Common

Please provide a chart comparing specifications (benchmarks) among VR Series devices.

See the following web page.
Click on a Series names listed at left or shown in the graphs or text to view a comparison chart.

http://www.necel.com/micro/english/product/vr/vr.html

Where should I direct inquiries about VR+ Linux?

MontaVista Software, Inc. provides Linux support for the VR Series.

The word "RFU" is frequently used in the VR4122 manual, but what does it stand for?

RFU stands for Reserved for Future Use.

The Application Notes warns that a watch exception may occur unless the watch low register (18), one of the CP0 registers, is initialized before executing a load/store instruction. However, the program samples show an instruction such as LI being executed before initialization.
Is this warning correct?

A watch exception will occur if a load/store instruction is executed for data whose physical address is indicated in either the watch low register and the watch high register.
Since the contents of these registers become undefined after a reset, if a load/store instruction is executed before initializing, undefined values will be used as the physical address when accessing data, which can cause a watch exception to occur.
Accordingly, it is best to initialize the watch low register first at the first stage of the initialization program.

Although the PMUCNTREG register must be accessed in order to reset the HALTimer, is it also true that access to this register is disabled unless the BCU is initialized?

No, there is no need to initialize the BCU before accessing this register.