USB OTG Function Controller
The USB On-The-Go specification has been introduced to provide a Low-cost connectivity solution for consumer portable devices such as mobile phones, PDAs, digital still cameras and MP3 players. Devices that are solely peripherals initiate transfers through a Session Request Protocol (SRP) while Dual-Role Devices support both SRP and Host Negotiation Protocol (HNP).
SI22USBOTG11 is user-configurable and individually programmable for Bulk/Interrupt or Isochronous transfers. Access to the FIFOs associated with these endpoints and to the internal Control / Status Registers is either via an 8 bit micro-controller bus.
Following are the two modes of operation that SI22USBOTG11 supports,
1. Peripheral mode
2. Host mode
When acting as a Peripheral, SI22USBOTG11 provides all the encoding, decoding and checking needed in sending and receiving USB packets – interrupting the CPU only when endpoint data has been successfully transferred. When acting as a Host, SI22USBOTG11 additionally maintains a Frame Counter and automatically schedules SOF. It also includes support for the Session Request and Host Negotiation Protocols required for point-to-point communications, details of which are given in the USB On-The-Go supplement to the USB 2.0 specification. The initial operation of SI22USBOTG11 (Host mode or in Peripheral mode) depends on whether it is being used as an A-device or a B-device. When SI22USBOTG11 is operating as an A-device, it is configured to operate in Host mode in which it generates transactions. When operating as a B-device, SI22USBOTG11 is configured to operate in Peripheral mode, which is same as a normal USB 2.0 peripheral. The SI22USBOTG11 determines whether it is the ‘A’ device by monitoring the ID pin on the mini-AB receptacle. Using HNP, the roles (Host or Peripheral) can be changed in runtime without the knowledge of the user.
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