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Network Device Drivers

Dr A Sahu

Dept of Comp Sc & Engg.

IIT Guwahati

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Outline

  • PCI Devices
  • NIC Cards
    • Specific to 82573 (Intel NIC)
    • How transmit works
    • How receive work
  • Network Device Driver

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PCI Configuration Header

Status

Register

Command

Register

Device

ID

Vendor

ID

BIST

Cache

Line

Size

Class Code

Class/SubClass/ProgIF

Revision

ID

Base Address 0

Subsystem

Device ID

Subsystem

Vendor ID

CardBus CIS Pointer

reserved

capabilities

pointer

Expansion ROM Base Address

Minimum

Grant

Interrupt

Pin

reserved

Latency

Timer

Header

Type

Base Address 1

Base Address 2

Base Address 3

Base Address 4

Base Address 5

Interrupt

Line

Maximum

Latency

31 0

31 0

16 doublewords

Dwords

1 - 0

3 - 2

5 - 4

7 - 6

9 - 8

11 - 10

13 - 12

15 - 14

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Three IA-32 address-spaces

​

memory

space

(4GB)

​

i/o space

(64KB)

PCI

configuration

space

(16MB)

accessed using a large variety of processor

instructions (mov, add, or, shr, push, etc.)

and virtual-to-physical address-translation

accessed only by using the processor’s

special ‘in’ and ‘out’ instructions

(without any translation of port-addresses)

i/o-ports 0x0CF8-0x0CFF dedicated to accessing PCI Configuration Space

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Interface to PCI Configuration Space

reserved

CONFADD

( 0x0CF8)

CONFDAT

( 0x0CFC)

31 23 16 15 11 10 8 7 2 0

E

N

bus

(8-bits)

device

(5-bits)

doubleword

(6-bits)

function

(3-bits)

00

PCI Configuration Space Address Port (32-bits)

PCI Configuration Space Data Port (32-bits)

31 0

Enable Configuration Space Mapping (1=yes, 0=no)

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Reading PCI Configuration Data

  • Step one: Output the desired longword’s address (bus, device, function, and dword) with bit 31 set to 1 (to enable access) to the Configuration-Space Address-Port
  • Step two: Read the designated data from the Configuration-Space Data-Port
  • Already discussed PCI-probes pciprobes.c
    • Lect 29..Showing vram, pciprobe.cpp

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How ‘transmit’ works

descriptor0

descriptor1

descriptor2

descriptor3

0

0

0

0

Buffer0

Buffer1

Buffer2

Buffer3

List of Buffer-Descriptors

We setup each data-packets that we want to be transmitted in a ‘Buffer’ area in ram

We also create a list of buffer-descriptors and inform the NIC of its location and size

​

Then, when ready, we tell the NIC to ‘Go!’ (i.e., start transmitting), but let us know when these transmissions are ‘Done’

Random Access Memory

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Registers’ Names

  • Memory-information registers
    • TDBA(L/H) = Transmit-Descriptor Base-Address Low/High (64-bits)
    • TDLEN = Transmit-Descriptor array Length
    • TDH = Transmit-Descriptor Head
    • TDT = Transmit-Descriptor Tail
  • Transmit-engine control registers
    • TXDCTL = Transmit-Descriptor Control Register
    • TCTL = Transmit Control Register
  • Notification timing registers
    • TIDV = Transmit Interrupt Delay Value
    • TADV = Transmit-interrupt Absolute Delay Value

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Tx-Desc Ring-Buffer

Circular buffer (128-bytes minimum)

TDBA

base-address

TDLEN

(in bytes)

TDH (head)

TDT (tail)

= owned by hardware (nic)

= owned by software (cpu)

0x00

​

0x10

​

0x20

​

0x30

​

0x40

​

0x50

​

0x60

​

0x70

​

0x80

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Tx-Descriptor Control (0x3828)

0

0

0

0

0

0

0

G

R

A

N

0

0

WTHRESH

(Writeback Threshold)

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

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

0

0

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16

PTHRESH

(Prefetch Threshold)

0

0

Recommended for 82573: 0x01010000 (GRAN=1, WTHRESH=1)

“This register controls the fetching and write back of transmit 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 (0=cache lines, 1=descriptors). When GRAN = 1,

all descriptors are written back (even if not requested).” --Intel manual

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Transmit Control (0x0400)

R

=0

R

=0

R

=0

MULR

TXCSCMT

UNO

RTX

RTLC

R

=0

SW

XOFF

COLD (upper 6-bits)

(COLLISION DISTANCE)

COLD (lower 4-bits)

(COLLISION DISTANCE)

