Emulation of a disconnect of a device
View Patent ↗USB 2.0 supports communication in low-speed (LS), full speed (FS) and high speed (HS). In the full speed mode, the wire segment between a hub and a device is terminated via a pull-up resistor 480 on the D+ data line on the downstream end of the segment. In the high-speed mode, both signal wires are terminated by the LS/FS driver 420 generating a single-ended zero via resistors 490 . The device emulates a disconnect, while it operates in the high-speed mode, by activating the pull-up resistor 480 . Including the D+ pull-up resistor is practically equivalent to an open end, enabling a reliable disconnect detection in the hub using the disconnection envelop detector 460 . Detection of an (emulated) disconnect, triggers the reset en enumeration process. This allows the device to report a change in functionality without the user having to physically remove the device from the bus.
1. A method of emulating disconnection of a detachable device from a port of a communication bus, the method comprising:
controlling at least one switch of the detachable device such that prior to emulating disconnection of the detachable device from the communication bus the switch is open, whereby a bus line is terminated according to a first termination state; and
closing the switch of the detachable device such that the bus line is terminated according to a second termination state;
disabling a low speed/full speed driver of the detachable device;
at a hub of the communication bus, determining that the detachable device has been detached from the port of the communications bus in response to the closing and disabling even though the detachable device is still attached to the port of the communication bus;
in response to the determination that the detachable device has been detached from the communication bus, checking for a connection to the port of the communication bus;
detecting a connection between the detachable device and the port of the communication bus; and
resetting the detachable device in response to the detected connection.
2. A method of emulating a detachment of a detachable device from a port of a communication bus, the method comprising:
controlling at least one switch of the detachable device such that prior to emulating detachment of the detachable device from the port of the communication bus the switch is open, whereby a bus line is terminated according to a first termination state;
while the detachable device is still attached to the port of the communication bus, closing the switch of the detachable device such that the bus line is terminated according to a second termination state;
in response to closing the switch, determining that the detachable device has been detached from the port of the communications bus in response to the closing even though the detachable device is still attached to the port of the communication bus;
in response to determining that the detachable device has been detached from the communications, checking to see if a device is attached to the port of the communication bus;
detecting that the detachable device is attached to the port of the communication bus; and
resetting the detachable device in response to the detected attachment.
3. A method of emulating disconnection of a detachable device from a port of a communication bus, the method comprising:
controlling at least one switch of the detachable device such that prior to emulating disconnection of the detachable device from the port of the communication bus the switch is open, whereby a bus line is terminated according to a first termination state; and
closing the switch of the detachable device and disabling a low speed/full speed driver of the detachable device such that the bus line is terminated according to a second termination state, thereby triggering the port to:
determine that the detachable device has been detached from the port even though the detachable device is still attached to the port;
check to see if a device is attached to the port; and
initiate a reset process because the detachable device is still attached to the port.
4. The method of claim 1 further comprising, in response to the determination that the detachable device has been detached from the communication bus, reporting to a host of the communication bus that the detachable device has been detached from the communication bus even though the detachable device is still attached to the communication bus.
5. The method of claim 1 wherein resetting the detachable device comprises the hub asserting a single ended zero (SE0) signal.
6. The method of claim 1 wherein resetting the detachable device comprises initiating a Universal Serial Bus (USB) reset protocol.
7. The method of claim 2 further comprising, in response to the determination that the detachable device has been detached from the communication bus, reporting to a host of the communication bus that the detachable device has been detached from the communication bus even though the detachable device is still attached to the communication bus.
8. The method of claim 2 wherein resetting the detachable device comprises the hub asserting a single ended zero (SE0) signal.
9. The method of claim 2 wherein resetting the detachable device comprises initiating a Universal Serial Bus (USB) reset protocol.