37.6 Functional Description

In Device mode, the Hi-Speed USB module encodes, decodes, checks, and directs all USB packets sent and received. IN transactions are handled through the device’s TX FIFOs, OUT transactions are handled through its RX FIFOs. Control, Bulk, Isochronous and Interrupt transactions are also supported.

In Embedded Host mode, the way in which the Hi-Speed USB module behaves depends on whether it is linked up for point-to-point communications with another USB system or whether it is attached to a hub. When attached directly to a USB system operating as a Device, the module offers the range of capabilities needed to act as the host in point-to-point communications with this USB system. When attached through a USB hub, the Hi-Speed USB module can perform the functions required to act as the host for multiple USB Devices simultaneously.

When operating in Embedded Host mode and used for point-to-point communications with a single other USB device (which can be Hi-Speed, Full-Speed, or Low-Speed), the Hi-Speed USB module can support Control, Bulk, Isochronous or Interrupt transactions. IN transactions are handled through the RX FIFOs, OUT transactions are handled through the TX FIFOs. As well as encoding, decoding and checking the USB packets sent and received, the module will also automatically schedule Isochronous endpoints and Interrupt endpoints to perform one transaction every ‘n’ frames/micro-frames (or up to three transactions if the high-bandwidth option is selected), where ‘n’ represents the polling interval that has been programmed for the endpoint. The remaining bus bandwidth is shared equally between the Control and Bulk endpoints.

When attached to a single or multiple USB devices through a USB hub, the Hi-Speed USB module continues to offer the facilities previously mentioned, but it needs to be further configured for the following functional overlays:

• The function address of the target device
• The operating speed of the target device (so that the appropriate speed conversion can be carried out)
• If the target device is a Full-Speed or Low-Speed device that is accessed through a Hi-Speed hub, the endpoint additionally needs to be configured with the function address and port number of the hub

The initial operating role of the Hi-Speed USB module (Embedded Host mode or Device mode) depends on orientation of the Micro-AB cable. The orientation of the Micro-AB cable determines the logic state of USBID input pin. The USBID low state indicates the connection of the Micro-A side of the Micro-AB cable and initial operation in the Embedded Host role. The USBID high state indicates the connection of the Micro-B side of the Micro-AB cable and initial operation in the Device role. The cable orientation state of USBID can be superseded using the IDOVEN and IDVAL bits of the CTRLA register.

The HOSTREQ bit is provided in the DEVCTL register of the Hi-Speed USB module which can trigger a Host Negotiation, requesting that the system currently operating in the Device role swap to the Embedded Host role during the next USB bus idle period. Information about the current operating role and current bus connection speed can be found in the DEVCTL register.

The Hi-Speed USB module has 9kB of dedicated RAM that can be dynamically allocated between the endpoint FIFOs.

The Hi-Speed USB module has a dedicated, 8-channel DMA controller that can be set up to load/unload the endpoint FIFOs. Each of the DMA channels can be configured to operate in one of two modes:

• DMA Mode 0: Allows one packet to be automatically transferred to/from its respective endpoint FIFO
• DMA Mode 1: Allows for a complete Bulk transfer to be setup and automatically transferred to/from its respective endpoint FIFO

The Hi-Speed USB module has a set of common registers and a set of indexed registers for configuration of the individual endpoints. The indexed endpoint configuration registers are accessed for a specific endpoint by selecting that endpoint using in the INDEX register. For additional information on the configuration and operation of the Hi-Speed USB module, please refer to the documentation, firmware and application examples provided by Microchip and third-party solution providers for PIC32 products. For information about fully USB IF compliant middleware, please refer to available third-party solutions.

The Hi-Speed USB module supports operation in Hi-Speed (480 Mb/s), Full Speed (12 Mb/s) and Low Speed (1.5 Mb/s).

• Hi-Speed operation can be enabled or disabled using the HSEN bit in the POWR register.
• Operation in Full-Speed and Hi-Speed modes can be forced in the TESTMODE register for testing purposes.
• The operating speed is set using the SPEED bits of the configuration registers for the individual endpoints.