0

ASDV

I

L

O

S

S

L

U

TBI

mode

P

S

P

0 0

R

=0

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

R

=0

E

N

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16

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

82573L

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Tx Configuration Word (0x0178)

82573L

ANE

Tx

Config

ITCE

R

=0

IAME

R

=0

DF

PAR

EN

PB

PAR

EN

Tx

LS

Tx

LS

Flow

=0

R

=0

Phy

Pwr

Down

En

DMA

Dyn

GE

R

=0

RO

DIS

Reserved

(=0)

SPD

BYPS

R

=0

EE

RST

ASD

CHK

R

=0

R

=0

R

=0

R

=0

R

=0

R

=0

R

=0

R

=0

0 0

TxConfigWord

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16

ANE = Auto-Negotiation Enable

TxConfig = Transmit Configuration Control bit

TxConfigWord = Transmit Configuration Word

This register has two meanings, depending on the state of the ANE bit

(i.e., setting ANE=1 enables the hardware auto-negotiation machine).

Applicable only in SerDes mode; program as 0 for internal-PHY mode.

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TxDesc Command-field

IDE

VLE

DEXT

reserved

=0

RS

IC

IFCS

EOP

7 6 5 4 3 2 1 0

EOP = End Of Packet (1=yes, 0=no)

IFCS = Insert Frame CheckSum (1=yes, 0=no) – provided EOP is set

IC = Insert CheckSum (1=yes, 0=no) as indicated by CSO/CSS fields

RS = Report Status (1=yes, 0=no)

DEXT = Descriptor Extension (1=yes, 0=no) use ‘0’ for Legacy-Mode

VLE = VLAN-Packet Enable (1=yes, 0=no) – provided EOP is set

IDE = Interrupt-Delay Enable (1=yes, 0=no)

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TxDesc Status field

reserved

=0

LC

EC

DD

3 2 1 0

DD = Descriptor Done

this bit is written back after the NIC processes the descriptor

provided the descriptor’s RS-bit was set (i.e., Report Status)

EC = Excess Collisions

indicates that the packet has experienced more than the

maximum number of excessive collisions (as defined by

the TCTL.CT field) and therefore was not transmitted.

(This bit is meaningful only in HALF-DUPLEX mode.)

LC = Late Collision

indicates that Late Collision has occurred while operating in

HALF-DUPLEX mode. Note that the collision window size

is dependent on the SPEED: 64-bytes for 10/100-MBps, or

512-bytes for 1000-Mbps.

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0

Device Status (0x0008)

?

0

0

0

0

0

0

0

0

0

0

0

GIO

Master

EN

0

0

0

0

0

0

0

PHY

reset

ASDV

I

L

O

S

S

L

U

0

TX

OFF

0 0

F

D

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Function

ID

L

U

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16

SPEED

FD = Full-Duplex

LU = Link Up

TXOFF = Transmission Paused

SPEED (00=10Mbps,01=100Mbps, 10=1000Mbps, 11=reserved)

ASDV = Auto-negotiation Speed Detection Value

82573L

some undocumented functionality?

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Device Control (0x0000)

PHY

RST

VME

R

=0

TFCE

RFCE

RST

R

=0

R

=0

R

=0

R

=0

R

=0

ADV

D3

WUC

R

=0

D/UD

status

R

=0

R

=0

R

=0

R

=0

R

=0

FRC

DPLX

FRC

SPD

R

=0

SPEED

R

=0

S

L

U

R

=0

R

=0

R

=1

0 0

F

D

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

GIO

M

D

R

=0

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16

FD = Full-Duplex SPEED (00=10Mbps, 01=100Mbps, 10=1000Mbps, 11=reserved)

GIOMD = GIO Master Disable ADVD3WUP = Advertise Cold Wake Up Capability

SLU = Set Link Up D/UD = Dock/Undock status RFCE = Rx Flow-Control Enable

FRCSPD = Force Speed RST = Device Reset TFCE = Tx Flow-Control Enable

FRCDPLX = Force Duplex PHYRST = Phy Reset VME = VLAN Mode Enable

82573L

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Ethernet packet layout

  • Total size normally can vary from 64 bytes up to 1536 bytes (unless ‘jumbo’ packets and/or ‘undersized’ packets are enabled)
  • The NIC expects a 14-byte packet ‘header’ and it appends a 4-byte CRC check-sum

the packet’s data ‘payload’ goes here

(usually varies from 56 to 1500 bytes)

destination MAC address

(6-bytes)

source MAC address

(6-bytes)

Type/length

(2-bytes)

Cyclic Redundancy

Checksum (4-bytes)

