System information

5.1 USB Device Emulation
AHB
HPI
Bridge
CHARM
Register
AHB Bus
USB
Chip
16
Internal
USB Plug #2
Internal
USB Plug #1
External
USB Plug #2
External
USB Plug #1
Card Bracket
Onboard
PLD
Stripe
PLD
Bridge
Figure 5.2: HPI Bridge
illustrate this process. The VNC server (explained in section 4.2.3) converts the keyboard
interaction inside a connected VNC client into USB keycodes. The USB mouse emulation
functions in the same way like the keyboard emulation. By default, an interrupt endpoint
provides the data of a USB keyboard or a USB mouse. However, an interrupt endpoint
or the related interrupt pipe does not sent a signal which informs the host. Instead, the
interrupt endpoint is read out periodically by the host.
5.1.4 Mass Storage Device
A mass storage is a storage of large amounts of information in a persisting and machine-
readable fashion. The CHARM card emulates a USB storage device to provide a boot
device which can be used to install an operating system on the host system. Additionally,
a boot device can contain a program updating the BIOS of the system. Basically, the
CHARM card supports two types of mass storage devices: a CD-ROM or a flash memory
device. The emulated CD-ROM device provides an ISO image
6
to the host system. The
most of the installation software for operating systems can be obtained as an ISO image.
In contrast, the flash memory device contains floppy disk images of an MS DOS file system.
BIOS update utilities are normally DOS programs which have to be stored on such a file
system. Modern mainboards support the "El Torito standard" [71]. It is an extension to
the ISO 9660 CD-ROM specification. This standard permits the booting of a floppy or hard
disk image from a CD-ROM. Thus, the CHARM card provides normally a USB CD-ROM
device which can provide ISO and floppy images.
6
An ISO image is a disk image of an ISO 9660 file system.
69