initial import

rtc.lsp

@@ -0,0 +1,57 @@
+(defvar *rtc-port* 0)
+
+(defun bcd-to-dec (x)
+   "(bcd-to-dec x)
+Convert the BCD-encoded number x to a decimal value."
+   (+
+      (* 10 (ash x -4))
+      (logand x #xf)))
+
+(defun dec-to-bcd (x)
+  "(dec-to-bcd x)
+Converts the decimal value to a BCD-encoded number.
+Number must be in the range 0 to 99."
+  (+
+    (ash (floor x 10) 4)
+    (logand (rem x 10) #xf)))
+
+(defun rtc-p ()
+  "(rtc-p)
+Returns t if the RTC is connected."
+  (with-i2c (str *rtc-port* #x68)
+	    (streamp str)))
+
+(defun rtc-set (h m s)
+ "(rtc-set hr min sec)
+Set the time on a DS3231 RTC. Times are in BCD, so use
+the appropriate reader macro, e.g. (rtc-set #x12 #x34 #x00)
+for 12:34:00."
+  (let ((h (dec-to-bcd h))
+	(m (dec-to-bcd m))
+	(s (dec-to-bcd s)))
+    (with-i2c (str *rtc-port* #x68)
+	      (write-byte 0 str)
+	      (write-byte s str)
+	      (write-byte m str)
+	      (write-byte h str))))
+
+(defun rtc-get ()
+  (with-i2c (str *rtc-port* #x68)
+    (write-byte 0 str)
+    (restart-i2c str 3)
+    (mapcar bcd-to-dec
+      (reverse
+        (list
+          (read-byte str)
+          (read-byte str)
+          (read-byte str))))))
+
+(defun rtc-now ()
+ "(rtc-now)
+Set the time using the RTC."
+  (apply now (rtc-get)))
+
+(defun now-rtc ()
+  "(now-rtc)
+Sets the RTC time using the now function."
+  (apply rtc-set (now)))