0 6 12 14

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How ‘receive’ works

descriptor0

descriptor1

descriptor2

descriptor3

0

0

0

0

Buffer0

Buffer1

Buffer2

Buffer3

List of Buffer-Descriptors

We setup memory-buffers where we want received packets to be placed by the NIC

​

We also create a list of buffer-descriptors and inform the NIC of its location and size

Then, when ready, we tell the NIC to ‘Go!’ (i.e., start receiving), but to let us know when these receptions have occurred

Random Access Memory

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Receive Control (0x0100)

R

=0

0

0

FLXBUF

SE

CRC

BSEX

R

=0

PMCF

DPF

R

=0

CFI

CFI

EN

VFE

BSIZE

B

A

M

R

=0

MO

DTYP

RDMTS

I

L

O

S

S

L

U

LPE

UPE

0 0

R

=0

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

SBP

E

N

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16

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 En BAM = Broadcast Accept Mode BSEX = Buffer Size Extension

MPE = Multicast Promiscuous En BSIZE = Receive Buffer Size SECRC = Strip Ethernet CRC

LPE = Long Packet reception Ena 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 Indic

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Registers’ Names

  • Memory-information registers
    • RDBA(L/H) = Receive-Descriptor Base-Address Low/High (64-bits)
    • RDLEN = Receive-Descriptor array Length
    • RDH = Receive-Descriptor Head
    • RDT = Receive-Descriptor Tail
  • Receive-engine control registers
    • RXDCTL = Receive-Descriptor Control Register
    • RCTL = Receive Control Register
  • Notification timing registers
    • RDTR = Receive-interrupt packet Delay Timer
    • RADV = Receive-interrupt Absolute Delay Value

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Rx-Desc Ring-Buffer

Circular buffer (128-bytes minimum)

RDBA

base-address

RDLEN

(in bytes)

RDH (head)

RDT (tail)

= owned by hardware (nic)

= owned by software (cpu)

0x00

​

0x10

​

0x20

​

0x30

​

0x40

​

0x50

​

0x60

​

0x70

​

0x80

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Rx-Descriptor Control (0x2828)

R

=0

R

=0

R

=0

R

=0

R

=0

R

=0

R

=0

G

R

A

N

R

=0

R

=0

​

1

---------

​

0

ADV

D3

WUC

SDP1

DATA

---------

​

0

SDP0

DATA

---------

D/UD

status

0

WTHRESH

(Writeback Threshold)

R

=0

R

=0

0

FRC

DPLX

FRC

SPD

0

HTHRESH

(Host Threshold)

R

=0

R

=0

A

S

D

E

0

L

R

S

T

0 0

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

0

0

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16

PTHRESH

(Prefetch Threshold)

GRAN (Granularity): 1=descriptor-size, 0=cacheline-size

Prefetch Threshold – A prefetch operation is considered when the number of valid, but unprocessed, receive descriptors that the ethernet controller has in its on-chip buffer drops below this threshold.

Host Threshold - A prefetch occurs if at least this many valid descriptors are available in host memory

Writeback Threshold - This field controls the writing back to host memory of already processed receive descriptors in the ethernet controller’s on-chip buffer which are ready to be written back to host memory

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RxDesc Status-field

PIF

IPCS

TCPCS

VP

IXSM

EOP

DD

7 6 5 4 3 2 1 0

DD = Descriptor Done (1=yes, 0=no) shows if nic is finished with descriptor

EOP = End Of Packet (1=yes, 0=no) shows if this packet is logically last

IXSM = Ignore Checksum Indications (1=yes, 0=no)

VP = VLAN Packet match (1=yes, 0=no)

USPCS = UDP Checksum calculated in packet (1=yes, 0=no)

TCPCS = TCP Checksum calculated in packet (1=yes, 0=no)

IPCS = IPv4 Checksum calculated on packet (1=yes, 0=no)

PIF = Passed In-exact Filter (1=yes, 0=no) shows if software must check

UDPCS

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RxDesc Error-field

RXE

IPE

TCPE

reserved

=0

SE

CE

7 6 5 4 3 2 1 0

RXE = Received-data Error (1=yes, 0=no)

IPE = IPv4-checksum error

TCPE = TCP/UDP checksum error (1=yes, 0=no)

SEQ = Sequence error (1=yes, 0=no)

SE = Symbol Error (1=yes, 0=no)

CE = CRC Error or alignment error (1=yes, 0=no)

SEQ

reserved

=0

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Statistics registers

  • The 82573L has several dozen statistical counters which automatically operate to keep track of significant events affecting the ethernet controller’s performance
  • Most are 32-bit ‘read-only’ registers, and they are automatically cleared when read
  • Your module’s initialization routine could read them all (to start counting from zero)

