USB Host Shield plus 2 identical joysticks

Question

I'm trying to get two identical joystics (Saitek cyborg 3D) running with the USB-Host-Shield on a Mega 2560 and an USB-Hub.

I already get the event-messages of both of them:

#include <usbhid.h>
#include <hiduniversal.h>
#include <usbhub.h>
// Satisfy IDE, which only needs to see the include statment in the ino.
#ifdef dobogusinclude
#include <spi4teensy3.h>
#endif
#include <SPI.h>
#include "hidjoystickrptparser.h"
USB Usb;
USBHub Hub(&Usb);
HIDUniversal Hid1(&Usb); // first Joystick
HIDUniversal Hid2(&Usb); // second Joystick
JoystickEvents Joy1Events;
JoystickEvents Joy2Events;
JoystickReportParser Joy1(&Joy1Events);
JoystickReportParser Joy2(&Joy2Events);
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 (!Hid1.SetReportParser(0, &Joy1))
 ErrorMessage<uint8_t > (PSTR("SetReportParser1"), 1);
 if (!Hid2.SetReportParser(0, &Joy2))
 ErrorMessage<uint8_t > (PSTR("SetReportParser2"), 1);
}
void loop() {
 Usb.Task();
 Serial.print("\tX1: ");
 PrintHex<uint8_t > (JoystickEvents::mostRecentEvent.X, 0x80);
 Serial.print("\tY1: ");
 PrintHex<uint8_t > (JoystickEvents::mostRecentEvent.Y, 0x80);
 Serial.print("\tX2: ");
 PrintHex<uint8_t > (JoystickEvents::mostRecentEvent.Z1, 0x80);
 Serial.print("\tY2: ");
 PrintHex<uint8_t > (JoystickEvents::mostRecentEvent.Z2, 0x80);
 Serial.print("\tRz: ");
 PrintHex<uint8_t > (JoystickEvents::mostRecentEvent.Rz, 0x80);
 Serial.println("");
}

My question is: How can I distinguish the events from the different joysticks.

I'm trying to get some kind of port-information from the USB-Hub. Unfortunately something like

!hid->GetAddress()

within the JoystickReportParser doesn't do the job as it always returns 0.

Any ideas?

• jsotola: look at the hub demo
• Palmstroem: That's what I'm doing since several days but I don't get the clue. I get message-events but how do I recognize from which port they do come? In the hub demo there is this function: PrintAllAddresses() which takes a pointer to the device. But it's called within this statement: Usb.ForEachUsbDevice(&PrintAllAddresses)
• Palmstroem: In the hub demo there is this function: PrintAllAddresses() which takes a pointer to the device. But it's called within this statement: Usb.ForEachUsbDevice(&PrintAllAddresses); So how would I call something like this from within the JoytickReportParser or the eventhandler OnGamepadChanged ?
• Palmstroem: Or how do I get a pointer to the device from which a message-event comes in?
• Palmstroem: To be honest. I'm not so familiar with all this pointer arithmetic. All these -> :: ! * . Is still a little bit wired to me.

Answer 1

Not quite the question that was asked but part of the problem.

This is a simple introduction to pointers.

int variable = 42; // Create a variable
int* pointer = &variable; // Create a pointer to the variable (by getting its address)
*pointer = 99; // Set the address to a new value
printf ("variable has the value %d", variable); // Print 99.

&x get the address of x

*y dereferences the pointer y, which means it 'turns it back to a variable' (this is simplistic view which isn't really true, but will do for now). So you could, if you wanted (which you wouldn't) do this *&z which would be the same as doing z.

Basically think of & and * as a pair of complimentary operators like - and + or * and /. (They aren't operators, but to start with it might help).

The next problem is when you do this

SomeFunction(&variable);

All function parameters in C/C++ are passed by value by default. This means the function gets a copy of them not the actual value. So if you had:

void FunctionOne (int val)
{
 val = 99;
}
int val = 4;
FunctionOne(val);
printf("val = %d", val); // You will see 4 printed.

If you pass by reference then you will see 99 printed, to pass by reference you can do it one of two ways.

void FunctionTwo (int& valByRef);
void FunctionThree (int* valPointer);

FunctionTwo only works with C++ (It will work with an Arduino).

FunctionThree might cause a segmentation error if NULL is passed in and the function writes to it.

If it helps in my opinion pointers was one of the hardest concepts to grasp in classic C/C++ so don't worry if you don't understand it just have a play with it and see what you can do.

