Linux usb2ether

1

Linux USB to
Ethernet development

spec. overview
kernel backend
driver interfaces

Copyright © 2009 by Tom J.P.Sun All rights reserved.

2

USB Overview(1)
USB 1.1/2.0 Spec. For S/W engineer:
Chap 5 “USB Data Flow Model”
Chap 9 “USB Device Framework”
Chap 10 “USB Host : H/W and S/W”

client function
S/W Logical
connection
USB USB
system device

Physical
H/W USB Bus USB Bus connection
interface interface
USB cable


3

USB Overview(2)

client

USB system

Usbcore (bus driver)

HC driver
USB device F/W
UHCI or OHCI
USB device H/W
USB bus
HC H/W SIE


4

USB communication flow

Communication
Client S/W, driver
flow

buffers

pipes

Interface
End points
USB logical device


5

USB transfer types
Control Transfer
device enumeration use this type ( issued by USBD
(bus driver))
client driver can use it ( same concept as “IOCTL”)
for “device specific commands”
Bulk Transfer
reliable, but not realtime scanner,printer
Isochronous Transfer
near realtime, but not reliable usbcam
Interrupt Transfer
reliable, realtime, but limit in bandwidth mouse
Important Concept
cncpt
USB is MasterSlave model
USBOnTheGo is peertopeer model


6

USB Descriptor Hierarchy

device descriptor

Configuration
Configuration
2
1

Interface 0 Interface 1 Interface 1 Interface 0 Interface 1
AS0 AS0 AS1 AS1 AS0

Endpoint Endpoint Endpoint More endpoint
1 2 3 descriptors


7

USB device request


8

USB standard commands
(bRequest value)
GET_STATUS 0
CLEAR_FEATURE 1
Reserved for future use 2
SET_FEATURE 3
Reserved for future use 4
SET_ADDRESS 5
GET_DESCRIPTOR 6
SET_DESCRIPTOR 7
GET_CONFIGURATION 8
SET_CONFIGURATION 9
GET_INTERFACE 10
SET_INTERFACE 11
SYNCH_FRAME 12


9

9620 vendor commands
(bRequest value)
DM_READ_REGS 0
DM_WRITE_REGS 1
DM_READ_MEMS 2
DM_WRITE_REG 3
DM_WRITE_MEMS 5
DM_WRITE_MEM 7


10

Configure Device
When USB Device Plugged in, USBD + driver
should complete the device enumeration steps
1 get dev descriptor
dev descriptor
2 set address

3 get dev descriptor
Host dev descriptor Device

4 set cfg

5 set itf

1 2 done by USBD
CATC can see these transfers...
3 4 5 done by client

11

USB Core API Layers

USB device USB device USB device
driver driver driver

upper
API
USBD = USB core ( usb.c )
lower
API

USB UHCI USB OHCI other USB
driver driver HC driver

ready


12

USB

spec. overview
kernel backend
driver interfaces


13

USB driver structure(1)
struct usb_driver {
const char *name;
void* (*probe) (
struct usb_interface *
const struct usb_device_id *id_table);
void (*disconnect)
(struct usb_device *, void *);
...
const struct usb_device_id *id_table;
struct device_driver driver;
};

@name: module name
@probe: called to see if the driver will handle this USB interface , if
it is, return zero, otherwise return a negative error code.
@disconnect: called when the interface is no longer accessible.
@id_table: USB use this table to support hotplugging, export this
id_table with MODULE_DEVICE_TABLE( ) macro.
@driver: driver modle core driver structure


14

USB driver structure(2)
On device attachment,
USB framework walk USBD
through the id_table

usb_register( )
First enter point on
device match
usb_driver

my_probe( )
…
my_disconnect( )
…
id_table : match list
1st match dev
2nd match dev
… On device detachment,
USB framework call this.


15

Standard Commands
USBD provides USB standard
commands
usb_set_configuration( struct usb_device* dev, int cfg);
usb_set_interface(struct usb_device*, int itf, int alt);
usb_get_descriptor(…);
usb_get_string(…);
usb_get_status(…);

kenrel_source/drivers/usb/core/message.c


16

The USB data path
Can isolate driver,
when proving h/w
App App
Linux O.S. Interface

Network
FS
(TCP/IP)
App open the usb device
interface, direct transfer
data to the USB HC
In PCI USB
Kernel subsystem subsystem App open socket,
data transferred by
Network and USB
PCI USB driver
driver driver
H/W

