LG31MU97 MacOS 50Hz patched EDID

DisplayProductID-76e7

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>DisplayPixelDimensions</key>
        <data>
        AAAQAAAACHA=
        </data>
        <key>DisplayProductID</key>
        <integer>30439</integer>
        <key>DisplayProductName</key>
        <string>31MU97</string>
        <key>DisplayVendorID</key>
        <integer>7789</integer>
        <key>IODisplayEDID</key>
        <data>
        AP///////wAebed2AQEBAQEYAQSlRiV4mB3xrk81syUNUFQhCABxQIGAgcCpwNHAAQEB
        AQEBUNAAoPBwPoAIkGUMjW8hAAAaKGgAoPBwPoAIkGUMjW8hAAAaAAAAEAAAAAAAAAAA
        AAAAAAAAAAAA/AAzMU1VOTcKICAgICAgAv0CAxHwRBAEAwEjCQcHgwEAAAI6gBhxOC1A
        WCxFALhvIQAAHgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
        AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
        x3AReQMAAwAUtLgAh/8PnwA7AFcAbwg9AC8ABwAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
        AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
        AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAECQ
        </data>
        <key>SwitchResX backuped settings</key>
        <dict>
                <key>DisplayProductID</key>
                <integer>30439</integer>
                <key>DisplayVendorID</key>
                <integer>7789</integer>
                <key>IODisplayEDID</key>
                <data>
                AP///////wAebed2AQEBAQEYAQSlRiV4mB3xrk81syUNUFQhCABxQIGAgcCp
                wNHAAQEBAQEBUNAAoPBwPoAIkGUMjW8hAAAaKGgAoPBwPoAIkGUMjW8hAAAa
                AAAAEAAAAAAAAAAAAAAAAAAAAAAA/AAzMU1VOTcKICAgICAgAv0CAxHwRBAE
                AwEjCQcHgwEAAAI6gBhxOC1AWCxFALhvIQAAHgAAAAAAAAAAAAAAAAAAAAAA
                AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
                AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAx3AReQMAAwAoeNkAh/8P
                TwAHAB8Abwg9AC8ABwC0uACH/w+fADsAVwBvCD0ALwAHAAAAAAAAAAAAAAAA
                AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
                AAAAAAAAAAAAAAAAAAAAAAAAAAAAAOeQ
                </data>
        </dict>
        <key>default-resolution</key>
        <data>
        AAAQAAAACHAAMgAA
        </data>
        <key>trng</key>
        <data>
        gGhGAEBgAABoAHIAAAAAAPcfMwMBAAAAeAAAAAAAAAB/BUgAAAAAAABGwyMAAAAAQJJI
        AEBgAABAyZPs/n8AAAoAAAAyAAAAECcAACChBwAwxTQDAQAAAAEAAAAAAAAA+MmT7P5/
        AAD3HzMDAQAAAIBoRgBAYAAAAMMfAEBgAAA3ADQANgA4AAAAAAAAAAAAAAAAAAAAAAAA
        AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
        AAAAAAAAAAAAAAAAcB2TV/HGXkIAAAAAAAAAAAAAAAAAAAAA
        </data>
</dict>
</plist>

fix-edid.go

package main

import (
	"bufio"
	"errors"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"os"
)

func check(e error) {
	if e != nil {
		panic(e)
	}
}

const recordLength = 128

func main() {

	var inputPath, outputPath string
	flag.StringVar(&inputPath, "in", "", "input file, default STDIN")
	flag.StringVar(&outputPath, "out", "", "output file, default STDOUT")
	flag.Parse()

	// read from STDIN if no input file was provided
	input := os.Stdin
	if inputPath != "" {
		f, err := os.Open(inputPath)
		check(err)
		input = f
	}
	reader := bufio.NewReader(input)

	// write to STDOUT if no output file was provided
	output := os.Stdout
	if outputPath != "" {
		f, err := os.Create(outputPath)
		check(err)
		output = f
	}
	writer := bufio.NewWriter(output)
	defer writer.Flush()

	orginal, err := ioutil.ReadAll(reader)
	check(err)

	// ensure that we have a least three records
	sz := len(orginal)
	fmt.Printf("Byte length: %d\n", sz)
	if sz < 3*recordLength {
		log.Fatalf("Data smaller (%d) than expected (%d).\n", sz, 3*recordLength)
	}
	data := []byte{}

	// create an index for easy access
	//
	// we want to skip two records as we know the last
	// record is the one we are interested in
	thirdRecordIndex := 2 * recordLength
	x := thirdRecordIndex

	for i := range orginal {
		switch {

		// everything between 0 - 5 is meta data that we don't
		// really need to touch. Its start getting intersting with index 7
		//
		// each Timing Descriptor Block is 20 bytes long
		// record[7] indicates how many Timing Descriptor Blocks
		// 20 => 1 block, 40 => 2 blocks, 60 => 3 blocks etc.
		//
		// as we want to reduce that no. of blocks from 2 to 1 we
		// need to set this one to 20, so it indicates only 1 block exists
		case i == x+7:
			data = append(data, 20)

		// map 2nd record to place of 1st
		// 1st record = record[8] - record[27]
		// 2nd record = record[28] - record[47]
		case i >= x+8 && i <= x+27:
			data = append(data, orginal[i+20])

		// zero the 2nd Timing Descriptor Block
		// as that one was moved to the first one
		case i >= x+28 && i <= x+47:
			data = append(data, 0x00)

		// add newly calculated checksum
		case i == x+126:
			// data = append(data, 0x40)
			checksum, err := calculateChecksumForRecord(x, data)
			if err != nil {
				log.Fatalln(err)
			}
			data = append(data, checksum)

		default:
			data = append(data, orginal[i])
		}
	}

	writer.Write(data)
	// ioutil.WriteFile(fixedFilepath, data, 0644)
}

func calculateChecksumForRecord(recordIndex int, data []byte) (byte, error) {
	if len(data)-recordIndex < 126 {
		return byte(0), errors.New("Can't calculate checksum for record smaller than 127 bytes")
	}

	// exclude the DisplayID magic byte from checksum
	var sum byte
	for i := recordIndex + 1; i < len(data); i++ {
		sum = sum + data[i]
	}

	checksum := -sum & 0xff
	fmt.Println("Cheksum: ", checksum)
	return byte(checksum), nil
}