TOUCHSCREEN
Overview
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Functions of the Touchscreen driver
The Touchscreen driver is used to power on its integrated circuit (IC), configure and initialize hardware pins, register interrupts, configure Inter-Integrated Circuit (I2C) or SPI APIs, set input-related configurations, and download and update firmware.
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Layers of the Touchscreen driver
This section describes how to develop the touchscreen driver based on the input driver model. Figure 1 shows an overall architecture of the touchscreen driver.
The input driver is developed based on the hardware driver foundation (HDF), platform APIs, and operating system abstraction layer (OSAL) APIs. It provides hardware driver capabilities through the input Hardware Driver Interfaces (HDIs) for upper-layer input services to control the touchscreen.
Figure 1 Architecture of the input driver model
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Input driver model
The input driver model mainly consists of the device manager, common drivers, and chip drivers. The platform data channel provides capabilities for sending data generated by the touchscreen from the kernel to the user space. The driver model adapts to different touchscreen devices and hardware platforms via the configuration file, improving the efficiency of the touchscreen development. The description for each part of the input driver model is as follows:
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Input device manager: provides input device drivers with the APIs for registering or unregistering input devices and manages the input device list.
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Input common driver: provides common abstract drivers (such as the touchscreen common driver) of various input devices for initializing the board-level hardware, processing hardware interrupts, and registering input devices with the input device manager.
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Input chip driver: provides different chip drivers of each vendor. You can minimize the workload for the input chip driver development by calling differentiated APIs reserved by the input platform driver.
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Event hub: provides a unified data reporting channel, which enables input devices to report input events.
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HDF input config: parses and manages the board-level configuration as well as the private configuration of input devices.
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Advantages of developing drivers based on the HDF
The touchscreen driver is developed based on the HDF and is implemented via calls to the OSAL and platform APIs, including bus APIs and OS native APIs (such as memory, lock, thread, and timer). The OSAL and platform APIs hide the differences of underlying hardware, so that the touchscreen driver can be migrated across platforms and OSs. In this regard, you can develop the touchscreen driver only once but deploy it on multiple devices.
Available APIs
Based on the attributes of the pins, interfaces on the touchscreens can be classified into the following types:
- Power interfaces
- I/O control interfaces
- Communications interfaces
Figure 2 Common pins of the touchscreen
The interfaces shown in the figure are described as follows:
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Power interfaces
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LDO_1P8: 1.8 V digital circuits
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LDO_3P3: 3.3 V analog circuits
Generally, the touchscreen driver IC is separated from the LCD driver IC. In this case, the touchscreen driver IC requires both 1.8 V and 3.3 V power supplies. Nowadays, the touchscreen driver IC and LCD driver IC can be integrated. Therefore, the touchscreen, requires only the 1.8 V power supply, and the 3.3 V power required internally is supplied by the LCD VSP power (typical value: 5.5 V) in the driver IC.
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I/O control interfaces
- RESET: reset pin, which is used to reset the driver IC on the host when suspending or resuming the system.
- INT: interrupt pin, which needs to be set to the input direction and pull-up status during driver initialization. After detecting an external touch signal, the driver triggers the interrupt by operating the interrupt pin. The driver reads the touch reporting data in the ISR function.
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Communications interfaces
- I2C: Since only a small amount of touch data is reported by the touchscreen, I2C is used to transmit the reported data. For details about the I2C protocol and interfaces, see I2C.
- SPI: In addition to touch reporting data coordinates, some vendors need to obtain basic capacitance data. Therefore, Serial Peripheral Interface (SPI) is used to transmit such huge amount of data. For details about the SPI protocol and interfaces, see SPI.
Development Guidelines
Regardless of the OS and system on a chip (SoC), the input driver is developed based on the HDF, platform, and OSAL APIs to provide a unified driver model for touchscreen devices.
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The following uses the touchscreen driver as an example to describe the loading process of the input driver model:
(1) Complete the device description configuration, such as the loading priority, board-level hardware information, and private data, by referring to the existing template.
(2) Load the input device management driver. The input management driver is loaded automatically by the HDF to create and initialize the device manager.
(3) Load the platform driver. The platform driver is loaded automatically by the HDF to parse the board-level configuration, initialize the hardware, and provide the API for registering the touchscreen.
