HP Visualize c360 - Workstation Manuale
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Do You Need to Know About USB?
Several PA-RISC workstations to be intro-
duced during 1999 require a USB keyboard
and mouse. Apart from the addition of three
PC-style keys to the keyboard and a scroll
wheel to the mouse, most users won’t notice
the difference once the system is set up. And
the person setting up the system is likely to
notice only a different connector shape.
However, you need to absorb this presentation:
• if you plan to supply your own keyboard or mouse, or
• if you have been using other PS/2 devices, or
• if you have been considering a port of a PC or iMac USB device, or
• if you need a keyboard and mouse cable longer than 2.5m, or
• if you simply lament the passing of HP-HIL.
This presentation does not apply to Intel-based VISUALIZE workstations, as they
have had USB ports for some time (as have most PCs), and like all NT Worksta-
tions, are awaiting Windows 2000 (aka NT 5) for full USB support.
What You Will Learn Here
• What is it? USB in a nutshell.
• Some history - how USB got to where it is today.
• The state of the USB standard and Unix API efforts.
• Key technical details for users and the merely curious.
• The capabilities, limitations and applications for USB.
• How USB compares to legacy and contemporary alternatives.
• How USB will roll out on PA-RISC platforms.
• How USB is supported in PA-RISC hardware, firmware and HP-UX.
• The initial USB devices.
• Considerations for buyers and users at the transition.
• Considerations for developers.
What is USB?
• U.S.B. stands for Universal Serial Bus (Logo: Icon: )
• Moderate speed 12 Mbps/sec. or 1.5 Mbytes/sec.
• Multiple devices up to 126 - on a single resource set.
• Cubicle span cabling 5m per segment, 30m max. with hubs
• Flexible topology tiered star
• Flexible power devices bus- or locally-powered, w/suspend-resume APM
• Robust PnP, hot attach-detach1
• Low-cost 4 wire
• Idiot-proof Unique modular connectors:
Style A (upstream, to hub/host):
Style B (downstream, detach at device):
Although USB ports have been shipping on PCs for over two years,
widespread acceptance has been delayed by lack of
devices, which, in turn, have been awaiting:
• O.S. support: Still waiting for “NT”. Win95 support is problematic.
• BIOS support: Most “USB” PCs have no USB console capability in BIOS.
• Economics: Some PS/2 devices are still cheaper than USB during 1999.
1. Hot attach-detach is planned, but not fully implemented in the first HP-UX USB support.
A
B
How USB Got Here
As with PCI, USB is sponsored by an independent consortium that was initiated by
Intel. Work began on the standard in 1993.
USB was a response to several issues:
1. PS/2, RS-232C serial and parallel (Centronics, ECP, EPP, IEEE-1284) have seri-
ous deficiencies, and occupy too much panel space in a shrinking world.
2. Dedicated ISA cards are vanishing. SCSI and dedicated PCI cards are overkill
for many desktop applications. FDD and IDE are too resource-limited for many
devices that might otherwise use them.
3. It was getting increasingly expensive for suppliers to maintain proprietary desk-
top connectivity solutions such as ADB (Apple Desktop Bus), Access.Bus,
AT&T CHI (Concentration Highway Interface), Apple GeoPort and HP-HIL.
4. The IRQ shortage in the Intel architecture isn’t going to be solved by adding
more IRQs.
5. An intelligently implemented new interface could revolutionize the desktop,
enabling new capabilities, lower development cost, lower prices, and dramatic
improvements in supportability and ease of use.
$
USB Standards Report
There are two hardware Host Controller Interface architectures:
UHCI (Universal), and OHCI (Open). UHCI appears on Intel motherboards.
OHCI is predominant elsewhere - and is what PA-RISC workstations will use.
The underlying USB Standard is presently at release 1.1. {http://www.usb/org}
Driver Classes have been defined by Working Groups for ( - release level)
MS Windows API Status:
Windows provides legacy thunking code for well-behaved drivers.
