Added section about USB redirection via SPICE

README.md

@@ -752,6 +752,63 @@ Successfully uninstalled nexus-server
   - [Features/CPUHotplug](https://wiki.qemu.org/Features/CPUHotplug)
   - [qmp-shell](https://github.com/0xef53/qmp-shell)
 
+## USB redirection
+
+### Introduction
+
+The spice protocol implements USB redirection which allows USB devices plugged in the PC running the spice client (remote-viewer) to be accessible in the guest OS of the VM running on the server (the server runs QEMU with an embedded Spice server).
+
+First, the `qemu-xhci` device must be added to the VM with:
+```
+-device qemu-xhci
+```
+
+Then, for each USB device to be supported and connected (on a different USB port), its vendor ID (`VID`), product ID (`PID`) and an arbitrary redirection name (`REDIR`) must be specified:
+```
+-chardev spicevmc,name=usbredir,id=REDIR -device usb-redir,filter='-1:-1:-1:-1:0|-1:VID:PID:-1:1',chardev=REDIR
+```
+
+As many devices can be specified as necessary, but each redirection name must be unique.
+
+In the syntax above, each USB device is represented by a filter which can match an arbitrary number of devices. The filter's syntax is as follow:
+```
+<class>,<vendor>,<product>,<version>,<allow>
+```
+
+Filters can be chained using the `|` operator. Here are a few examples:
+
+- `-1:-1:-1:-1:1` $\rightarrow$ allows all USB devices
+- `-1:-1:-1:-1:0` $\rightarrow$ forbids all USB devices
+- `-1:0x123:0x456:-1:1|-1:-1:-1:-1:0` $\rightarrow$ allows USB device 0x123:0x456 and forbids everything else
+
+Here is a real-world example that defines three USB redirections that forbid everything except these three USB devices (VID:PID):
+
+- A SanDisk Cruzer Blade USB key (0781:5567)
+- A Prolific Technology USB/serial (067b:2303)
+- An Atmel at91sam SAMBA bootloader (03eb:6124)
+
+```
+-device qemu-xhci -chardev spicevmc,name=usbredir,id=usbredir1 -device usb-redir,filter='-1:0x0781:0x5567:-1:1|-1:0x067b:0x2303:-1:1|-1:0x03eb:0x6124:-1:1|-1:-1:-1:-1:0',chardev=usbredir1 -chardev spicevmc,name=usbredir,id=usbredir2 -device usb-redir,filter='-1:0x0781:0x5567:-1:1|-1:0x067b:0x2303:-1:1|-1:0x03eb:0x6124:-1:1|-1:-1:-1:-1:0',chardev=usbredir2 -chardev spicevmc,name=usbredir,id=usbredir3 -device usb-redir,filter='-1:0x0781:0x5567:-1:1|-1:0x067b:0x2303:-1:1|-1:0x03eb:0x6124:-1:1|-1:-1:-1:-1:0',chardev=usbredir3
+```
+
+### Vendor ID and product ID of interest
+
+| Device description                   | Vendor ID | Product ID |
+|---                                   |---        |---         |
+| Atmel at91sam SAMBA bootloader       | 03eb      | 6124       |
+| Prolific Technology USB/serial       | 067b      | 2303       |
+| MyLab2 serial port                   | 0403      | 6015       |
+| Digilent Analog Discovery 2          | 0403      | 6014       |
+| NXP CMSIS-DAP                        | 1fc9      | 001d       |
+| Saleae Logic Pro 16                  | 21a9      | 1006       |
+| Peak USB CAN                         | 0c72      | 000c       |
+| Segger J-Link                        | 1366      | 0101       |
+| Xilinx KV260 and KR260 JTAG and UART | 0403      | 6011       |
+| Xilinx Nexys Video JTAG              | 0403      | 6010       |
+| Xilinx Nexys Video UART              | 0403      | 6001       |
+| USBest Technology USB key            | 1307      | 0165       |
+| SanDisk Cruzer Blade USB key         | 0781      | 5567       |
+
 ## Compiling QEMU from source
 
 1. Retrieve QEMU' source code from [https://www.qemu.org/download/](https://www.qemu.org/download/)