Multiple Descriptor-Queues

1
Multiple Descriptor-Queues

• We discover the role played by the MULR-bit (bit
  18) in the Transmit Control Register

2
Our igbe.c tool

• We wrote this module as an aid for doing
  debugging of our device-driver routines
• It creates a pseudo-file that will show us the
  current values in significant registers
• Already it has disclosed a problem with our
  previous txburst.c demonstation
• Driver wrote 0x0103F0F8 into TCTL, but
  /proc/igbe shows 0x1103F0F8 in TCTL

3
Screenshot
4
Transmit Control (0x0400)
31 30 29 28 27 26
25 24 23 22 21
20 19 18 17 16
R 0
R 0
R 0
MULR
TXCSCMT
UNO RTX
RTLC
R 0
SW XOFF
COLD (upper 6-bits) (COLLISION DISTANCE)
15 14 13 12 11
10 9 8 7 6 5
4 3 2 1 0
COLD (lower 4-bits) (COLLISION DISTANCE)
0
ASDV
I L O S
S L U
TBI mode
P S P
0 0
R 0
R 0
E N
SPEED
CT (COLLISION THRESHOLD)
EN Transmit Enable SWXOFF Software XOFF
Transmission PSP Pad Short Packets RLTC
Retransmit on Late Collision CT Collision
Threshold (0xF) UNORTX Underrun No
Re-Transmit COLD Collision Distance
(0x3F) TXCSCMT TxDescriptor Minimum
Threshold MULR Multiple Request Support
We used 0x0103F0F8 in TCTL to setup the transmit
engine before enabling it
82573L
5
Twin Descriptor Queues
Tx Desc Queue0
TDBA0
Tx Desc Queue1
TDBA1
TDH1
TDH0
TDT0
TDT1
descriptor is owned by device-driver
descriptor is owned by network-controller
6
Tx Arbitration Count (0x3840)
31 30 29 28 27 26
25 24 23 22 21
20 19 18 17 16
RESERVED 0
15 14 13 12 11
10 9 8 7 6 5
4 3 2 1 0
RESERVED 0
0
RATIO
I L O S
S L U
TBI mode
0 0
COUNT (must not be 0)
R 0
E N A B L E
ENABLE Descriptor Enable (Always set
to1) RATIO Compensation
Ratio (001/1, 011/2, 101/4, 111/8)
82573L