Polling rate

The polling rate of a keyboard (or other input device) can mean two things:

• The maximum rate at which a USB HID device is able to present reports over USB
• How often the physical keyboard matrix (or other input) is scanned

Polling rate does rarely indicate actual response time. (Time from mechanical event and reception of that event at the host)

Most types of keyboard switches have a contact mechanism that requires debouncing of its electric signal during a period before the signal is considered stable enough to be considered a change in key state. That period is typically between five and thirty milliseconds. The switch/matrix is often polled multiple times during that period.

Because USB is a host-controlled interface, polling of USB HID devices is done by the host. Each device tells the host its maximum polling rate but USB hosts are not at all required to poll devices at their maximum rates. The maximum theoretical USB polling rate is 1000 Hz (every 1 ms).