=============================
ST7796 LCD Controller driver
=============================

Overview
-------------

The `ST7796S <https://www.buydisplay.com/download/ic/ST7796S.pdf>`__ is a single-chip controller/driver for 262K-color, graphic type TFT-LCD. It consists of 960
source lines and 480 gate lines driving circuits. The ST7796S is capable of connecting directly to an external
microprocessor, and accepts 8-bit/9-bit/16-bit/18-bit parallel interface, SPI, and the ST7796S also provides
MIPI interface. Display data can be stored in the on-chip display data RAM of 320x480x18 bits. It can perform
display data RAM read-/write-operation with no external clock to minimize power consumption. In addition,
because of the integrated power supply circuit necessary to drive liquid crystal; it is possible to make a display
system with fewest components.

The ST7796 LCD controller `driver <https://github.com/lvgl/lvgl/src/drivers/display/st7796>`__ is a platform-agnostic driver, based on the `generic MIPI driver <https://github.com/lvgl/lvgl/doc/integration/drivers/display/gen_mipi.rst>`__.
It implements display initialization, supports display rotation and implements the display flush callback. The user needs to implement only two platform-specific functions to send
a command or pixel data to the controller via SPI or parallel bus. Typically these are implemented by calling the appropriate SDK library functions on the given platform.

Prerequisites
-------------

There are no prerequisites.

Configuring the driver
----------------------

Enable the ST7796 driver support in lv_conf.h, by cmake compiler define or by KConfig

.. code:: c

	#define LV_USE_ST7796  1

Usage
-----

You need to implement two platform-dependent functions:

.. code:: c

	/* Send short command to the LCD. This function shall wait until the transaction finishes. */
	int32_t my_lcd_send_cmd(lv_display_t *disp, const uint8_t *cmd, size_t cmd_size, const uint8_t *param, size_t param_size)
	{
		...
	}

	/* Send large array of pixel data to the LCD. If necessary, this function has to do the byte-swapping. This function can do the transfer in the background. */
	int32_t my_lcd_send_color(lv_display_t *disp, const uint8_t *cmd, size_t cmd_size, uint8_t *param, size_t param_size)
	{
		...
	}

To create an ST7796-based display use the function

.. code:: c

	/**
	 * Create an LCD display with ST7796 driver
	 * @param hor_res       horizontal resolution
	 * @param ver_res       vertical resolution
	 * @param flags         default configuration settings (mirror, RGB ordering, etc.)
	 * @param send_cmd      platform-dependent function to send a command to the LCD controller (usually uses polling transfer)
	 * @param send_color    platform-dependent function to send pixel data to the LCD controller (usually uses DMA transfer: must implement a 'ready' callback)
	 * @return              pointer to the created display
	 */
	lv_display_t * lv_st7796_create(uint32_t hor_res, uint32_t ver_res, lv_lcd_flag_t flags,
									lv_st7796_send_cmd_cb_t send_cmd_cb, lv_st7796_send_color_cb_t send_color_cb);


For additional details and a working example see the `generic MIPI driver documentation <https://github.com/lvgl/lvgl/doc/integration/drivers/display/gen_mipi.rst>`__.

.. note::

	You can find a step-by-step guide and the actual implementation of the callbacks on an STM32F746 using STM32CubeIDE and the ST HAL libraries here: :ref:`lcd_stm32_guide`
	
