# Parallel IO simulation of SPI or I80 Interfaced LCD

[中文]

Parallel IO is not a bus-type peripheral. The driver directly creates a Parallel IO device for the LCD. Currently the driver supports SPI (1 bit data width) and I80 (8 bit data width) modes.

1. Create Parallel IO device by `esp_lcd_new_panel_io_parl()`. You need to set up the following parameters for a Parallel IO device:

   > - `esp_lcd_panel_io_parl_config_t::clk_src` sets the clock source of the Parallel IO device. Note, the default clock source may be different between ESP targets.

   > - `esp_lcd_panel_io_parl_config_t::clk_gpio_num` sets the GPIO number of the pixel clock (also referred as `WR` or `SCLK` in some LCD spec)

   > - `esp_lcd_panel_io_parl_config_t::dc_gpio_num` sets the GPIO number of the data or command select pin (also referred as `RS` in some LCD spec)

   > - `esp_lcd_panel_io_parl_config_t::cs_gpio_num` sets the GPIO number of the chip select pin. (Note that the Parallel IO LCD driver only supports a single LCD device).

   > - `esp_lcd_panel_io_parl_config_t::data_width` sets the bit width of the data bus (only support `1` or `8`)

   > - `esp_lcd_panel_io_parl_config_t::data_gpio_nums` is the array of the GPIO number of the data bus. The number of GPIOs should be equal to the `esp_lcd_panel_io_parl_config_t::data_width` value.

   > - `esp_lcd_panel_io_parl_config_t::max_transfer_bytes` sets the maximum number of bytes that can be transferred in one transaction.

   > - `esp_lcd_panel_io_parl_config_t::dma_burst_size` sets the number of bytes transferred by dma burst.

   > - `esp_lcd_panel_io_parl_config_t::pclk_hz` sets the pixel clock frequency in Hz. Higher pixel clock frequency results in higher refresh rate, but may cause display abnormalities if the DMA bandwidth is not sufficient or the LCD controller chip does not support high pixel clock frequency.

   > - `esp_lcd_panel_io_parl_config_t::dc_levels` sets the effective level for DC data selection and command selection.

   > - `esp_lcd_panel_io_parl_config_t::lcd_cmd_bits` and `esp_lcd_panel_io_parl_config_t::lcd_param_bits` set the bit width of the command and parameter that recognized by the LCD controller chip. This is chip specific, you should refer to your LCD spec in advance.

   > - `esp_lcd_panel_io_parl_config_t::trans_queue_depth` sets the maximum number of transactions that can be queued in the Parallel IO device. A bigger value means more transactions can be queued up, but it also consumes more memory.

   >     esp_lcd_panel_io_handle_t io_handle = NULL;
   >     esp_lcd_panel_io_parl_config_t io_config = {
   >         .clk_src = PARLIO_CLK_SRC_DEFAULT,
   >         .dc_gpio_num = EXAMPLE_PIN_NUM_DC,
   >         .clk_gpio_num = EXAMPLE_PIN_NUM_PCLK,
   >         .data_gpio_nums = {
   >             EXAMPLE_PIN_NUM_DATA0, // set DATA0 to drive SPI interfaced LCD or set DATA0~7 to drive I80 interfaced LCD
   >         },
   >         .data_width = 1, // set 1 to drive SPI interfaced LCD or set 8 to drive I80 interfaced LCD
   >         .max_transfer_bytes = EXAMPLE_LCD_H_RES * 100 * sizeof(uint16_t), // transfer 100 lines of pixels (assume pixel is RGB565) at most in one transaction
   >         .dma_burst_size = EXAMPLE_DMA_BURST_SIZE,
   >         .cs_gpio_num = EXAMPLE_PIN_NUM_CS,
   >         .pclk_hz = EXAMPLE_LCD_PIXEL_CLOCK_HZ,
   >         .trans_queue_depth = 10,
   >         .dc_levels = {
   >             .dc_cmd_level = 0,
   >             .dc_data_level = 1,
   >         },
   >         .lcd_cmd_bits = EXAMPLE_LCD_CMD_BITS,
   >         .lcd_param_bits = EXAMPLE_LCD_PARAM_BITS,
   >     };

   >     ESP_ERROR_CHECK(esp_lcd_new_panel_io_parl(&io_config, io_handle));

2. Install the LCD controller driver. The LCD controller driver is responsible for sending the commands and parameters to the LCD controller chip. In this step, you need to specify the Parallel IO device handle that allocated in the last step, and some panel specific configurations:

   > - `esp_lcd_panel_dev_config_t::reset_gpio_num` sets the LCD's hardware reset GPIO number. If the LCD does not have a hardware reset pin, set this to `-1`.

