Intel 82540EP/EM Benutzerhandbuch
Receive and Transmit Description
30
Software Developer’s Manual
The diagrams below show how the Packet Timer and Absolute Timer can be used together:
3.2.7.2
Small Receive Packet Detect
A Small Receive Packet Detect interrupt (ICR.SRPD) is asserted when small-packet detection is
enabled (RSRPD is set with a non-zero value) and a packet of (size
enabled (RSRPD is set with a non-zero value) and a packet of (size
RSRPD.SIZE) has been
transferred into the host memory. When comparing the size the headers and CRC are included (if
CRC stripping is not enabled). CRC and VLAN headers are not included if they have been
stripped. A receive timer interrupt cause (ICR.RXT0) is also noted when the Small Packet Detect
interrupt occurs.
CRC stripping is not enabled). CRC and VLAN headers are not included if they have been
stripped. A receive timer interrupt cause (ICR.RXT0) is also noted when the Small Packet Detect
interrupt occurs.
For the 82541xx and 82547GI/EI, receiving a small packet does not clear the absolute or packet
delay timers, so one packet might generate two interrupts, one due to small packet reception and
one due to timer expiration.
delay timers, so one packet might generate two interrupts, one due to small packet reception and
one due to timer expiration.
A bsolute Tim er V alue
PK T #1
PK T #2
PK T #3
PK T #4
Interrupt generated due to PK T #1
A bsolute Tim er Value
PK T #1
PK T #2
PK T #3
P KT #4
Interrupt generalted (due to P KT #4)
as absolute tim er expires.
Packet delay tim er disabled untill
next packet is received and
transferred to host m em ory.
as absolute tim er expires.
Packet delay tim er disabled untill
next packet is received and
transferred to host m em ory.
P KT #5
P KT #6
...
...
...
A bsolute Tim er Value
1) Packet tim er expires
2) Interrupt generated
3) Absolute tim er reset
2) Interrupt generated
3) Absolute tim er reset
A bsolute Tim er Value
PK T #1
PK T #2
PK T #3
P KT #4
Interrupt generalted (due to P KT #4)
as absolute tim er expires.
Packet delay tim er disabled untill
next packet is received and
transferred to host m em ory.
as absolute tim er expires.
Packet delay tim er disabled untill
next packet is received and
transferred to host m em ory.
P KT #5
P KT #6
...
...
...
A bsolute Tim er Value
1) Packet tim er expires
2) Interrupt generated
3) Absolute tim er reset
2) Interrupt generated
3) Absolute tim er reset
C ase A : U sing only an absolute tim er
C ase B: U sing an absolute tim e in conjunction w ith the P acket tim er
C ase C : P acket tim er expiring w hile a packet is transferred to host m em ory .
Illustrates that packet tim er is re-started only after a packet is transferred to host m em ory.