Calling Methods

• object.method() - Call the function method on the instance called object which is of type X.
• object->method() - Call the function method on the instance called object which is a pointer of type X.
• object::method() - call the function method which is a static member of class object (static means it doesn't change any data within an instance of a class)
• *object->method() - Avoid this like the plague. It either means *(object->method()) or (*object)->method() to know you would need to look at the type of object and the return type of the function. Its easier just to bracket it to remove ambiguity.

As for *object.&method() I've never come across that one, but that doesn't mean it doesn't exist. :)

• user31481: Those who don't understand pointers are doomed to program in Javascript the rest of their lives.
• Palmstroem: Thank you very much for this explanation. Good explanation! What confuses me is: Sometimes you can access a property by object.method or by object.object.method then by object::method and object->method or object.&method or *object.&object::method and object.@->/!%&wtf$method and so on. These things were not made for human brains to be understood.
• Code Gorilla: Are you saying I'm not human? :) (See edit) Its learning a new language, and you just have to remember certain rules, the more you use them the more they become ingrained, there is no short cut :(
• Palmstroem: Thank you very much. Superhuman! Any ideas for the original question? I'm inside a signal-handler-function and want to access an attribute of a parent or grand-parent class, but don't know how to find the right method. The documentation at felis.github.io/USB_Host_Shield_2.0/… seems to be quite comprehensive. But I don't get the clue.
• Palmstroem: !Hid->GetAddress() always returns 0. Maybe I need to do something like *evt.HIDDevice.Hid->GetAddress() but all trials like that lead to compile errors.

Answer 2

this could be a possible answer, in Arduino Code, the USB Host Shield 2.0 library is necessary:

#include <usbhid.h> 
#include <hiduniversal.h> 
#include <usbhub.h> 
// Logitech Attack 3 HID report 
struct GamePadEventData { 
 uint8_t X, Y, Z1, Z2, Rz; 
} __attribute__((packed)); 
class JoystickEvents { 
 public: virtual void OnGamePadChanged(const GamePadEventData *evt, int joystick); 
}; 
class JoystickReportParser : public HIDReportParser { 
 JoystickEvents *joyEvents; 
 uint8_t joyId; 
 uint8_t oldPad[sizeof(GamePadEventData)]; 
 public: JoystickReportParser(JoystickEvents *evt, uint8_t id) : joyEvents(evt), joyId(id) {} 
 virtual void Parse(USBHID *hid, bool is_rpt_id, uint8_t len, uint8_t *buf); 
}; 
void JoystickReportParser::Parse(USBHID *hid, bool is_rpt_id, uint8_t len, uint8_t *buf) { 
 if (!is_rpt_id && len == sizeof(GamePadEventData)) { 
 // Checking if there are changes in report since the method was last called
 bool match = (sizeof(oldPad) == len) && (memcmp(oldPad, buf, len) == 0); 
 if (!match && joyEvents) { 
 joyEvents->OnGamePadChanged((const GamePadEventData*)buf, joyId); 
 memcpy(oldPad, buf, len); 
 }
 } 
} 
 
void JoystickEvents::OnGamePadChanged(const GamePadEventData *evt, int joystick) { 
 Serial.print("Joystick "); 
 Serial.print(joystick); 
 Serial.print(": X: "); PrintHex<uint16_t>(evt->X, 0x80); 
 Serial.print(" Y: "); PrintHex<uint16_t>(evt->Y, 0x80); 
 Serial.print(" Z1: "); PrintHex<uint8_t>(evt->Z1, 0x80); 
 Serial.print(" Z2: "); PrintHex<uint8_t>(evt->Z2, 0x80); 
 Serial.print(" Rz: "); PrintHex<uint8_t>(evt->Rz, 0x80); 
 Serial.println(); 
} 
USB Usb; 
USBHub Hub(&Usb); 
HIDUniversal Hid1(&Usb); // first Joystick 
HIDUniversal Hid2(&Usb); // second Joystick 
JoystickEvents JoyEvents; 
JoystickReportParser Joy1(&JoyEvents, 1); 
JoystickReportParser Joy2(&JoyEvents, 2); 
void setup() { 
 Serial.begin(115200); 
 
 Serial.println("Start"); 
 
 if (Usb.Init() == -1) { 
 Serial.println("OSC did not start."); 
 } 
 
 delay(200); 
 
 if (!Hid1.SetReportParser(0, &Joy1) || !Hid2.SetReportParser(1, &Joy2)) { 
 ErrorMessage<uint8_t>(PSTR("SetReportParser"), 1); 
 } 
} 
void loop() {
 Usb.Task(); 
}