CPU requirements and real time

docs/notes.md

@@ -8,6 +8,23 @@ the 64-bit "bullseye" version of Raspberry Pi OS for the Raspberry Pi
 customizations. As of this writing it has not yet incorporated Debian version 12.)
 Older versions may work, but you may have to fix some problems.
 
+Most reasonably modern x86 systems will run *ka9q-radio* just
+fine. Even an Intel i5 can handle the RX888 at its full sample rate of
+130 MHz with plenty of time left over.  But be careful with other
+CPU-intensive tasks on the same system, even at a high 'nice' level,
+unless you are running a realtime-enabled version of the Linux
+kernel. *ka9q-radio* can use the Linux real-time scheduling features
+only if the kernel supports them. (Debian provides both realtime and
+standard kernels for each release). The RX888 works fine on the Orange
+Pi **until** you try to run CPU soakers; then *ka9q-radio* begins to
+badly lose data. AI6VN and I believe this is because the standard OPi
+kernel is not real-time enabled, and we can't find and install one
+that is.
+
+The Raspberry Pi 4 is sufficient to handle the Airspy R2 (20 Ms/s
+real) even with several hundred channels, but it is *not* fast enough
+for the RX888 except at low sample rates.
+
 Supported Hardware and System Requirements
 ------------------------------------------