The status of open Win32 USB APIs is not clear.
Unix API Status (USBDI) is at 0.8. {URL pending}
As is traditionally the case in the Unix community, standards development is well
behind implementations. USBDI APIs rely on UDI Meta Language. We’ll all need to re-
write or thunk new libraries later (and implement UDI).
Common - 1.0 Hub - 1.0 Physical I/F - 1.0
Audio - 1.0 Imaging - 1.0 Power - 1.0
HID (Human I/F Device) - 1.0 InfraRed - 0.9 Printing - 1.0
Communications - 1.09 Monitor Control - 1.0 Vendor-Specific - N/A
%
A Closer Look
• Devices may be compound (have multiple
functions) or contain hubs.
• Devices are high-speed (12 Mbps) or low-
speed (1.5 Mbps) only. Hubs are high only.
• Differential Data Signalling (3.3V NRZI)
• +Vcc is 500mA @ 5 Vdc
• Devices may supply own power.
• Vcc and Ground make contact before Data lines.
• Maximum length of any single Hub-Device segment:
• Maximum length to any (high speed) device (5 external hub tiers):
• Connectors are friction/detent capture only, and may not be suitable for moderate or
high shock/vibration environments (without user-designed capture).
+Vcc
-Data
+Data
Ground
Hub Device
5m
3m for low-speed devices
Root Hub Hub DeviceHub HubHub Hub
30m
"
USB Topology - “Tiered Star”
• Only devices (not other hubs) may be connected to an un-powered hub.
Root Hub
Hub
Hub Hub
Hub
Hub
Hub
Device
Device
Device
Device
Device
Device
Hub
Device
Hub
Device
Device
Device
Device
Device
Device
Device
Device
Device
1
2a
3a
4
5 (max. powered
Max. device depth
hub depth)
2b
3b
3c
#
USB at the Limits
Disallowed:
• Host-to-host direct cabling. Host-to-host solutions exist, but presently require
LAN adaptors, modems or null modems in the cabling path, none of which are
transparent extensions of the USB. It is not yet clear if any true bridges or
remote-repeaters for USB will appear (the equivalent of LAN bridges, the HP
46082A/B HIL extensions or the HP 37204A HP-IB extender).
Strongly Discouraged:
• Style A (receptacle) to Style A (plug) passive extension cables. Notwithstanding,
they do exist, and can lead to specification violations and unreliable operation.
Exception: active cables (5m single-port bus-powered hubs also exist - and
they’re legal, as long as they aren’t used to interconnect hubs).
Performance:
• Of the theoretical “1.5 MByte/sec.” available, in practice, typical sustained
throughput is more like 600 KBytes/sec., about 33% lower than asynchronous
SCSI (which doesn’t provide its theoretical 1.5 MB/s either). The fastest USB
device reported to date is a Belkin host-to-host LAN emulator, at 700 KBytes/sec.
The Uses of USB
Ideal Uses
• Most human input devices: bar code, buttons, digitizers, gaming, gloves, joy-
sticks, keyboards, knobs, light-pens, mice, 6-axis, tablets, trackballs, touch-pads
• Modem & telephony: POTS, FAX, ISDN, T1, ADSL, low-end cable modem
• Printers, up through 40 ppm or so
• Simple audio: MIDI, speakers, mono&stereo I/O, 5.1 compressed surround out-
put (moving the audio codec outside the box has benefits but overhead hazards)
• Low-demand imaging: digital still cameras, low-rate and/or low-resolution
motion video (e.g. conferencing), monitor calibrators, custom displays, monitor
control
• External floppy drives (FDD, LS-120, HiFD, ZIP)
• Legacy adaptors (USB-IR, USB-serial, USB-parallel, USB-PS/2)
• Security authentication: biometric input, dongles, intrusion detection
• Power management: UPS, cryo-cooler control
Hot-attach/detach permits simple (albeit break-before-make) console switching,
and the 5m segment length can handle most server rack situations.
Questo manuale è adatto per i seguenti modelli
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