kern/56059: speaker(4): system hangs if tone < 100 Hz (_SC_CLK_TCK) is played

[rvp%SDF.ORG@localhost]

>Number:         56059
>Category:       kern
>Synopsis:       speaker(4): system hangs if tone < 100 Hz (_SC_CLK_TCK) is played
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Mar 16 12:20:00 +0000 2021
>Originator:     RVP
>Release:        NetBSD-HEAD/amd64 9.99.81 (built 202103152150Z)
>Organization:
>Environment:
NetBSD-HEAD/amd64 9.99.81 (built 202103152150Z)
>Description:
Play a tone < 100 Hz using /dev/speaker. System hangs.

# echo o0 C > /dev/speaker
# echo n1 > /dev/speaker

These command work:

# echo o1 C > /dev/speaker
# echo n9 > /dev/speaker

The latest 9.1-STABLE also behaves the same.
>How-To-Repeat:
See commands above.
>Fix: