After configuring a PVHVM FreeBSD guest with serial console access, using vim resulted in:

E437: terminal capability "cm" required

The Xen PVHVM tutorial uses this for /etc/ttys

ttyu0 "/usr/libexec/getty std.115200 dialup on secure

Using a more “modern”, capable console resolves this. For example:

ttyu0 "/usr/libexec/getty std.115200 vt100 on secure

Or theoretically for some colour:

ttyu0 "/usr/libexec/getty std.115200 vt102 on secure

As I’ve mentioned previously, now I want a DEC console.