USB Complete fourth- P47

USB Complete fourth- P47:This book focuses on Windows programming for PCs, but other computersand operating systems also have USB support, including Linux and AppleComputer’s Macintosh. Some real-time kernels also support USB.
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USB Complete fourth- P47Chapter 18 6GUVA2CEMGV Value. 04h. Action. Repetitively transmit the test packet defined by the USB specification. Purpose. Test rise and fall times, eye pattern, jitter, and other dynamic wave- form specifications. 6GUVA(QTEGAPCDNG Value. 05h. Action. Enable downstream-facing hub ports in high-speed mode. Packets arriving at the upstream-facing port are repeated at the port being tested. The disconnect-detect bit can be polled while varying the loading on the port. Purpose. Measure the disconnect-detection threshold. 1VJGT 8CNWGU Test-mode values 06h through 3Fh are reserved for future standard tests. Values C0–FFh are available for vendor-defined tests. All other values are reserved.5WRGT5RGGF SuperSpeed’s fast, dual-simplex interface and new power-management capabili- ties require different encoding, packet formats, and low-level protocols. A SuperSpeed transmitter scrambles and encodes data to be sent on the bus. A SuperSpeed receiver decodes and de-scrambles the received data.&CVC 5ETCODNKPI Data scrambling eliminates repetitive patterns in the data. Doing so spreads the radiated EMI over a wider frequency spectrum and helps in meeting FCC requirements. To scramble data to be transmitted, a free-running linear feed- back shift register implements a polynomial defined in the USB 3.0 specifica- tion. The transmitter XORs the output of the shift register with the data bits. Descrambling uses a complementary mechanism to recover the unscrambled data.PEQFKPI SuperSpeed uses 8b/10b data encoding as specified in ANSI INCITS 230-1994. Other interfaces that use this encoding include PCI Express, Gigabit436 Packets on the Bus Ethernet and IEEE-1394b. The encoding converts each byte value to a 10-bit Data Symbol for transmitting. The encoded data has no more than five ones or zeroes in series and contains equal numbers of ones and zeroes over time. As with USB 2.0 data, frequent transitions enable the receiver to synchronize with the transmitted data without requiring a separate clock line. The roughly equal numbers of transmitted ones and zeroes provide DC balance, which prevents errors that could occur due to a DC component in the signal. The encoding also enables error detecting by monitoring the number of received ones and zeroes over time. Because the encoded data has more bits than the data being encoded, extra symbols are available to perform special functions. Data Symbols represent val- ues from 00h to FFh and Special Symbols perform functions used in framing data and managing link-level communications. The SuperSpeed signaling rate, or speed of the bits on the wires in each direc- tion, is 5 Gbps. The USB 3.0 specification refers to the rate as 5 GT/s (GigaTransfers per second). The 8b/10b encoding increases the number of bits to be transmitted by 25%, so 5 Gbps on the bus translates to 4 Gbps, or 500 MB/s, of unencoded data. Framing, error detecting, and other protocols reduce the theoretical maximum data throughput to around 400 MB/s in each direc- tion. SuperSpeed links use low-frequency periodic signaling (LFPS) for exiting low-power states and performing Warm Resets. The signaling consists of bursts of a frequency for a specified time and repeat rate. The LFPS frequency is in the range 10–50 MHz, is easy to generate, and uses little power..KPM .C[GT A SuperSpeed link is the physical and logical connection between two ports. The physical connection consists of a cable segment and the two ports, or link partners, the cable connects. The link partners manage the link by communi- cating via link commands and other signaling on the link when the wires aren’t carrying other traffic. Each port provides state machines and buffers to manage the connection and data transfers with the link partner. State machines generate link commands to acknowledge received header packets, recover from errors, implement flow control, and manage power on the link. An upstream-facing port must detect when its link has been idle for 10 µs and send a special link command to indicate that the port is present. Link commands transmit when the link isn’t carrying Transaction Packets. Downstream-facing ports detect 437Chapter 18 device connection and removal and wakeup signaling. Link-layer protocols define how the link manages buffers, frames packets, and detects received pack- ets. The link layer also handles training and synchronizing to establish connec- tivity between a device (which may be a hub) and its upstream link partner. To synchronize, a link partner transmits defined series of bytes called Ordered Sets, which the receiving link partner detects.4GUGV SuperSpeed defines two major categories of reset. A PowerOn Reset restores memory, registers, and other storage in the device to their default power-on states. An InBand Reset resets port settings and places the link in the U0 state while remaining powered. Two types of InBand Reset are the Warm Reset and Hot Reset. A Warm Reset uses low frequency periodic signaling and takes around 100 ms. A Hot Reset uses link-level training sequences of Ordered Sets, is much faster, and leaves more settings unchanged in the device. The host requests an in InBand reset by issuing a hub-class Set Port Fea- ture(Port_Reset) or SetPortFeature(BH_Port_Reset) request to the hub that is the target device’s link partner. On receiving a request for a BH_Port_Res ...