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adzialocha / it8951-video

Play videos on IT8951-controlled e-paper displays

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Cool project - any suggestions to get vcom value?

kimmobrunfeldt opened this issue · comments

commented

Hi! I've been playing with the usb based controlling using https://sr.ht/~martijnbraam/it8951/ C code as the basis. I wasn't able to get the current vcom value using this code. Have you successfully queried the vcom value? The USB programming pdf sheet had an example command:

unsigned char get_vcom_cmd[16] = {
  0xfe, // Customer command.
  0x00,
  0x00,
  0x00,
  0x00,
  0x00,
  0xa3,  // PMIC (Power Management Integrated Circuits) command.
  0x00,
  0x00,
  0x00,   // Do Set VCom? (0 – no, 1 – yes)
  0x00,
  0x00,
  0x00,
  0x00,
  0x00,
  0x00,
};

but it didn't describe the return shape or length in bytes.

As a reference, Waveshare has a GPIO based C code example.

commented

Hey @kimmobrunfeldt! 👋

I just made an experiment and could retreive the data with the command you've mentioned. The result you're receiving is a "word" (that is two bytes, or 16 bit).

The VCOM value of my display is -1.58, which is represented as 1580 (decimal) or 062c (hex). When I run the 0xa3 command I receive 062c 👍 - this is the code I've used:

let data = [
    CUSTOMER_CMD, // 0xfe
    0x00,
    0x00,
    0x00,
    0x00,
    0x00,
    PMIC_CONTROL_CMD, // 0xa3
    0x00,
    0x00,
    0x00,
    0x00,
    0x00,
    0x00,
    0x00,
    0x00,
    0x00,
];

// https://github.com/adzialocha/it8951-video/blob/main/src/usb.rs#L47
let result: u16 = self
    .connection
    .read_command(&data, bincode::options().with_big_endian())?;

println!("{:x}", result); // 062c
commented

@adzialocha ok awesome, thanks for testing!
Then it seems like my C code might have an issue with reading data.

commented

Finally figured it out with the help of your example code. I didn't spot the "FROM" vs "TO" difference before, now with correct communication direction it works: kimmobrunfeldt/eink-weather-display@84b60bf

commented

Super ☺️