Crystal LAN CS8920, Техническое справочное руководство, Страница: 48 / 67

AN84REV1 48
CS8920 Technical Reference Manual
utilized by the CS8920 in its current
operational mode (e.g., IO mode only -- no
shared memory or DMA channel required).
Therefore, in order to avoid wasting ISA
resources and decrease the likelihood of an
unsuccessful autoconfiguration of the
CS8920 or other PnP device, the resource
descriptor for those resources not used
should be omitted from the resource
descriptor list.
One exception to this guideline concerns
the resource descriptors for the BootPROM
(Memory Descriptor 0) and shared memory
for memory-mapped access to the
PacketPage registers (Memory Descriptor
1). Memory Descriptor 1 will only be
processed if Memory Descriptor 0 is
defined. Therefore, if shared memory is
used (Memory Descriptor 1), a resource
descriptor for a BootPROM (Memory
Descriptor 0) must be placed in the
descriptor list regardless of whether or not a
BootPROM is used.
Note: Some PnP BIOSs have been observed
to ignore a memory descriptor with a range
length of zero bytes. Therefore, to provide
compatibility with as many BIOS versions
in the field as possible, yet keep the amount
of unused memory reserved by PnP to a
minimum, Crystal suggests using a 256-
byte range length value for Memory
Descriptor 0 when a BootPROM is not
used but shared memory is requested.
Figure 3.4.1 below is an example PnP
resource data record for a CS8920 ISA
Ethernet Adapter. This example assumes
the CS8920 will use IO space, shared
memory, IRQ, DMA, and a BootPROM is
installed. The record starts at EEPROM
word address 30h.
Refer to Section 6.2 of the Plug and Play
ISA Specification 1.0a for more
information on Plug and Play resource data
types.