USB Library

Universal Serial Bus (USB) provides a serial bus standard for connecting a wide variety of devices, including computers, cell phones, game consoles, PDA’s, etc.

USB Library contains HID routines that support HID class devices, and also the generic routines that can be used with vendor specified drivers.

USB HID Class

The HID class consists primarily of devices that are used by humans to control the operation of computer systems. Typical examples of HID class devices include :

Many typical HID class devices include indicators, specialized displays, audio feedback, and force or tactile feedback. Therefore, the HID class definition includes support for various types of output directed to the end user.

Descriptor File

Each project based on the USB library should include a descriptor source file which contains vendor id and name, product id and name, report length, and other relevant information. To create a descriptor file, use the integrated USB HID terminal of mikroC PRO for ARM(Tools › USB HID Terminal). The default name for descriptor file is USBdsc.c, but you may rename it.

Library Routines

HID_Enable

Prototype

void HID_Enable(char *readbuff, char *writebuff);

Description

Enables USB HID communication.

Parameters
  • readbuff: Read Buffer.
  • writebuff: Write Buffer.

These parameters are used for HID communication.

Returns

Nothing.

Requires

Nothing.

Example
HID_Enable(&readbuff,&writebuff);
Notes

This function needs to be called before using other routines of USB HID Library.

HID_Read

Prototype

char HID_Read(void);

Description

Receives message from host and stores it in the Read Buffer.

Parameters

None.

Returns

If the data reading has failed, the function returns 0. Otherwise, it returns number of characters received from the host.

Requires

USB HID needs to be enabled before using this function. See HID_Enable.

Example
// retry until success
while(!HID_Read())
  ;
Notes

None.

HID_Write

Prototype

char HID_Write(char *writebuff, char len);

Description

Function sends data from Write Buffer writebuff to host.

Parameters
  • writebuff: Write Buffer, same parameter as used in initialization; see HID_Enable.
  • len: specifies a length of the data to be transmitted.
Returns

If the data transmitting has failed, the function returns 0. Otherwise, it returns number of transmitted bytes.

Requires

USB HID needs to be enabled before using this function. See HID_Enable.

Example
// retry until success
while(!HID_Write(&writebuff,64))
  ;
Notes

Function call needs to be repeated as long as data is not successfuly sent.

This is a blocking routine which can block the program flow. Calling USB_Break routine from the interrupt will unblock the program execution.

HID_Disable

Prototype

void HID_Disable(void);

Description

Disables USB HID communication.

Parameters

None.

Returns

Nothing.

Requires

USB HID needs to be enabled before using this function. See HID_Enable.

Example
HID_Disable();
Notes

None.

USB_Interrupt_Proc

Prototype

void USB_Interrupt_Proc(void);

Description

This routine is used for servicing various USB bus events. Should be called inside USB interrupt routine.

Parameters

None.

Returns

Nothing.

Requires

Nothing.

Example
void USB1Interrupt() iv IVT_ADDR_USB1INTERRUPT {
  USB_Interrupt_Proc();
}
Notes

Do not use this function with USB_Polling_Proc, only one should be used. To enable servicing through interrupt, USB_INTERRUPT constant should be set (it is set by default in descriptor file).

USB_Polling_Proc

Prototype

void USB_Polling_Proc(void);

Description

This routine is used for servicing various USB bus events. It should be periodically, preferably every 100 microseconds.

Parameters

None.

Returns

Nothing.

Requires

Nothing.

Example
while(1) {
  USB_Polling_Proc();
  kk = HID_Read();
  if (kk != 0) {
    for(cnt=0; cnt < 64; cnt++)
      writebuff[cnt]=readbuff[cnt];
  HID_Write(&writebuff,64);
  }
}
Notes

Do not use this functions with USB_Interrupt_Proc. To enable servicing by polling, USB_INTERRUPT constant should be set to 0 (it is located in descriptor file).

Gen_Enable

Prototype

void Gen_Enable(char* readbuff, char* writebuff);

Description

Initialize the USB module of the MCU.

Parameters
  • readbuff: Read Buffer.
  • writebuff: Write Buffer.
Returns

Nothing.

Requires

USB needs to be enabled before using this function. See HID_Enable.

Example
Gen_Enable(&readbuff,&writebuff);
Notes

None.

Gen_Read

Prototype

char Gen_Read(char *readbuff, char length, char ep);

Description

Generic routine that receives the specified data from the specified endpoint.

Parameters
  • readbuff: Received data.
  • length: The length of the data that you wish to receive.
  • ep: Endpoint number you want to receive the data into.
Returns

Returns the number of received bytes, otherwise 0.

Requires

USB needs to be enabled before using this function. See HID_Enable.

Example
while(Gen_Read(readbuff,64,1)==0)
  ;
Notes

None.

Gen_Write

Prototype

char Gen_Write(char* writebuff, char length, char ep);

Description

Sends the specified data to the specified endpoint.

Parameters
  • writebuff: The data that you want to send.
  • length: the length of the data that you wish to send.
  • ep: Endpoint number you want to send the data into.
Returns

Returns the number of transmitted bytes, otherwise 0.

Requires

USB needs to be enabled before using this function. See HID_Enable.

Example
while(Gen_Write(writebuff,64,1)==0)
  ;
Notes

This is a blocking routine which can block the program flow. Calling USB_Break routine from the interrupt will unblock the program execution.

USB_Break

Prototype

void USB_Break();

Description

HID_Write and Gen_Write are blocking routines and they can block the program flow. Calling USB_Break() routine from the interrupt will unblock the program execution. Calling this routine from interrupt will unblock the program execution. This mechanism is similar to WDT.

Parameters

None.

Returns

Nothing.

Requires Nothing.
Example

          
Notes

None.

Library Example

This example establishes connection with the HID terminal that is active on the PC. Upon connection establishment, the HID Device Name will appear in the respective window. After that software will wait for data and it will return received data back. Examples uses USBdsc.c descriptor file, which is in the same folder, and can be created by the HID Terminal.

Copy Code To ClipboardCopy Code To Clipboard
char cnt;
char kk;
char readbuff[64];
char writebuff[64];

unsigned long int i = 0;
void main(void){
  HID_Enable(&readbuff,&writebuff);

  while(1){
    USB_Polling_Proc();               // Call this routine periodically
    kk = HID_Read();
    if(kk != 0){
      for(cnt=0;cnt<64;cnt++)
        writebuff[cnt]=readbuff[cnt];
      HID_Write(&writebuff,64);
    }
  }
}
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