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Initializing the nic’s counters

  • The statistical counters all have address- offsets in the range 0x04000 – 0x04FFF
  • You can use a very simple program-loop to ‘clear’ each of these read-only registers

// Here ‘io’ is the virtual base-address

// of the nic’s i/o-memory region

{

int r;

// clear all of the Pro/1000 controller’s statistical counters

for (r = 0x4000; r < 0x4FFF; r += 4) ioread32( io + r );

}

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A few ‘counter’ examples

0x4000 CRCERRS CRC Errors Count

0x400C RXERRC Receive Error Count

0x4014 SCC Single Collision Count

0x4018 ECOL Excessive Collision Count

0x4074 GPRC Good Packets Received

0x4078 BPRC Broadcast Packets Received

0x407C MPRC Multicast Packets Received

0x40D0 TPR Total Packets Received

0x40D4 TPT Total Packets Transmitted

0x40F0 MPTC Multicast Packets Transmitted

0x40F4 BPTC Broadcast Packets Transmitted

​

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A ‘nic.c’ character driver?

open

read

write

my_fops

ioctl

my_ioctl()

my_open()

my_read()

my_write()

my_release()

my_isr()

module_init()

module_exit()

release

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Network drivers

  • Network interface driver similar to mounted block devices
  • A Special block devices registers its disk and methods with kernel and Transmit and Receive block on request
  • Socket Read/Write system call
  • Network driver receive Asyn packet from Outside world
  • Ask to push incoming packet towards kernel

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Network drivers

  • Many administrative works
    • Setting up address, modify transmission param, maintaining traffic, error statistics
  • Network subsystem completely protocol independent
    • Software (IP) and Hardware (Eth, Ring)

​

​

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Snull: the network interface driver

  • Linux loop back driver
  • At drivers/net/loopback.c
  • It simulates conversations with real remote hosts in order to demonstrate the task of writing network drivers

​

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Assigning IP number

  • Suppose two interfaces in system sn0, sn1 interfaces
  • Loopback: it really don’t send/simulate
  • But to send actually: toggle LSBit of third octet of both src & dest address
    • It changes both the network number and host number of class C IP number
    • The net effect is packet sent to network interface sn0 appears on sn1
  • Snullnet0: network connected to sn0 interface, Snullnet1:network connected to sn1 interface
    • Must have 24 bit masks
  • local0, local1: IP address assigned: must differs in the Lsbit of their in 3rd and 4th octet

​

​

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The physical transport of Packets

  • Snull interface correspond to Ethernet class
  • It emulates Ethernet
  • Kernel offers some generalized support of Ethernet devices
  • Ethernet is strong: plip (interface used for printer): declares itself as Ethernet device
  • Watch packets: tcpump
  • Snull works only wit IP Packets
    • Modify src,dst,chksu in the IP headers: without checking wheather it actually conve IP infos

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Connecting to kernel: Device Registration

  • Loopback.c, plip.c, e100.c are examples of network drivers : /drivers/net/
  • Device registration:
    • Alloc net devices (Request for resources and offer facilities)
      • Struct net_devices *snull_dev[2] ; //linux/netdevice.h
      • snull_dev[0]=alloc_netdev(sizeof(struct snull_priv), “sn%d”,snull_init);
      • Alloac_etherdev(int sizeof_priv); /wrapper to alloc_netdev
    • After initialization complete register the devices
      • register_netdev(snull_dev[i]); // return 1 if fails

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  • Snull uses alloc_netdev, it have a separate initialization function
  • Ether_setup(dev);//it assign some field
    • dev->open=snull_open;
    • dev->close=snull_release;
    • set_config, hard_start_txmit, do_ioctl, get_stats, rebuild_header, tx_timeout, watchdog_timeo,
    • flag|=IFFNOARP;
    • Features|=NETIF_F_NO_CSUM
    • hard_header_cache=NULL//disable caching
  • Private data pointers: priv with al netdevices

Connecting to kernel: Device initialization

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Private data

  • Strcut snull_priv *priv=nedev_priv(dev);

Strcu snull_priv {

struct net_devices_stats stats;

int status;

strcut snull_packet *ppool;

struct snul_packet *rx_queue;

int rx_enabled, tc_packele;

u8 *tx_packetdata;

struct sk_bff *skb;

spinlock_t lock;

};

  • Initialization

priv=netdriv_priv(dev);

memset(priv,0,sizeof(strcutn null_priv));

spin_lock_init(&priv->lock);

snull_rx_inits(dev,1); //enable revice interrupts

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  • Cleanup (snull_dev[i]){

unregister_netdev(snull_dev[i]);

snull_teardown_pool(snull_dev[i]);

free_netdev(snull_dev[i]);