(4) Load the touchscreen driver. The touchscreen driver is loaded automatically by the HDF to instantiate the touchscreen device, parse the private data, and implement differentiated APIs provided by the platform.
(5) Register the instantiated touchscreen device with the platform driver. Then bind this device to the platform driver, and complete touchscreen initialization such as interrupt registration and power-on and power-off.
(6) Instantiate the input device and register it with the input manager after the touchscreen is initialized.
How to Develop
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Add the touchscreen driver-related descriptions.
Currently, the input driver is developed based on the HDF and is loaded and started by the HDF. Register the driver information, such as whether to load the driver and the loading priority in the configuration file. Then, the HDF starts the registered driver modules one by one. For details about the driver configuration, see Driver Development.
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Complete the board-level configuration and private data configuration of the touchscreen.
Configure the required I/O pins. For example, configure a register for the I2C pin reserved for the touchscreen to use I2C for transmitting data.
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Implement differentiated adaptation APIs of the touchscreen.
Use the platform APIs to perform operations for the reset pins, interrupt pins, and power based on the communications interfaces designed for boards. For details about the GPIO-related operations, see GPIO.
Development Example
This example describes how to develop the touchscreen driver.
Add the touchscreen driver-related descriptions.
The information about modules of the input driver model is shown as follows and enables the HDF to load the modules in sequence. For details, see Driver Development.
input :: host {
hostName = "input_host";
priority = 100;
device_input_manager :: device {
device0 :: deviceNode {
policy = 2; // Publish services externally.
priority = 100; // Loading priority. The input device manager in the input driver has the highest priority.
preload = 0; // Value 0 indicates that the driver is to be loaded, and value 1 indicates the opposite.
permission = 0660;
moduleName = "HDF_INPUT_MANAGER";
serviceName = "input_dev_manager";
deviceMatchAttr = "";
}
}
device_hdf_touch :: device {
device0 :: deviceNode {
policy = 2;
priority = 120;
preload = 0;
permission = 0660;
moduleName = "HDF_TOUCH";
serviceName = "event1";
deviceMatchAttr = "touch_device1";
}
}
device_touch_chip :: device {
device0 :: deviceNode {
policy = 0;
priority = 130;
preload = 0;
permission = 0660;
moduleName = "HDF_TOUCH_SAMPLE";
serviceName = "hdf_touch_sample_service";
deviceMatchAttr = "zsj_sample_5p5";
}
}
}
Board-level Hardware Configuration and Private Data Configuration
The following describes the configuration of the board-level hardware and private data of the touchscreen. You can modify the configuration based on service requirements.
root {
input_config {
touchConfig {
touch0 {
boardConfig {
match_attr = "touch_device1";
inputAttr {
inputType = 0; // Value 0 indicates that the input device is a touchscreen.
solutionX = 480;
solutionY = 960;
devName = "main_touch"; // Device name
}
busConfig {
busType = 0; // Value 0 indicates the I2C bus.
busNum = 6;
clkGpio = 86;
dataGpio = 87;
i2cClkIomux = [0x114f0048, 0x403]; // Register configuration of the i2c_clk pin
i2cDataIomux = [0x114f004c, 0x403]; // Register configuration of the i2c_data pin
}
pinConfig {
rstGpio = 3;
intGpio = 4;
rstRegCfg = [0x112f0094, 0x400]; // Register configuration of the reset pin
intRegCfg = [0x112f0098, 0x400]; // Register configuration of the interrupt pin
}
powerConfig {
vccType = 2; // Values 1, 2, and 3 indicate the low-dropout regulator (LDO), GPIO, and PMIC, respectively.
vccNum = 20; // The GPIO number is 20.
vccValue = 1800; // The voltage amplitude is 1800 mV.
vciType = 1;
vciNum = 12;
vciValue = 3300;
}
featureConfig {
capacitanceTest = 0;
gestureMode = 0;
gloverMOde = 0;
coverMode = 0;
chargerMode = 0;
knuckleMode = 0;
}
}
chipConfig {
template touchChip {
match_attr = "";
chipName = "sample";
vendorName = "zsj";
chipInfo = "AAAA11222"; // The first four characters indicate the product name. The fifth and sixth characters indicate the IC model. The last three characters indicate the chip model.
