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title:WebUSB example
keywords:linux,webusb,usb,usbmon,ch341,pl2101
# WebUSB example
## Hardware requirements
Modern browser have some cool API's like WebUSB that allows from browser
acces USB stack. Here is a steps to try it out. As internet doesnt have
any basic example of stuff how things works, here is all info needed to
make first WebUSB requests running. On most basic devices out there.
USB serail interface is cheap to get on any online shop here is quite
common chip models CH341,PL2303.
TODO
* describe how request decoded add py example code
* describe initialisation phase
* Describe how to send data on CH341
* Describe how to recieve data on CH341
* sniffed usbmon traffic desctiption
## Gathering info
Linux provides utilities to list all usb device connections.
```
lsusb
```
Output will be something like:
```
Bus 002 Device 027: ID 1bcf:0007 Sunplus Innovation Technology Inc. Optical Mouse
Bus 002 Device 026: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
```
Our PL2303 device is connected and is on a bus 2.0
When USB device is connected to bus linux logs some information. When USB
device is there in dmesg you can find out some info.
```
dmesg | tail
```
Most important part is to find device bus id in our case it is "2-1:1.0"
```
[190298.876894] usb 2-1: USB disconnect, device number 26
[190298.877195] pl2303 ttyUSB0: pl2303 converter now disconnected from ttyUSB0
[190298.877245] pl2303 2-1:1.0: device disconnected
[190301.871959] usb 2-1: new full-speed USB device number 28 using xhci_hcd
[190302.012793] usb 2-1: New USB device found, idVendor=067b, idProduct=2303, bcdDevice= 3.00
[190302.012799] usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[190302.012802] usb 2-1: Product: USB-Serial Controller
[190302.012804] usb 2-1: Manufacturer: Prolific Technology Inc.
[190302.013632] pl2303 2-1:1.0: pl2303 converter detected
[190302.014426] usb 2-1: pl2303 converter now attached to ttyUSB0
```
## Setting up udev
Use usb bus id to unbind driver. If its not done there will be no permission
error, or device busy error. Use one of lines to unbind device driver by usb
bus id.
```
echo "2-2:1.0" > /sys/bus/usb/drivers/pl2303/unbind
echo "2-2:1.0" > /sys/bus/usb/drivers/ch341/unbind
```
If you have other errors related to not able to connect to device then or no
permsision. Add file to udev rules in /etc/udev/rules.d directory
/etc/udev/rules.d/88-hello-usb.rules
Here is examples of USB ids for PL2303 and CH341
```
SUBSYSTEMS=="usb", ATTR{idVendor}=="067b", ATTR{idProduct}=="2303", MODE:="0666"
SUBSYSTEMS=="usb", ATTR{idVendor}=="1a86", ATTR{idProduct}=="7523", MODE:="0666"
```
As rulles is not loaded after file are created or new entries are added.
Need to restart udev daemon so new rulles are added to current running rulles.
```
udevadm control --reload-rules && udevadm trigger
```
## Programming
Most of modern browsers provide javascript API for accesing USB its called
WebUSB API.
### Get request to access device
First thing that is needed to do is request devices. Popup windows to select
device will appear.
```js
serial.requestPort = function() {
const filters = [
{ vendorId:0x067b, productId:0x2303 }, //cp210
{ vendorId:0x1a86, productId:0x7523 }, //ch341
];
return navigator.usb.requestDevice({ 'filters': filters }).then(
device => new serial.Port(device)
);
}
```
### Recieving data
To recieve date control request need to be created.
Request constructed according to suported protocol that may differ
from device to device.
PL2303 and CH3421 have totaly different interfeises. Steps to initialise
device also differs.
```js
serial.Port.prototype.vendorRead = function(value) {
console.log("Read val="+value);
return this.device.controlTransferIn({
'requestType': 'vendor',
'recipient': 'device',
'request':serial.VENDOR_READ_REQUEST,
'value':value,
'index':0,
},1);
};
```
### Sending data
```js
serial.Port.prototype.vendorWrite = function(value,index) {
console.log("Write idx "+index+" val = "+value)
return this.device.controlTransferOut({
'requestType': 'vendor',
'recipient': 'device',
'request': serial.VENDOR_WRITE_REQUEST,
'value': value,
'index': index,
});
};
```
### CH341 chip request table
| | |
| --- | --- |
### PL2301 chip request table
| Request name | value |
| --- | --- |
| CP210_VENDOR_WRITE_REQUEST | |
| CP210_VENDOR_READ_REQUEST | |
| CP210_GET_LINE_REQUEST | |
| CP210_SET_LINE_REQUEST | |
| CP210_SET_CONTROL_REQUEST | |
| CP210_BREAK_REQUEST | |
## Sniffing USB traffic
Linux provides infrastructure to see USB transactions. Its allow to
debug or sniff some USB trafic, so in case if there is some unknown
parts how USB initialisation is working, you have change to figure out
by seeing sequenc of commands sent to USB interface.
### Setting usbmon
```
mount -t debugfs none_debugs /sys/kernel/debug
modprobe usbmon
ls /sys/kernel/debug/usb/usbmon
```
```
T: Bus=01 Lev=04 Prnt=43 Port=03 Cnt=02 Dev#= 45 Spd=12 MxCh= 0
D: Ver= 1.10 Cls=ff(vend.) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
P: Vendor=1a86 ProdID=7523 Rev= 2.54
S: Product=USB2.0-Serial
C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr= 96mA
I:* If#= 0 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=01 Prot=02 Driver=ch341
E: Ad=82(I) Atr=02(Bulk) MxPS= 32 Ivl=0ms
E: Ad=02(O) Atr=02(Bulk) MxPS= 32 Ivl=0ms
E: Ad=81(I) Atr=03(Int.) MxPS= 8 Ivl=1ms
```
```
cat /sys/kernel/debug/usb/usbmon/1u > /tmp/1.mon.out
```
### Sniffed traffic example
## Thx
[daGrevis](https://github.com/daGrevis) - gave tips about using await/async in js
[jurgenzz](https://github.com/jurgenzz) - help solving await/async issues
[#developers.lv](https://developers.lv) - having patiens for listening to js nonsence from js-newbie
## Source
## Links
[https://www.mankier.com/8/usbmon](https://www.mankier.com/8/usbmon)
[https://www.kernel.org/doc/Documentation/usb/usbmon.txt](https://www.kernel.org/doc/Documentation/usb/usbmon.txt)
[https://elinux.org/images/1/17/USB_Debugging_and_Profiling_Techniques.pdf](https://elinux.org/images/1/17/USB_Debugging_and_Profiling_Techniques.pdf)
[https://developer.mozilla.org/en-US/docs/Web/API/USB](https://developer.mozilla.org/en-US/docs/Web/API/USB)
[https://developer.mozilla.org/en-US/docs/Web/API/USBDevice](https://developer.mozilla.org/en-US/docs/Web/API/USBDevice)
[https://github.com/ultibohub/Core/blob/master/source/rtl/ultibo/drivers/pl2303.pas](https://github.com/ultibohub/Core/blob/master/source/rtl/ultibo/drivers/pl2303.pas)
[https://github.com/torvalds/linux/blob/master/drivers/usb/serial/pl2303.c](https://github.com/torvalds/linux/blob/master/drivers/usb/serial/pl2303.c)
[https://www.beyondlogic.org/usbnutshell/usb1.shtml](https://www.beyondlogic.org/usbnutshell/usb1.shtml)
|
