RT-Thread RTOS
An open source embedded real-time operating system
Input touch bridge

Touch bridge (<tt>RT_INPUT_TOUCHSCREEN</tt>)

**input_touch.c** bridges **struct rt_input_device** (Linux-style **EV_ABS** / multitouch slots) to **struct rt_touch_device** so GUI stacks can use the legacy touch class API (**rt_device_find**, **RT_TOUCH_CTRL_***, **rt_hw_touch_isr**) without duplicating panel drivers.

Input core and OFW drivers (e.g. ADS7846): Input device model (DM). Event helpers (**rt_input_setup_touch**, **rt_input_report_touch_***): Input subsystem.

Sources: **components/drivers/input/input_touch.c**, **components/drivers/input/touchscreen/**.

Kconfig

Option Role
**RT_INPUT_TOUCHSCREEN** Build **input_touch.c**; selects RT_USING_TOUCH
**RT_INPUT_TOUCHSCREEN_ADS7846** In-tree SPI resistive driver **ts-ads7846.c**
**SOC_DM_INPUT_TOUCHSCREEN_DIR** BSP adds more panel drivers

Requires **RT_USING_INPUT** and **RT_USING_DM**.

Architecture

Panel driver (e.g. ads7846)
|
| rt_input_set_capability(EV_ABS, …)
| rt_input_setup_touch(idev, num_slots, &touch_info)
| rt_input_device_register(idev)
v
input_touch_register (after idev on global list)
|
| rt_hw_touch_register → device "touchN"
| rt_input_add_handler → input_touch_cb
v
Driver reports: rt_input_report_touch_* / rt_input_sync
|
v
input_touch_cb: EV_ABS → struct rt_touch_data
SYN_REPORT → rt_hw_touch_isr()
|
v
GUI: rt_device_read / touch ISR callback
Object Role
**struct input_touch_properties** Stored in **idev->touch**: DT-derived min/max, invert, swap, slot count
**struct input_touch_device** Embeds **struct rt_touch_device** + **rt_input_handler** + per-slot **rt_touch_data**
**input_touch_ops** **touch_readpoint**, **touch_control** (range, enable/disable, status)

**input_touch_register** only creates the **rt_touch_device** when **rt_input_setup_touch** was called with non-NULL **struct rt_touch_info *info** ( **prop->touch_dev** allocated).

Driver API (<tt>input.h</tt>)

rt_err_t rt_input_setup_touch(struct rt_input_device *idev,
rt_uint32_t num_slots, struct rt_touch_info *info);
rt_err_t rt_input_parse_touch_position(struct rt_input_device *idev,
rt_uint32_t *out_x, rt_uint32_t *out_y);
rt_bool_t rt_input_report_touch_inactive(struct rt_input_device *idev, rt_bool_t active);
void rt_input_report_touch_position(struct rt_input_device *idev,
rt_uint32_t x, rt_uint32_t y, rt_bool_t multitouch);
rt_touch_info
Touch information.
Definition: dev_touch.h:162
API Role
**rt_input_setup_touch** Allocate **idev->touch**, parse DT, optional multitouch absinfo (**ABS_MT_SLOT**, **ABS_MT_TRACKING_ID**)

| **num_slots == 0** | Single-touch (**ABS_X/ABS_Y**); **num_slots > 0** | Multitouch slot protocol | | **rt_input_report_touch_position** | Apply invert/swap from DT, then **rt_input_report_abs** | | **rt_input_report_touch_inactive** | Emit **ABS_MT_TRACKING_ID = -1** on release | | **rt_input_parse_touch_position** | Map raw x/y through **touchscreen-inverted-*** / **touchscreen-swapped-x-y** |

Call **rt_input_setup_touch** before **rt_input_device_register**. **input_touch_register** runs inside register after the device is linked globally.

Device tree properties (<tt>input_touch_parse</tt>)

Read from the **rt_input_device**'s **rt_device** OFW node via **rt_dm_dev_prop_***:

Property Effect
**touchscreen-min-x**, **touchscreen-size-x**, **touchscreen-fuzz-x** Override **ABS_X** or **ABS_MT_POSITION_X** absinfo
**touchscreen-min-y**, **touchscreen-size-y**, **touchscreen-fuzz-y** Y axis
**touchscreen-max-pressure**, **touchscreen-fuzz-pressure** Pressure axis
**touchscreen-inverted-x**, **touchscreen-inverted-y** Flip coordinates in **rt_input_parse_touch_position**
**touchscreen-swapped-x-y** Swap X/Y absinfo and coordinates

Missing properties fall back to values already set by **rt_input_set_absinfo** in the panel driver.

Handler translation (<tt>input_touch_cb</tt>)

When **touch_dev->enabled**:

Input event Touch side
**ABS_MT_SLOT** Select active slot index
**ABS_MT_TRACKING_ID == -1** **RT_TOUCH_EVENT_UP**, **rt_hw_touch_isr**
**ABS_MT_TRACKING_ID valid** DOWN / MOVE, increment **down** count
**ABS_MT_POSITION_X/Y** or **ABS_X/Y** Scale raw value to **range_x/range_y** using absinfo min/max
**EV_SYN + SYN_REPORT** **rt_hw_touch_isr** (frame complete)

**input_touch_readpoint** returns one **struct rt_touch_data** for the current slot (GUI pull model).

Example (driver probe sketch)

struct rt_touch_info info = {
.type = RT_TOUCH_TYPE_CAPACITANCE,
.vendor = RT_TOUCH_VENDOR_UNKNOWN,
.point_num = 1,
.range_x = 800,
.range_y = 480,
};
rt_input_set_capability(idev, EV_ABS, ABS_X);
rt_input_set_capability(idev, EV_ABS, ABS_Y);
rt_input_set_absinfo(idev, ABS_X, 0, max_x, 0, 0);
rt_input_set_absinfo(idev, ABS_Y, 0, max_y, 0, 0);
rt_input_setup_touch(idev, 0, &info); /* 0 slots = single touch */
rt_input_device_register(idev);
/* in IRQ / thread: */
rt_input_report_touch_position(idev, x, y, RT_FALSE);
rt_input_sync(idev);

For multitouch, pass **num_slots > 0**, use **rt_input_report_touch_slot**, tracking id helpers, then **rt_input_sync** per frame.

Pitfalls

Issue Mitigation
**setup_touch after register** **input_touch_register** won't run correctly — setup before register
**info == NULL** Properties-only mode: no **rt_touch_device** exported (handler-only path not used for HW touch register)
Missing rt_input_sync Touch ISR won't see a full frame
ABS range zero Scaling in **input_touch_cb** divides by **maximum - minimum** — set absinfo first
Unregister order **input_touch_unregister** from **rt_input_device_unregister** — drop touch fd users first

See also