busType = 0;
deviceAddr = 0x5D;
irqFlag = 2; // Values 1 and 2 indicate that the interrupt is triggered on the rising and falling edges, respectively. Values 4 and 8 indicate that the interrupt is triggered by the high and low levels, respectively.
maxSpeed = 400;
chipVersion = 0;
powerSequence {
/* Power-on sequence is described as follows:
[Type, status, direction, delay]
<type> Value 0 indicates the power or pin is empty. Values 1 and 2 indicate the VCC (1.8 V) and VCI (3.3 V) power, respectively. Values 3 and 4 indicate the reset and interrupt pins, respectively.
<status> Values 0 and 1 indicate the power-off or pull-down, and the power-on or pull-up, respectively. Value 2 indicates that no operation is performed.
<dir> Values 0 and 1 indicate the input and output directions, respectively. Value 2 indicates that no operation is performed.
<delay> Delay time, in milliseconds.
*/
powerOnSeq = [4, 0, 1, 0,
3, 0, 1, 10,
3, 1, 2, 60,
4, 2, 0, 0];
suspendSeq = [3, 0, 2, 10];
resumeSeq = [3, 1, 2, 10];
powerOffSeq = [3, 0, 2, 10,
1, 0, 2, 20];
}
}
chip0 :: touchChip {
match_attr = "zsj_sample_5p5";
chipInfo = "ZIDN45100";
chipVersion = 0;
}
}
}
}
}
}
Adding the Touchscreen Driver
The following example shows how to implement the differentiated APIs provided by the platform driver to obtain and parse the touchscreen data. You can adjust the development process based on the board and touchscreen in use.
/* Parse the touch reporting data read from the touchscreen into coordinates. */
static void ParsePointData(ChipDevice *device, FrameData *frame, uint8_t *buf, uint8_t pointNum)
{
int32_t resX = device->driver->boardCfg->attr.resolutionX;
int32_t resY = device->driver->boardCfg->attr.resolutionY;
for (int32_t i = 0; i < pointNum; i++) {
frame->fingers[i].y = (buf[GT_POINT_SIZE * i + GT_X_LOW] & ONE_BYTE_MASK) |
((buf[GT_POINT_SIZE * i + GT_X_HIGH] & ONE_BYTE_MASK) << ONE_BYTE_OFFSET);
frame->fingers[i].x = (buf[GT_POINT_SIZE * i + GT_Y_LOW] & ONE_BYTE_MASK) |
((buf[GT_POINT_SIZE * i + GT_Y_HIGH] & ONE_BYTE_MASK) << ONE_BYTE_OFFSET);
frame->fingers[i].valid = true;
}
}
/* Obtain the touch reporting data from the chip. */
static int32_t ChipDataHandle(ChipDevice *device)
{
int32_t ret;
uint8_t touchStatus = 0;
uint8_t pointNum;
uint8_t buf[GT_POINT_SIZE * MAX_SUPPORT_POINT] = {0};
InputI2cClient *i2cClient = &device->driver->i2cClient;
uint8_t reg[GT_ADDR_LEN] = {0};
FrameData *frame = &device->driver->frameData;
reg[0] = (GT_BUF_STATE_ADDR >> ONE_BYTE_OFFSET) & ONE_BYTE_MASK;
reg[1] = GT_BUF_STATE_ADDR & ONE_BYTE_MASK;
ret = InputI2cRead(i2cClient, reg, GT_ADDR_LEN, &touchStatus, 1);
if (ret < 0 || touchStatus == GT_EVENT_INVALID) {
return HDF_FAILURE;
}
OsalMutexLock(&device->driver->mutex);
(void)memset_s(frame, sizeof(FrameData), 0, sizeof(FrameData));
if (touchStatus == GT_EVENT_UP) {
frame->realPointNum = 0;
frame->definedEvent = TOUCH_UP;
goto exit;
}
reg[0] = (GT_X_LOW_BYTE_BASE >> ONE_BYTE_OFFSET) & ONE_BYTE_MASK;
reg[1] = GT_X_LOW_BYTE_BASE & ONE_BYTE_MASK;
