Arduino Isochronous USB

Arduino M0 Isochronous USB IN transaction without changing the ArduinoCore

The ArduinoCore for the SAMD21 does not support Isochronous USB datatransfer. This gitHub provides the code to implement support for Isochronous USB IN transactions at the max of 1023bytes per transfer (ie. streaming data from controller TO laptop). The code implements a speed of around 1MB/S or 10Mb/s. (10,000 x (1023+51)bytes per 10s from Wireshark) The code provides a library that adds the Isochronous port to Windows keeping the ability to use Serial print accross the common port.

What you find:

1. The Arduino Sketch implementing Isochronous USB IN transactions
2. The Atmel code implementing Isochronous USB IN transactions
3. The Visual studio C++ code implementing a WinUSB based driver for receiving the Isochronous datatransfer in memory databuffer. (new version!)

The VS C++ code is renewed and provides a C DLL library with several functions as: Initialize Start Stop Read Copy The library provides the class as well as the DLL exports, exposing it to external applications.

References for reading: On USB protocol:

			http://www.usbmadesimple.co.uk/

On Arduino's PluggableUSB framework:

			https://github.com/arduino/Arduino/wiki/PluggableUSB-and-PluggableHID-howto

On WinUSB api for windows receiving end:

			https://docs.microsoft.com/en-us/windows-hardware/drivers/usbcon/windows-desktop-app-for-a-usb-device

			https://docs.microsoft.com/en-us/windows-hardware/drivers/usbcon/how-to-write-a-windows-desktop-app-that-communicates-with-a-usb-device

			https://docs.microsoft.com/en-us/windows-hardware/drivers/usbcon/getting-set-up-to-use-windows-devices-usb

Further detail around some tests I did comparing the BULK, ie. standard data transfer using Serial.print and Isochronous datatransfer.

1. Test description: -Run iterative ADC reads for 5 seconds (using RTC clock).

   Keep number of iterations made = Test result
   Write ADC read to Serial.print in:

   package of 2 bytes (serial.print)
   
   package of 52 bytes (serial.print)
   
   package of 1023 bytes (isochronous)
   
   no writing
   

   Test results:

   2 bytes: 33 000 iterations
   
   52 bytes: 30 000 iterations
   
   1023 bytes: 1 293 000 iterations
   
   no writing: 1 318 000 iterations
   

This test would therefore indicate it is certainly worthwhile to consider Isochronous datatransfers, in time critical applications.

What I did notice during my testing was that Windows will initialize an Isochronous datatransfer on an 8ms interval not faster. Doing the math, one could conclude it is not faster than a normal Bulk transfer (which transmits 52bytes on 0.2ms). However the overhead that the Bulk transfer imposes on the processor seems to completely offset this as shown by the tests above.

Using Isochronous datatransfer, on the other hand, implies transmitting 1023bytes every 8ms, eg. 1x1023bytes/8ms or 2x1023/12ms or 3x1023/14ms, ....

Hope it can inspire you,

Keep making!