}

  • Tearown_pool: flush packet pool and bufffer of private data

​

Connecting to kernel: Module unloading

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Net_device Strcutures

  • Global Information
    • name: name of device
    • State: state of device
    • net_device *next; // ptr to next dev in global list
    • init_funtion: An init fun called by reg_netdev();
  • Hardware Information
  • Interface Information
  • Device methods

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Net_device Strcutures: Hardware info

  • Low level hardware information
  • Base_address: io_base address of network interface
  • Char irq: dev->irq, the assigned interrupt number..ifconfig
  • Char if_port: the port is in use on multiport device..10base
  • Char dma; // dma allcoated by the device for ISA bus
  • Device memory information: address of shared memory used by the devices
    • Rmem (rx mem) , mem (tx_mem)
    • rmem_start, rmem_end, mem-start, mem_end;

​

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Net_device: Interface information

  • Init setup most of the information But device specific setup information need to setup later on
  • Non ethernet interface can use helper functions
    • fc_setup, ltalk_setup, fddi_setup
    • Fiber channel, local talk, fiber dis data ineterface, token ring, hihh perf parllel interface (hppi_setup)
  • Non default interface filed
    • Hard_headerlen,MTU (max tx unit=1500 oct ), tx_queue_len (ether=1000, pipl=10), short type, char adresslen; char dev_addeess[Max_add_len], breadcast[max_ad_len]
  • Flags bt sets: Mask bits, loopback, debug, noarp, multicast
  • Special hardware capability the device has: DMA

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Net_device: Device methods

  • Fundamental method
    • Open, Stop, Hard_start_xmit
    • Hard_header, Rebuild_header
    • Tx_timeout, Net_device_stats, Set_config
  • Optional methods
    • Poll, poll_controller, do_ioctl, set_multicastlist
    • Set_mac_address,change_mtu, header_cache, header_cache_update, hard_header_parse
  • Utilities fileds (not methods)
    • Trans_start, last_rx, watchdog_timeo, *priv, mc_list, mc_count, xmit_lock, xmit_lock_owner

​

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Open() & Close ()

int snull_open(struct net_device *dev) {

/* request_region( ), request_irq( ), Assign the hardware address of the board: use "\0SNULx", where

* x is 0 or 1. The first byte is '\0' to avoid being a multicast

* address (the first byte of multicast addrs is odd). */

memcpy(dev->dev_addr, "\0SNUL0", ETH_ALEN);

if (dev = = snull_devs[1])

dev->dev_addr[ETH_ALEN-1]++; /* \0SNUL1 */

netif_start_queue(dev);

return 0;

}

​

int snull_release(struct net_device *dev) {

/* release ports, irq and such -- like fops->close */

netif_stop_queue(dev); /* can't transmit any more */

return 0;

}

​

​

​

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Tx()

int snull_tx(struct sk_buff *skb, struct net_device *dev){

int len; char *data, shortpkt[ETH_ZLEN];

struct snull_priv *priv = netdev_priv(dev);

data = skb->data; len = skb->len;

if (len < ETH_ZLEN) {

memset(shortpkt, 0, ETH_ZLEN);

memcpy(shortpkt, skb->data, skb->len);

len = ETH_ZLEN;

data = shortpkt;

}

dev->trans_start = jiffies; /* save the timestamp */

/* Remember the skb, so we can free it at interrupt time */

priv->skb = skb;

/* actual deliver of data is device-specific, and not shown here */

snull_hw_tx(data, len, dev); return 0;

}

​

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Rx()

void snull_rx(struct net_device *dev, struct snull_packet *pkt) {

struct sk_buff *skb; struct snull_priv *priv = netdev_priv(dev);

/* * The packet has been retrieved from the transmission * medium. Build an skb around it, so upper layers can handle it */

skb = dev_alloc_skb(pkt->datalen + 2);

if (!skb) {

if (printk_ratelimit( ))

printk(KERN_NOTICE "snull rx: low on mem - packet dropped\n");

priv->stats.rx_dropped++;

goto out;

}

memcpy(skb_put(skb, pkt->datalen), pkt->data, pkt->datalen);

/* Write metadata, and then pass to the receive level */

skb->dev = dev;

skb- >protocol = eth_type_trans(skb, dev);

skb->ip_summed = CHECKSUM_UNNECESSARY; /* don't check it */

priv->stats.rx_packets++;

priv->stats.rx_bytes += pkt->datalen;

netif_rx(skb);

out: return; }

​

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Thanks�Ref: Chap 17, LDD 3e Rubini- Corbet