Usb Microcontroller Transfer Characteristics

The USB Microcontroller devices and the port work in tandem and the host guarantees bandwidth to isochronous endpoints

. This bandwidth guarantee is a feature unique to isochronous endpoints. The amount of bandwidth allocated to a particular isochronous endpoint is determined by information requested by that endpoints descriptor. Data transfers take place inside USB data frames. For Full Speed USB devices such as the Silicon Laboratories C8051F32x, a data frame spans 1 millisecond.

A device can be configured to transmit as few as 1 byte per frame or as many as 1023 bytes per frame. The USB specification defines IN and OUT designations from the perspective of the host, meaning that IN

endpoints transmit data to the host and OUT endpoints receive data from the host. During every 1 millisecond interval during communications operation, the host signals isochronous IN endpoints to transmit bytes to the host, and signals isochronous OUT endpoints to receive bytes from the host.

Unlike other transfer types, isochronous transfers have no hardware-controlled handshaking or error-checking ability, so errors may occur occasionally. Systems must be able to recover from occasional errors without the help of hardware.

The USB microcontroller specification defines IN and OUT designations from the perspective of the host, meaning that IN endpoints transmit data to the host and OUT endpoints receive data from the host. During every 1 millisecond interval during communications operation, the host signals isochronous IN endpoints to transmit bytes to the host, and signals isochronous OUT endpoints to receive bytes from the host.

Unlike other transfer types, isochronous transfers have no hardware-controlled handshaking or error-checking ability, so errors may occur occasionally. Systems must be able to recover from occasional errors without the help of hardware.

by: Chris Bartik

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