Synaptics RMI4 Multitouch PAD

This part comes from last year. I post it here for memory keeping.

Connection

• NOTE: nINT is an active-low open-drain pin for which the host must supply an external pull-up resistor.

  DISP2_DAT9        --->  Touch_nINT
  DISPB2_SER_CLK    --->  Touch_I2C_DAT
  DISPB2_SER_DIO    --->  Touch_I2C_CLK
  EIM_A16           --->  Touch_nRST1
  

Touch PAD register.

Part of register map, that we need concern.

Addr	Name	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
0x0014	Interrupt status					Abs0	Button	Status	Flash
0x0015	Button data								Left

Addr	Name	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3 - Bit 2	Bit 1 - Bit 0
0x0016	2D Finger State					Finger State 1	Finger State 0

Addr	Name	Bit 7 - Bit 0
0x0017	2D X position (11:4) Finger 0	X position [11:4]
0x0018	2D Y position (11:4) Finger 0	Y position [11:4]
0x001B	2D Z Finger 0	Z
0x001C	2D X position (11:4) Finger 1	X position [11:4]
0x001D	2D Y position (11:4) Finger 1	Y position [11:4]
0x0020	2D Z Finger 1	Z

Addr	Name	Bit 7 - Bit 4	Bit 3 - Bit 0
0x0019	2D Y/X position(3:0) Finger 0	Y Position [3:0]	X Position [3:0]
0x001A	2D Wy/Wx Finger 0	Wy	Wx
0x001E	2D Y/X position(3:0) Finger 1	Y Position [3:0]	X Position [3:0]
0x001F	2D Wy/Wx Finger 1	Wy	Wx

Get touch sample.

I2CReadForTimes(0x2c,0x14,buf,0x11); // read out register value from register addr 0x14.
  ts_sample->int_state = buf[0] & 0xF; // save interrupt status
  ts_sample->button_data = buf[1] & 0x01; // save button_data
  
  switch(buf[0x2] & 0xf) // 2D Finger State
  {
    case 0x0:
 ts_sample->contact_resistance = 0;
 break;
    case 0x01:
    case 0x02:  // bit0-1 is Finger 0 state
 ts_sample->contact_resistance = 1;
 ts_sample->x_position = (((buf[3]<<4))|(buf[5]&0xf));
 ts_sample->y_position = (((buf[4])<<4)|((buf[5]&0xf0)>>4));
 break;
    case 0x04:
    case 0x08: // bit2-3 is Finger 1 state
 ts_sample->contact_resistance = 1;
 ts_sample->x_position = (((buf[8]<<4))|(buf[10]&0xf));
 ts_sample->y_position = (((buf[9])<<4)|((buf[10]&0xf0)>>4)); 
 break;
    case 0x05:
    case 0x06:
    case 0x09:
    case 0x0a: // Finger 0 and Finger 1 press at same time
 ts_sample->contact_resistance = 2;
 ts_sample->x_position = (((buf[3]<<4))|(buf[5]&0xf));
 ts_sample->y_position = (((buf[4])<<4)|((buf[5]&0xf0)>>4));

 ts_sample->x2_position = (((buf[8]<<4))|(buf[10]&0xf));
 ts_sample->y2_position = (((buf[9])<<4)|((buf[10]&0xf0)>>4)); 
 break;

    default :
 printk("fail buf[0x16] = %d \n",buf[2]); // report real finger state value
 return -1;
  }  

Transfer to screen pixel relate position. We use 480x800 for example

if(ts_sample.int_state & 0x08) { // touch screen abs
    if (ts_sample.contact_resistance < 2) {
      if (ts_sample.x_position == 0 && ts_sample.y_position == 0 &&
 ts_sample.contact_resistance == 0) {
 x = last_x;
 y = last_y;
      }
      else
      {// transfer to screen relate position
 x = ts_sample.x_position * 480 / 1894; 
 y = 799 - ts_sample.y_position * 800 / 3245;
      }
      if (x != last_x) {
 input_report_abs(mxc_inputdev, ABS_X, x);
 last_x = x;
      }
      if (y != last_y) {
 input_report_abs(mxc_inputdev, ABS_Y, y);
 last_y = y;
      }
      /* report pressure */
      input_report_abs(mxc_inputdev, ABS_PRESSURE, ts_sample.contact_resistance);
      /* report the BTN_TOUCH */
      if (ts_sample.contact_resistance != last_press)
      {
 input_event(mxc_inputdev, EV_KEY,BTN_TOUCH, ts_sample.contact_resistance);
      }
    }
    input_sync(mxc_inputdev);
    last_press = ts_sample.contact_resistance;
  }
  else if(ts_sample.int_state & 0x04)  // button input
  {
    input_report_key(input_button,KEY_MENU,ts_sample.button_data);
  }