user manual

Software Developer’s Manual 207
Dual Port Characteristics
The result of multiple LAN devices’ reading EEPROM is that power-on and reset-initiated
EEPROM read sequences might appear slightly differently from the sequences illustrated during
the discussion of power-state transitions (Section 6.3.2). Those illustrations indicate EEPROM
read periods without distinguishing between reads by LAN A versus LAN B devices. At initial
power-on, both LAN devices always execute an EEPROM read sequence. However, since the
enabling/disabling of a particular LAN device occurs on the deassertion of PCI reset, the post-reset
EEPROM read sequence(s) are only performed by LAN device(s) that are enabled. The following
illustration more clearly illustrates the EEPROM read sequence for a scenario where a single LAN
device is enabled:
12.4 Shared FLASH
The Ethernet controller provides an interface to an external FLASH/ROM memory device, as
described in Section 7. This FLASH/ROM device can be mapped into memory and/or I/O address
space for each LAN device through the use of PCI Base Address Registers (BARs). Bit 3 of the
EEPROM Initialization Control Word 3 associated with each LAN device selectively disables/
enables whether the FLASH can be mapped for each LAN device by controlling the BAR register
advertisement and writeability.
12.4.1 FLASH Access Contention
Unlike the shared EEPROM implementation, the Ethernet controller does NOT implement any
internal arbitration between FLASH accesses initiated through the LAN A device and those
initiated through the LAN B device. If accesses from both LAN devices are initiated during the
same approximate time window, access contention can occur. If contention occurs, the external
FLASH addresses can be corrupted or unstable throughout the access. During writes to FLASH,
contention can result in corrupt or unstable data values; contention during reads can result in
erroneous read data being returned.
EEPROM read,
LAN
A device
9
Running
3
t
eepci
t
ee
6
5
3
t
clkpr
t
pgrst
t
pree
EEPROM read,
LAN
EEPROM read,
LAN
A device
B device
EEPROM read,
LAN
A device
2
t
ee
t
pgee
PCI Pins
Reading EEPROM
RST#
CLK
125 MHz XTAL IN
t
txpg
t
ppg
1
Power
LAN_PWR_GOOD