Our nic.c module

1
Our nic.c module

• We create a character-mode device-driver for
  the 82573L NIC to use in futrure experiments

2
Character devices

• The concept of a character mode device is that
  it provides a stream of data bytes which
  application-programs can access with these
  standard Linux system-calls
• open() and close()
• read() and write()
• lseek()

3
Requirement

• The character-mode devices are known to a Linux
  system by their names and by an associated pair
  of ID-numbers (major and minor) normally set up
  by a superuser
• root mknod /dev/nic c 97 0
• root chmod arw /dev/nic

4
Driver module
nic.c
this modules collection of payload
functions
get_info()
read()
isr()
write()
ioctl()
character-mode device-drivers
required file-operations data-structure
fops
required pair of module administration
functions
module_init
module_exit
5
Overview
user space kernel
space
Linux operating system Kernel
standard runtime libraries
networking subsystem
file subsystem
char driver module
application program
hardware
6
Transmit operation
user space
kernel space
Linux OS kernel
runtime library
file subsystem
nic device-driver
write()
my_write()
application program
packet buffer
user data-buffer
copy_from_user()
DMA
hardware
7
Receive operation
user space
kernel space
Linux OS kernel
runtime library
file subsystem
nic device-driver
read()
my_read()
application program
packet buffer
user data-buffer
copy_to_user()
DMA
hardware
8
Our packet-format

• Our nic.c driver elects to have the NIC append
  padding to any short packets
• But this prevents a receiver from knowing how
  many bytes represent actual data
• To solve this problem, we added our own count
  field to each packets payload

0 6
12
14
actual bytes of user-data
destination MAC-address
source MAC-address
Type/Len
count
9
Using echo and cat

• Our device-driver module nic.c is intended to
  allow two programs that are running on a pair of
  anchor-cluster PCs to communicate via that
  clusters Local Area Network

Receiving
Transmitting
echo Hello gt /dev/nic _
cat /dev/nic Hello _
10
Jumbo packets

• One of the innovations provided by gigabit
  ethernet technology is support in the NIC for
  larger-than-normal size data-packets
• The most common upper bound for data capacity in
  jumbo frames is 9000 bytes (plus the usual
  ethernet frame header)
• Our 82573L network controller implements long
  packet support as an option

11
Receive Control (0x0100)
31 30 29 28 27 26
25 24 23 22 21
20 19 18 17 16
R 0
0
0
FLXBUF
SE CRC
BSEX
R 0
PMCF
DPF
R 0
CFI
CFI EN
VFE
BSIZE
15 14 13 12 11
10 9 8 7 6 5
4 3 2 1 0
B A M
R 0
MO
DTYP
RDMTS
I L O S
S L U
LPE
UPE
0 0
R 0
SBP
E N
LBM
MPE
EN Receive Enable DTYP Descriptor
Type DPF Discard Pause Frames SBP Store Bad
Packets MO Multicast Offset PMCF Pass MAC
Control Frames UPE Unicast Promiscuous Enable
BAM Broadcast Accept Mode BSEX Buffer Size
Extension MPE Multicast Promiscuous Enable
BSIZE Receive Buffer Size SECRC Strip
Ethernet CRC LPE Long Packet reception Enable
VFE VLAN Filter Enable FLXBUF Flexible
Buffer size LBM Loopback Mode CFIEN
Canonical Form Indicator Enable RDMTS
Rx-Descriptor Minimum Threshold Size CFI
Cannonical Form Indicator bit-value
Our nic.c driver initially will program this
register with the value 0x0400801C. Later, when
everything is ready, it will turn on bit 1 to
start the receive engine
82573L
12
Project 1

• Revise our nic.c device-driver module so it
  will allow application programs to write (i.e.,
  transmit) and to read (i.e., receive) jumbo
  packets which contain up to 9000 data-bytes, plus
  ethernet header and CRC
• Construct a pair of application-programs that you
  can use (in place of echo and cat) to test
  your enhanced device-driver

13
In-class demonstration

• We can use our (unmodified) nic.c driver to
  study the way in which our 82573L NIC uses a
  portion of its internal i/o-memory
• We can view the NICs internal memory using our
  82573.c character driver and our fileview
  navigation-tool
• Weve also created an additional module (named
  nicmap.c) to assist in this study

14
Rx-Descriptor Control (0x2828)
31 30 29 28 27 26
25 24 23 22 21
20 19 18 17 16
0
0
0
0
0
0
0
G R A N
0
0
WTHRESH (Writeback Threshold)
15 14 13 12 11
10 9 8 7 6 5
4 3 2 1 0
0
0
0
FRC DPLX
FRC SPD
0
HTHRESH (Host Threshold)
I L O S
0 0
A S D E
0
L R S T
0 0
0
0
PTHRESH (Prefetch Threshold)
0
0
This register controls the fetching and write
back of receive descriptors. The three
threshhold values are used to determine when
descriptors are read from, and written to, host
memory. Their values can be in units of cache
lines or of descriptors (each descriptor is 16
bytes), based on the value of the GRAN bit
(0cache lines, 1descriptors). When GRAN 1,
all descriptors are written back (even if not
requested). --Intel manual
Recommended for 82573 0x01010000 (GRAN1,
WTHRESH1)
15
Exploring RX Descriptor FIFO
Timeout for an in-class demonstration
16
In-class exercise

• Modify the code in our nicmap.c module so that
  you can use it to explore the NICs TX Descriptor
  FIFO (begins at 0x07000)