EtherNet PCI USB EtherNet
Chip bus HC Chip


17

The usbnet minidriver
The mini-driver interface
...
Network tx_fixup( )
(TCP/IP) rx_fixup( )
... asix

usbnet dm9601
driver
framework
...other
The usbnet module manages:
client
drivers
1. skb flow control with the Network layer
2. urb flow control with the USB bus driver
The mini-driver only take simple work
for device-specific fixups.
so, the performance issue should be little
between each mini-driver, (Yes !
performance depends major on the H/W)


18

USB

spec. overview
kernel backend
driver interfaces


19

dm9601_rx_fixup( )
Object: correct the contents of skb ( data for
the network layer ), which is device specific.
e.g. dm9620 h/w give us data with length in
the first 2 bytes, rx_fixup( ) should remove it
before passing to the network layer
Mini-driver interface
static const struct driver_info dm9601_info = {
.description = "Davicom DM9601 USB Ethernet",
.flags = FLAG_ETHER,
.bind = dm9601_bind,
.rx_fixup = dm9601_rx_fixup,
.tx_fixup = dm9601_tx_fixup,
.status = dm9601_status,
.link_reset = dm9601_link_reset,
.reset = dm9601_link_reset,
};


20

dm9601_tx_fixup( )
Object: correct the contents of skb ( data for
the network layer ), which is device specific.
e.g. dm9620 h/w need data with length in
the first 2 bytes, tx_fixup( ) should add it
before passing to the chip

static const struct driver_info dm9601_info = {
.description = "Davicom DM9601 USB Ethernet",
.flags = FLAG_ETHER,
.bind = dm9601_bind,
.rx_fixup = dm9601_rx_fixup,
.tx_fixup = dm9601_tx_fixup,
.status = dm9601_status,
.link_reset = dm9601_link_reset,
.reset = dm9601_link_reset,
};


21

vendor commands(1)
static int dm_read(struct usbnet *dev, u8 reg, u16 length, void *data)
{
devdbg(dev, "dm_read() reg=0x%02x length=%d", reg, length);
return usb_control_msg(dev->udev,
usb_rcvctrlpipe(dev->udev, 0),
DM_READ_REGS,
USB_DIR_IN | USB_TYPE_VENDOR |
USB_RECIP_DEVICE,
0, reg, data, length,
USB_CTRL_SET_TIMEOUT);
}


22

vendor commands (2)
static int dm_write(struct usbnet *dev, u8 reg, u16 length, void *data)
{

return usb_control_msg(dev->udev,
usb_sndctrlpipe(dev->udev, 0),
DM_WRITE_REGS,
USB_DIR_OUT | USB_TYPE_VENDOR |
USB_RECIP_DEVICE,
0, reg, data, length,
USB_CTRL_SET_TIMEOUT);
}

Concept: The vendor commands are used to setup h/w , while
the real data are transferred by b-in , b-out pipes,
not the control pipe.


23

Device ID & Vendor ID

u
s
e Use this information to
load driver when plug-in...


24

Appendix : libusb
Bypass driver, direct call via the
USB subsystem.
Package 0.1.12 (simple, but not well
support thread )
we need header files:
#> apt-get src libusb-dev
(get libusb-0.1.12 under the same directory)

Makefile:
usbtest: usbtest.c
gcc -g -Wall $< -o $@ -I./libusb-0.1.12 -lusb

( assume usbtest.c is the our test program using the
libusb , use root to test...)


25

Example usage of libusb (1)
Include headers:

#include "linux.h"
#include "usbi.h"

Initial setup provided by libusb

usb_init();
usb_find_busses();
usb_find_devices();


26

Get our device:

for (usb_bus = usb_busses;
usb_bus;
usb_bus = usb_bus->next) {
for (dev = usb_bus->devices;
dev;
dev = dev->next) {
if ((dev->descriptor.idVendor
== VENDOR_ID) &&
(dev->descriptor.idProduct
== PRODUCT_ID))
return dev;
}
}


27

Open:

usb_handle = usb_open(usb_dev);

B-out:

mk_raw(buf, SZBUF); /* prepare data in buf*/
retval = usb_bulk_write(usb_handle, ep_bulk_out,
(char*)buf, SZBUF, 5000);

B-in:

memset(buf, 0, SZBUF);
retval = usb_bulk_read(usb_handle, ep_bulk_in,
(char*)buf, SZBUF, 5000);


28

Control pipe:
usb_control_msg(handle, 0x000000c0, DM_READ_REGS,
0,0xff & reg,data,length,5000);

prototype: libusb-0.1.12/linux.c
int usb_control_msg(
usb_dev_handle *dev,
int requesttype,
int request,
int value,
int index,
char *bytes,
int size,
int timeout);


29

The End


Linux usb2ether

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