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Using fbtft with 4DPi-35

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  • Using fbtft with 4DPi-35

    I was wondering if it is possible to use the fbtft (, but are now included as kernel staging drivers) with the 4DPi-35. I took a look at the source that is posted on your bitbucket account. The compatible = "4dsystems,35-hat" line from the 4dpi-35 device tree source matches with code in 4d-hats.c which makes many references to the HX8357. I know from the datasheet that a Xilinx XC9572XL is driving the display, but there is no documentation on how it is programmed. After reading your source, I made the assumption that it was using an HX8357-compatible SPI protocol. I wrote myself a new devicetree to use the fb_hx8357 module from the fbtft project, but I get no output on the display. To save myself further frustration, I was wondering if the 4DPi-35 (rev 2) is in fact compatible with the HX8357 format? Is there any documentation on how the XC9572XL is set up?

  • #2
    I have read through the source of the official drivers, and it seems that the startup command sequence is the same as that of the HX8357, except for one magic command. In the source:
    static u8 hx8357_seq_c2[] = { 0xC2, 0x00, 0x08, 0x04, };
    Can anyone official comment on what the purpose of this command is? Is it enabling the SPI compression? Can I disable the compression so that vanilla SPI works?


    • #3

      hx8357_seq_c2[] is a part of HX8357 based LCD panel initialization. It was in the recommended initialization for the panel, although the 0xc2 command is undocumented so I do not really know what is it for (or if it is indeed necessary)... The command is not related to compression.


      • #4
        The init sequence is as supplied by the manufacturer, and often, contains an undocumented command.

        Sometimes these commands appear in updated datasheets, sometimes they don't.

        In this case the comment in the init sequence is 'Set Gate EQ', make of that what you will.