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I'm developing a project where, using a ESP32 with the esp-idf framework. I need to control, among other things, an LCD display with an SSD1963 controller, and I can only spare 8 GPIO pins for its parallel bus.

With that established, using an 8-bit bus the controller will take RGB888 data (page 17 of the datasheet).

The problem is: the LVGL library, which I'm pretty set on using, is currently unable to provide a pixel buffer in RGB888, which makes sense as 24-bit data isn't ideal for memory alignment on a 32-bit system. It can provide the buffer in ARGB8888 or RGB565, though.

The most immediate solution would be to "translate" the buffer to the desired encoding, but that would take a lot of CPU cycles and memory, both of which I'm not sure I have to spare. If I'm doing that there is no point in using esp_lcd. (maybe I'm wrong and this IS a reasonable solution?)

Is it possible for me to reconfigure the esp_lcd module's DMA to either skip the Alpha byte of ARGB8888 or "decode" RGB565? Maybe there is a better solution I'm not thinking of?

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  • \$\begingroup\$ It wouldn't be too complicated to do the conversion to RGB565 in hardware with a couple fast enough logic chips. Not sure how fast would be fast enough in this case, though, as I'm unfamiliar with this sort of application. \$\endgroup\$
    – Hearth
    Commented Nov 20, 2022 at 17:41
  • \$\begingroup\$ I have considered that, but it would complicate the bus timing control signals. It's still an option but I'd rather look for a software solution for now. \$\endgroup\$
    – rubemnobre
    Commented Nov 20, 2022 at 17:48
  • \$\begingroup\$ It seems possible to use this part in a mode similar to SPI - would that be an option? \$\endgroup\$
    – Lundin
    Commented Nov 22, 2022 at 13:33
  • \$\begingroup\$ "24 bit data isn't ideal for memory alignment on a 32 bit system" Well, no... but it can be saved in a way with zero padding, if you write a getter/setter function to obtain it. Use whatever format that's suitable for the controller/display, not whatever is suitable for some lib or MCU. \$\endgroup\$
    – Lundin
    Commented Nov 22, 2022 at 13:36
  • \$\begingroup\$ @Lundin, SPI would be ideal, but the SSD1963 controller only takes a parallel bus. The data transactions are being done with a peripheral that uses Direct Memory Access to DIRECTLY read the buffer and control the bus. "Translating" the buffer like you mentioned would be against the point of using such a peripheral, waste memory (which is on a premium) and reduce performance. My question was more related to how I could change the settings on this peripheral's DMA configuration to either decode 16 bit color or ignore one of the bytes in a 32 bit color such as ARGB8888, like you mentioned. \$\endgroup\$
    – rubemnobre
    Commented Nov 22, 2022 at 15:52

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