Adjust RTC frequency to 32786 Hz

JOURNAL.md

@@ -3897,3 +3897,20 @@ Wrote a small tool `plictool` to dump the state of the PLIC:
 
 Interestingly, the auxiliar UART interrupts don't seem to be working very well.
 Also, is there another source 33 enabled?
+
+I have also noticed that the clock is running with the wrong frequency.
+Everything is about twice as slow. For example, `sleep 1` takes 2 seconds.
+So I assume the kernel thinks the clock goes faster than it actually does.
+
+The timer is at 50 KHz:
+
+    timebase-frequency = <50000>; /* 50 kHz */
+
+So, the frequency of this "clock" is done by using the "general" clock which
+goes at 50 MHz, and then using a simple counter that counts up to 1525, so the
+frequency is:
+
+    32786.88524590164 Hz
+
+Assuming that it actually works well. Let's try that and see if we can have a
+more realistic reading for the CLINT interrupt frequency.

ox-plic.dts

@@ -16,8 +16,10 @@
 	cpus {
 		#address-cells = <1>;
 		#size-cells = <0>;
-		/* Timer */
-		timebase-frequency = <50000>; /* 50 kHz */
+
+		// The RTC timer is clocked at the CPU frequency / 1525, so
+		// around 32786.88 Hz
+		timebase-frequency = <32786>;
 		CPU0: cpu@0 {
 			clock-frequency = <50000000>; /* 50 MHz */
 			device_type = "cpu";