USB and USB On The Go. May 28, 2003 Paul E. Berg MCCI

Transcription

1 USB and USB On The Go Paul E. Berg MCCI

2 Why Use USB? Multiple USB devices can operate in very close proximity no interference in a limited spectrum USB offers a relatively high data throughput sustained transfers of 6 Mbps (full speed) and 12 MBps (high speed) are fairly easily obtained the Cable includes Power either charge a battery or reduce the device power discharge 2

3 What Is USB? Five basic components Cables and Connectors Power Electrical Signaling Protocol Device Framework Standard commands Standard descriptions 3

4 What Is USB On The Go? A supplement to the USB 2.0 specification adding: New Connector Mini A plug Mini AB receptacle Dual Role Devices (DRD) works as a USB device works as a USB host Session Request Protocol (SRP) Host Negotiation Protocol (HNP) New rules for Power 4

5 Cables and Connectors 4 standard standard plugs 1 adapter adapter A socket to mini mini A plug 5

6 OTG Dual Role Device has a single mini AB receptacle Is A device A (host) when mini A A plug inserted Is B device B (device) when mini B B plug inserted operates at Full speed may operate at High Speed act as host to devices on targeted peripheral list may support one or more hubs (as an A device) A 6

7 OTG Dual Role Device (2) supports Session Request Protocol (SRP) allows B device B to request VBUS be turned on SRP is not supported through hubs supports Host Negotiation Protocol (HNP) Allows the B device B to talk to the A device A as a host avoids unplugging and turning the cable around HNP is not supported through hubs 7

8 OTG Dual Role Device (3) only A device A provides power (V BUS BUS ) 8 ma minimum V BUS power V BUS on on and no configured B device: B detect overcurrent (low voltage) == report B device B unsupported unsupported DRD B device B sees V BUS good good 150 µa A maximum V BUS load (not configured) SRP capable B device B sees V BUS good good 8 ma maximum V BUS BUS load (not configured) 8

9 USB IF Compliance USB IF has two new logos for OTG devices Full speed only OTG devices are expected to qualify for the left logo following the next USB IF Compliance Workshop (JULY 03) the compliance program for High speed capable OTG devices is currently under development 9

10 Frequently Frequently Wrong Asked Questions Answers

11 Frequently Wrong Answers There is only one sequence of steps taken to enumerate any specific USB device. WRONG Every operating system and/or version of OS has (or can have) its own sequence a device must respond to each (control transfer) request independently. 11

12 Frequently Wrong Answers Once a Control Transfer (SETUP transaction) arrives at a device, the host must complete it (through the Status stage) before another Control Transfer can start. WRONG There are error conditions where the host can abort a Control Transfer and send a new message which appears premature from the device s s perspective. [USB ] 12

13 Frequently Wrong Answers A host driver can assure that specific standard requests will not be sent to a device configured and operating under its control. WRONG The default pipe and therefore all standard control transfer access to a USB device is owned owned by the USB system stack. Any snooping utility or the system stack itself can, at the very least, make exploratory exploratory non disruptive standard requests at any time. 13

14 Frequently Wrong Answers The order transactions arrive at USB devices is the same order that those transactions were posted to the USB stack by the host drivers. WRONG The order of transactions carried by different pipes is not specified. Transactions posted to a single pipe move over USB in the sequence of their posting. Transactions to different devices, or to different pipes on the same device move over USB in any order the host chooses. 14

15 Frequently Wrong Answers OTG DRD cannot support low speed USB devices. WRONG If the device is on the DRD s Targeted Peripheral List the device is supported, regardless of it s s speed. If the device is not on the DRD s Targeted Peripheral List the device need not be supported, regardless of it s s speed. A device that is not listed on the Targeted Peripheral List may or may not be supported by a DRD the rule is No silent failures. 15

16 Frequently Wrong Answers OTG DRD provides no more than 8 ma of V BUS BUS. WRONG Minimum power provided by DRD is 8 ma. There is no maximum maximum power (other than safety) and/or 500 ma as per a USB 2.0 high power port. 16

17 Frequently Wrong Answers An On The The Go DRD in the A device A position can have its battery recharged during an HNP session if the B device B selects a configuration specifying 100 ma of power or more (up to 500 ma). WRONG The A device A always provides all power on V BUS. When during an HNP session the B device B selects a configuration, the power setting is meaningless. A DRD may be able to recharge batteries via USB the DRD in the B device B position can draw the power indicated in the configuration selected by the host during enumeration. 17

18 Frequently Wrong Answers Any USB device with a battery is self powered. WRONG The device manufacturer determines if a device is bus powered or self powered. Certainly any device that uses only power from V BUS to recharge its battery is bus bus powered powered. A device which claims it uses no power in any of it s configurations (precluding a battery charge from V BUS ) must be self powered. 18