernel has no NMI handler, so a stray NMI would fault.
+// ---------------------------------------------------------------------------
+
+pub struct DateTime {
+    pub year: u16,
+    pub month: u8,
+    pub day: u8,
+    pub hour: u8,
+    pub minute: u8,
+    pub second: u8,
+}
+
+/// Read one CMOS register.  Writes bit 7 to the address port, which masks
+/// NMIs during the access.
+fn cmos_read(reg: u8) -> u8 {
+    unsafe {
+        core::arch::asm!(
+            "out dx, al",
+            in("dx") 0x70u16,
+            in("al") reg | 0x80,
+            options(nomem, nostack, preserves_flags)
+        );
+        let val: u8;
+        core::arch::asm!(
+            "in al, dx",
+            out("al") val,
+            in("dx") 0x71u16,
+            options(nomem, nostack, preserves_flags)
+        );
+        val
+    }
+}
+
+fn bcd_to_bin(v: u8) -> u8 {
+    (v & 0x0F) + (v >> 4) * 10
+}
+
+/// Read the current wall-clock time from the RTC.
+pub fn now() -> DateTime {
+    // Wait until an in-progress update finishes (status A, UIP bit 7).
+    while cmos_read(0x0A) & 0x80 != 0 {
+        core::hint::spin_loop();
+    }
+
+    let reg_b = cmos_read(0x0B);
+    let bcd = reg_b & 0x04 == 0; // bit 2: 0 = BCD, 1 = binary
+    let hour12 = reg_b & 0x02 == 0; // bit 1: 1 = 24-hour, 0 = 12-hour
+
+    let mut second = cmos_read(0x00);
+    let mut minute = cmos_read(0x02);
+    let mut hour = cmos_read(0x04);
+    let mut day = cmos_read(0x07);
+    let mut month = cmos_read(0x08);
+    let mut year = cmos_read(0x09);
+    let century = cmos_read(0x32);
+
+    if bcd {
+        second = bcd_to_bin(second);
+        minute = bcd_to_bin(minute);
+        hour = bcd_to_bin(hour);
+        day = bcd_to_bin(day);
+        month = bcd_to_bin(month);
+        year = bcd_to_bin(year);
+    }
+    if hour12 {
+        let pm = hour & 0x80 != 0; // top bit of a 12-hour hour is the PM flag
+        hour &= 0x7F;
+        if hour == 12 {
+            hour = 0; // 12 AM/PM are both 0 in 24-hour form
+        }
+        if pm {
+            hour += 12;
+        }
+    }
+    let year = {
+        let full = century as u16 * 100 + year as u16;
+        if (1970..=2200).contains(&full) {
+            full
+        } else {
+            // Unreadable century register (QEMU returns garbage here) —
+            // assume 2000+ for the 2-digit year.
+            2000 + year as u16
+        }
+    };
+
+    DateTime {
+        year,
+        month,
+        day,
+        hour,
+        minute,
+        second,
+    }
+}