Introduction

Architecture

The CTC driver follows Linux’s Input subsystem. Input provides CTC interface to user space. The CTC software architecture is illustrated in the following figure.

The CTC software architecture contains the following parts:

Input driver: CTC driver.
Input core: Input subsystem core driver. It is the link and bridge between input driver layer and event handler layer, providing the interface downward to the hardware input driver layer and upward to the event processing layer.
Event handler: Interact with user space, it is used to report the events from the hardware driver layer to the user program.
Application: User space use. A simple example to show how to use CTC.

For more details, refer to How to Create Input Device Driver.

Implementation

CTC driver is implemented as following files:

Driver location	Introduction
<linux>/drivers/rtkdrivers/captouch/Kconfig	CTC driver Kconfig
<linux>/drivers/rtkdrivers/captouch/Makefile	CTC driver Makefile
<linux>/drivers/rtkdrivers/captouch/realtek-captouch.c	CTC functions.
<linux>/drivers/rtkdrivers/captouch/realtek-captouch.h	CTC related function declaration, macro definition, structure definition and the other header files quoted

Configuration

DTS Configure

CTC DTS node:

captouch: captouch@42010000 {
   compatible = "realtek,ameba-captouch";
   reg = <0x42010000 0x500>
      <0x420082F8 0x4>;//Control digital path input for ADC and CTC pad
   interrupts = <GIC_SPI 13 IRQ_TYPE_LEVEL_HIGH>;
   clocks = <&rcc RTK_CKE_CTC>, <&rcc RTK_CKE_ADC>;
   clock-names = "rtk_ctc_clk", "rtk_adc_clk";
   rtk,ctc-diffthr = <800>, <800>, <800>, <800>, <1000>, <1000>, <1000>, <1000>, <1000>;
   rtk,ctc-mbias = <0x18>, <0x17>, <16>, <0x1B>, <0x00>, <0x00>, <0x00>, <0x00>, <0x00>;
   rtk,ctc-nnoise = <400>, <400>, <400>, <400>, <1000>, <1000>, <1000>, <1000>, <1000>;
   rtk,ctc-pnoise = <400>, <400>, <400>, <400>, <1000>, <1000>, <1000>, <1000>, <1000>;
   rtk,ctc-ch-status = <1>, <1>, <1>, <1>, <1>, <1>,<1>, <1>, <1>;
   rtk,ctc-keycodes = <KEY_1>, <KEY_2>, <KEY_3>, <KEY_4>, <KEY_5>, <KEY_6>, <KEY_7>, <KEY_8>, <KEY_9>;
   nvmem-cells = <&efuse_ctc_mbias>;
   nvmem-cell-names = "ctc_mbias";
   status = "disabled";
};

CTC DTS Configurations

The DTS Configurations of CTC are listed in the table below.

Property	Description	Configurable?
compatible	The description of CTC driver. Default: “realtek,ameba- captouch “.	No
reg	The hardware address and size for CTC device. Default: <0x42010000 0x500>	No
interrupts	The GIC number of CTC device. Default: <GIC_SPI 13 IRQ_TYPE_LEVEL_HIGH>	No
clocks	The clock of CTC device. Default: <&rcc RTK_CKE_CTC>, <&rcc RTK_CKE_ADC>	No
rtk,ctc-diffthr	Cap-touch difference threshold for 9 channels. (see NOTE below)	0~4095
rtk,ctc-mbias	Cap-touch mbias current for 9 channels. (see NOTE below)	0~63
rtk,ctc-nnoise	Cap-touch negative noise threshold for 9 channels. (see NOTE below)	0~4095
rtk,ctc-pnoise	Cap-touch positive noise threshold for 9 channels. (see NOTE below)	0~4095
rtk,ctc-ch-status	Cap-touch channel enable control for 9 channels. 1: enable 0: disable	0/1
rtk,ctc-keycodes	Cap-touch key codes corresponding to 9 channels.	No
nvmem-cells	The nvmem cells for CTC.	Yes
nvmem-cell-names	The names of nvmen cells for CTC	Yes
status	Whether enable the device. disabled okay	Yes

Note

Each parameter 9 values are corresponding to touch0~touch8 in sequence.
Due to there are difference among channels and different boards, cap-touch is suggested to do calibration.
For the parameters ctc-diffthr, ctc-mbias, ctc-nnoise, ctc-pnoise in table above, the factory should calibrate them for each channel, and write them into EFUSE. If the values in EFUSE are empty, the value in dts file will be used instead.

Pinmux

The pin assignments of captouch are listed in the table below.

Port name	Pin name	pinctrl description
PA0	TOUCH0	<&captouch_pins >
PA1	TOUCH1	<&captouch_pins >
PA2	TOUCH2	<&captouch_pins >
PA3	TOUCH3	<&captouch_pins >
PA4	TOUCH4	<&captouch_pins >
PA5	TOUCH5	<&captouch_pins >
PA6	TOUCH6	<&captouch_pins >
PA7	TOUCH7	<&captouch_pins >
PA8	TOUCH8	<&captouch_pins >

Refer to pinctrl application note for more details.

Build Configuration

Select Device Drivers > Drivers for Realtek > Captouch driver in order:

APIs

APIs for User Space

sysfs interface is used to interact with user space, device node locates in /dev/input/eventX. User space can use open(), read() to get CTC event.

Items	Description
evdev_open	Open input device.
evdev_read	Get data from input device.

CTC demo for user space locates at: <test>/captouch.

APIs for Kernel Space

Items	Description
devm_input_allocate_device	Allocate managed input device.
input_allocate_device	Allocate memory for new input device.
input_free_device	Free memory occupied by input_dev structure
input_register_device	Register device with input core.
input_unregister_device	Unregister previously registered device.
input_event	Report new input event.

For more details, refer to Input Subsystem kernel API.