USB host shield Mouse scroll wheel

[falkobabbage]

Hi all,

I have been trying to get the detection of a scroll wheel of a regular mouse working with a USB Host Shield.

I am using Host Shield Library 2.0 for this but I cannot find a way to get any info from the scroll wheel that I can use. The only useful example that I found was with the provided USBHID_desc.ino script in the examples of that library. Here the serial returns that it found a "wheel" and gives me a good value when I scroll up or down.
I could not reverse-engineer how this is done however, since I have a severe lack of knowledge on how USB (and HID) work in this context (or any context at all for that matter).

Is there a way such that I can retrieve those wheel values so that I can use them in my own script?

Kind regards,
Falko

#include <usbhid.h>
#include <hiduniversal.h>
#include <hidescriptorparser.h>
#include <usbhub.h>
#include "pgmstrings.h"

// Satisfy the IDE, which needs to see the include statment in the ino too.
#ifdef dobogusinclude
#include <spi4teensy3.h>
#endif
#include <SPI.h>

class HIDUniversal2 : public HIDUniversal
{
public:
    HIDUniversal2(USB *usb) : HIDUniversal(usb) {};

protected:
    uint8_t OnInitSuccessful();
};

uint8_t HIDUniversal2::OnInitSuccessful()
{
    uint8_t    rcode;

    HexDumper<USBReadParser, uint16_t, uint16_t>    Hex;
    ReportDescParser                                Rpt;

    if ((rcode = GetReportDescr(0, &Hex)))
        goto FailGetReportDescr1;

    if ((rcode = GetReportDescr(0, &Rpt)))
	goto FailGetReportDescr2;

    return 0;

FailGetReportDescr1:
    USBTRACE("GetReportDescr1:");
    goto Fail;

FailGetReportDescr2:
    USBTRACE("GetReportDescr2:");
    goto Fail;

Fail:
    Serial.println(rcode, HEX);
    Release();
    return rcode;
}

USB Usb;
//USBHub Hub(&Usb);
HIDUniversal2 Hid(&Usb);
UniversalReportParser Uni;

void setup()
{
  Serial.begin( 115200 );
#if !defined(__MIPSEL__)
  while (!Serial); // Wait for serial port to connect - used on Leonardo, Teensy and other boards with built-in USB CDC serial connection
#endif
  Serial.println("Start");

  if (Usb.Init() == -1)
      Serial.println("OSC did not start.");

  delay( 200 );

  if (!Hid.SetReportParser(0, &Uni))
      ErrorMessage<uint8_t>(PSTR("SetReportParser"), 1  );
}

void loop()
{
    Usb.Task();
}