USB2.0协议解析

Isochronous Transfers --constant-rate, error tolerant transfers Interrupt Transfers –send or receive data infrequently but with
bounded service periods.
Device state
Operations
• • • • • • • Dynamic Attachment and Removal Address Assignment Configuration Data Transfer Power Management Request Processing Request Error
Token packet
data packet
Handshake packet
Isochronous Transactions have no handshake phase In the host controller error cases, the host controller implements the “three strikes and you’re out” mechanism. That is, it increments an error count (err_count) and, if the count is less than three, it will retry the transaction.
Sync field
The SYNC pattern used for low-/full-speed transmission is required to be 3 KJ pairs followed by 2 K’s for a total of eight symbols. The SYNC pattern used for high-speed transmission is required to be 15 KJ pairs followed by 2 K’s, for a total of 32 symbols. It is used by the input circuitry to align incoming data with the local clock
Pipe
A USB pipe is an association between an endpoint on a device and software on the host
Message Pipes --has some USB-defined structure, control transfer type Stream Pipes --has no USB-defined structure, bulk, isochronous, and interrupt transfer types
USBD:
The USBD provides a collection of mechanisms that operating system components, typically device drivers, use to access USB devices • • • • Configuration via command mechanisms Transfer services via both command and pipe mechanisms Event notification Status reporting and error recovery
zylia
Motivation PC-telephone connection Ease-to-use Port expansion
History USB1.0 USB1.1 USB2.0 USB3.0 USB3.1
low speed(LS) -1.5Mbps 1996 full speed(FS) -12Mbps 1998 high speed(HS) -480Mbps 2000 super speed(SS) -5Gbps 2008 super speed+(SS+) -10Gbps 2013
Interface
A USB logical device appears to the USB system as a collection of endpoints. Endpoints are grouped into endpoint sets that implement an interface. Interfaces are views to the function. Client software manages an interface using pipe bundles (associated with an endpoint set)
Hubs provide the electrical interface between USB devices and the host.
• • • • • Connectivity behavior Power management Device connect/disconnect detection Bus fault detection and recovery High-, full-, and low-speed device support
Layers
Physical bus topology
Physical bus topology --Multiple Full-speed Buses
Logical bus topology
Client bus topology
Endpoint pipe interface
Endpoint
Controller Duties:
•State Handling •Serializer/Deserializer •(micro)frame Generation •Data Processing •Protocol Engine •Transmission Error •Handling •Remote Wakeup
Three layers:
USB bus interface -- Host Controller Driver,HCD USB system -- USB Driver,USBD Client -- Host Software
Capabilities: •Detecting the attachment and removal of USB devices •Managing USB standard control flow between the host and USB devices •Managing data flow between the host and USB devices •Collecting status and activity statistics •Controlling the electrical interface between the Host Controller and USB devices, including the provision of a limited amount of power
Architecture
Split
USB defines a special token for split transactions: SPLIT The split transaction token is used to support split transactions between the host controller communicating with a hub. There are two split transactions defined that use the SPLIT special token: a start-split transaction (SSPLIT) and a complete-split transaction (CSPLIT). This approach allows the host controller to start a full-/low-speed transaction via a high-speed transaction and then continue with other high-speed transactions without having to wait for the full-/low-speed transaction to proceed/complete at the slower speed.
Transfer types
Control Transfers --Control transfers are intended to support
configuration/command/status type communication flows between client software and its function.
Packet field
The PID indicates the type of packet and, by inference, the format of the packet and the type of error detection applied to the packet. It is used by the input circuitry to align incoming data with the local clock.
The start of a packet (SOP) is signaled by the originating port by driving the D+ and D- lines from the Idle state to the opposite logic level (K state) The SE0 state is used to signal an end-of-packet (EOP). EOP will be signaled by driving D+ and D- to the SE0 state for two bit times followed by driving the lines to the J state for one bit time.