pointNum = touchStatus & GT_FINGER_NUM_MASK;
if (pointNum <= 0 || pointNum > MAX_SUPPORT_POINT) {
HDF_LOGE("%s: pointNum is invalid, %d", __func__, pointNum);
(void)ChipCleanBuffer(i2cClient);
OsalMutexUnlock(&device->driver->mutex);
return HDF_FAILURE;
}
frame->realPointNum = pointNum;
frame->definedEvent = TOUCH_DOWN;
/* Read the touch reporting data from the register. */
(void)InputI2cRead(i2cClient, reg, GT_ADDR_LEN, buf, GT_POINT_SIZE * pointNum);
/* Parse the touch reporting data. */
ParsePointData(device, frame, buf, pointNum);
exit:
OsalMutexUnlock(&device->driver->mutex);
if (ChipCleanBuffer(i2cClient) != HDF_SUCCESS) {
return HDF_FAILURE;
}
return HDF_SUCCESS;
}
static struct TouchChipOps g_sampleChipOps = {
.Init = ChipInit,
.Detect = ChipDetect,
.Resume = ChipResume,
.Suspend = ChipSuspend,
.DataHandle = ChipDataHandle,
};
static TouchChipCfg *ChipConfigInstance(struct HdfDeviceObject *device)
{
TouchChipCfg *chipCfg = (TouchChipCfg *)OsalMemAlloc(sizeof(TouchChipCfg));
if (chipCfg == NULL) {
HDF_LOGE("%s: instance chip config failed", __func__);
return NULL;
}
(void)memset_s(chipCfg, sizeof(TouchChipCfg), 0, sizeof(TouchChipCfg));
/* Parse the private configuration of the touchscreen. */
if (ParseTouchChipConfig(device->property, chipCfg) != HDF_SUCCESS) {
HDF_LOGE("%s: parse chip config failed", __func__);
OsalMemFree(chipCfg);
chipCfg = NULL;
}
return chipCfg;
}
static ChipDevice *ChipDeviceInstance(void)
{
ChipDevice *chipDev = (ChipDevice *)OsalMemAlloc(sizeof(ChipDevice));
if (chipDev == NULL) {
HDF_LOGE("%s: instance chip device failed", __func__);
return NULL;
}
(void)memset_s(chipDev, sizeof(ChipDevice), 0, sizeof(ChipDevice));
return chipDev;
}
static void FreeChipConfig(TouchChipCfg *config)
{
if (config->pwrSeq.pwrOn.buf != NULL) {
OsalMemFree(config->pwrSeq.pwrOn.buf);
}
if (config->pwrSeq.pwrOff.buf != NULL) {
OsalMemFree(config->pwrSeq.pwrOff.buf);
}
OsalMemFree(config);
}
static int32_t HdfSampleChipInit(struct HdfDeviceObject *device)
{
TouchChipCfg *chipCfg = NULL;
ChipDevice *chipDev = NULL;
HDF_LOGE("%s: enter", __func__);
if (device == NULL) {
return HDF_ERR_INVALID_PARAM;
}
/* Parse the private configuration of the touchscreen. */
chipCfg = ChipConfigInstance(device);
if (chipCfg == NULL) {
return HDF_ERR_MALLOC_FAIL;
}
/* Instantiate the touchscreen device. */
chipDev = ChipDeviceInstance();
if (chipDev == NULL) {
goto freeCfg;
}
chipDev->chipCfg = chipCfg;
chipDev->ops = &g_sampleChipOps;
chipDev->chipName = chipCfg->chipName;
chipDev->vendorName = chipCfg->vendorName;
/* Register the touchscreen device with the platform driver. */
if (RegisterChipDevice(chipDev) != HDF_SUCCESS) {
goto freeDev;
}
HDF_LOGI("%s: exit succ, chipName = %s", __func__, chipCfg->chipName);
return HDF_SUCCESS;
freeDev:
OsalMemFree(chipDev);
freeCfg:
FreeChipConfig(chipCfg);
return HDF_FAILURE;
}
struct HdfDriverEntry g_touchSampleChipEntry = {
.moduleVersion = 1,
.moduleName = "HDF_TOUCH_SAMPLE",
.Init = HdfSampleChipInit,
};
HDF_INIT(g_touchSampleChipEntry);