max7219: add buffering

[nopnop2002]

I am requesting a driver for MAX7219.

Add one parameter to max7219_draw_image_8x8.

esp_err_t max7219_draw_image_8x8(max7219_t *dev, uint8_t pos, const void *image, bool flag)

---

If flag = true, immediately issue an SPI to the device.

        for (uint8_t c = 0; c < CASCADE_SIZE; c ++)
            max7219_draw_image_8x8(&dev, c * 8, (uint8_t *)symbols + c * 8 + offs, true);

When CASCADE_SIZE is 4, such data is output to SPI.

[0x01 0xff]
[0x01 0xff 0x00 0x00]
[0x01 0xff 0x00 0x00 0x00 0x00]
[0x01 0xff 0x00 0x00 0x00 0x00 0x00 0x00]

The bottom row of the four Matrix LEDs turns ON.

---

If flag = false, data is saved in the [INTERNAL buffer] and SPI is not issued to the device.
[INTERNAL buffer] is uint8_t buffer[CASCADE_SIZE*8] like this:

typedef struct
{
    spi_device_interface_config_t spi_cfg;
    spi_device_handle_t spi_dev;
    uint8_t digits;              //!< Accessible digits in 7seg. Up to cascade_size * 8
    uint8_t cascade_size;        //!< Up to `MAX7219_MAX_CASCADE_SIZE` MAX721xx cascaded
    bool mirrored;               //!< true for horizontally mirrored displays
    bool bcd;
    uint8_t internal_buffer[64];
} max7219_t;

When max7219_flash is executed, SPI is issued to the device based on the data in the [INTERNAL buffer].

        for (uint8_t c = 0; c < CASCADE_SIZE; c ++)
            max7219_draw_image_8x8(&dev, c * 8, (uint8_t *)symbols + c * 8 + offs, false);
        max7219_flash(&dev);

When CASCADE_SIZE is 4, such data is output to SPI.

[0x01 0xff 0x01 0xff 0x01 0xff 0x01 0xff]

The bottom row of the four Matrix LEDs turns ON.

It can be displayed at high speed.

---

I tried the same approach in the Arduino environment.
It's 23 times faster.

https://github.com/nopnop2002/Arduino-MatrixControl

Thank you.

[UncleRus]

Good idea, but implementing it will break compatibility.
I will think about it.

[nopnop2002]

How about hiding the flag variable inside the structure like this?

typedef struct
{
    spi_device_interface_config_t spi_cfg;
    spi_device_handle_t spi_dev;
    uint8_t digits;              //!< Accessible digits in 7seg. Up to cascade_size * 8
    uint8_t cascade_size;        //!< Up to `MAX7219_MAX_CASCADE_SIZE` MAX721xx cascaded
    bool mirrored;               //!< true for horizontally mirrored displays
    bool bcd;
    bool flag;                   //Whether to buffer the SPI output
    uint8_t internal_buffer[64];
} max7219_t;