   > - `esp_lcd_panel_dev_config_t::rgb_ele_order` sets the RGB element order of each color data.

   > - `esp_lcd_panel_dev_config_t::bits_per_pixel` sets the bit width of the pixel color data. The LCD driver uses this value to calculate the number of bytes to send to the LCD controller chip.

   > - `esp_lcd_panel_dev_config_t::data_endian` specifies the data endian to be transmitted to the screen. No need to specify for color data within one byte, like RGB232. For drivers that do not support specifying data endian, this field would be ignored.

   >     esp_lcd_panel_handle_t panel_handle = NULL;
   >     esp_lcd_panel_dev_config_t panel_config = {
   >         .reset_gpio_num = EXAMPLE_PIN_NUM_RST,
   >         .rgb_ele_order = LCD_RGB_ELEMENT_ORDER_BGR,
   >         .bits_per_pixel = 16,
   >     };
   >     // Create LCD panel handle for ST7789, with the Parallel IO device handle
   >     ESP_ERROR_CHECK(esp_lcd_new_panel_st7789(io_handle, &panel_config, &panel_handle));

## API Reference

### Header File

- components/esp_lcd/include/esp_lcd_io_parl.h

- This header file can be included with:

  >     #include "esp_lcd_io_parl.h"

- This header file is a part of the API provided by the `esp_lcd` component. To declare that your component depends on `esp_lcd`, add the following to your CMakeLists.txt:

  >     REQUIRES esp_lcd

  > or

  >     PRIV_REQUIRES esp_lcd

### Functions

esp_err_t esp_lcd_new_panel_io_parl(const esp_lcd_panel_io_parl_config_t *io_config, esp_lcd_panel_io_handle_t *ret_io)

  Create LCD panel IO, for parlio interface.

  Parameters:

    - io_config -- [in] IO configuration, for parlio interface

    - ret_io -- [out] Returned panel IO handle

  Returns:

    - ESP_ERR_INVALID_ARG if parameter is invalid

    - ESP_ERR_NOT_SUPPORTED if some configuration can't be satisfied, e.g. pixel clock out of the range

    - ESP_ERR_NO_MEM if out of memory

    - ESP_OK on success

void *esp_lcd_parlio_alloc_draw_buffer(esp_lcd_panel_io_handle_t io, size_t size, uint32_t caps)

  Allocate a draw buffer that can be used by parlio interface LCD panel.

  Note

  This function differs from the normal 'heap_caps_*' functions in that it can also automatically handle the alignment required by DMA burst, cache line size, etc.

  Parameters:

    - io -- [in] Panel IO handle, created by `esp_lcd_new_panel_io_parl()`

    - size -- [in] Size of memory to be allocated

    - caps -- [in] Bitwise OR of MALLOC_CAP_* flags indicating the type of memory desired for the allocation

  Returns:

    Pointer to a new buffer of size 'size' with capabilities 'caps', or NULL if allocation failed

### Structures

struct esp_lcd_panel_io_parl_config_t

  Parallel Panel IO configuration structure, for intel 8080 interface(8 data-lines) or SPI interface(1 data-lines)

  Public Members

  gpio_num_t dc_gpio_num

    GPIO used for D/C line

  gpio_num_t clk_gpio_num

    GPIO used for CLK line

  gpio_num_t cs_gpio_num

    GPIO used for CS line

  gpio_num_t data_gpio_nums[ESP_PARLIO_LCD_WIDTH_MAX]

    GPIOs used for data lines

  size_t data_width

    Number of data lines, 1(SPI) or 8(I80)

  uint32_t pclk_hz

    Frequency of pixel clock

  parlio_clock_source_t clk_src

    Clock source for the Parlio peripheral

  size_t max_transfer_bytes

    Maximum transfer size, this determines the length of internal DMA link

  size_t dma_burst_size

    DMA burst size, in bytes

  size_t trans_queue_depth

    Transaction queue size, larger queue, higher throughput

  int lcd_cmd_bits

    Bit-width of LCD command

  int lcd_param_bits

    Bit-width of LCD parameter

  unsigned int dc_cmd_level

    Level of DC line in CMD phase

  unsigned int dc_data_level

    Level of DC line in DATA phase

  struct esp_lcd_panel_io_parl_config_t dc_levels

    Each LCD device might have its own D/C control logic

  unsigned int cs_active_high

    If set, a high level of CS line will select the device, otherwise, CS line is low level active

  struct esp_lcd_panel_io_parl_config_t flags

    Panel IO config flags

### Macros

ESP_PARLIO_LCD_WIDTH_MAX

  Maximum data width of parlio lcd interface

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