List the display timings on an M1 Mac

M1MacTimings.sh

#!/bin/bash

# by joevt Jan 7/2021


dodump=1
if [[ "$1" == "-s" ]]; then
	dodump=0
	shift
fi


plisttojson () {
	local theparam=""
	if [[ "$1" == "-r" ]]; then
		theparam="$1"
		shift
	fi

	local sedscript='
		/^'$'\t''*<data>/,/^'$'\t''*<\/data>/ {
			/^('$'\t''*)<data>(.*)/ { s//\1<string>_data:\2/; h; d; };
			/^'$'\t''*<\/data>(.*)/! { s/^'$'\t''+(.*)/\1/; H; d; };
			/^'$'\t''*<\/data>(.*)/ { s//:data_<\/string>\1/; H; g; s/\n//g; };
		}
	'
	{
		if [[ -n "$1" ]]; then
			sed -E "$sedscript" "$1"
		else
			sed -E "$sedscript"
		fi || { echo "# sed failed" 1>&2 ; return 1 ; }
	} | { plutil -convert json $theparam - -o - || { echo "# plutil failed" 1>&2 ; return 1 ; } ; }

	return 0
}


dumpM1MacTimings () {
	local theplist="$1"

	if [[ -z "$theplist" ]]; then
		theplist="$(mktemp)"
		ioreg -alr -k "display-timing-info" > "$theplist"
	fi

	local st_size=0
	eval "$(stat -s "$theplist")"
	if ((st_size == 0)); then
		echo "# Error: display-timing-info not found" 1>&2
		exit 1
	fi

	plisttojson "$theplist" | { perl -e '
		use JSON::PP;

		my $ioreg = decode_json (<>);

		my $parentname;

		sub donode {
			my $node = $_[0];
	
			if ($node->{"IOObjectClass"} eq "AppleCLCD2") {
				print "\n$parentname:\n";
				for my $timingelement (@{$node->{"TimingElements"}}) {
					printf(
						"%s%dx%d%s@%.3fHz %.3fkHz %.2fMHz  h(%d %d %d %s)  v(%d %d %d %s)  %s%s%s%s%s\n",
						((exists $node->{"DPTimingModeId"}) && $timingelement->{"ID"} eq $node->{"DPTimingModeId"}) ? " -> " : "    ",
						$timingelement->{"HorizontalAttributes"}{"Active"},
						$timingelement->{"VerticalAttributes"}{"Active"},
						$timingelement->{"IsInterlaced"} ? "i" : "",

						$timingelement->{"VerticalAttributes"}{"PreciseSyncRate"} / 65536.0,
						$timingelement->{"HorizontalAttributes"}{"PreciseSyncRate"} / 65536.0,
						$timingelement->{"HorizontalAttributes"}{"PreciseSyncRate"} * $timingelement->{"HorizontalAttributes"}{"Total"} / 65536000.0,

						$timingelement->{"HorizontalAttributes"}{"FrontPorch"},
						$timingelement->{"HorizontalAttributes"}{"SyncWidth"},
						$timingelement->{"HorizontalAttributes"}{"BackPorch"},
						$timingelement->{"HorizontalAttributes"}{"SyncPolarity"} ? "+" : "-",

						$timingelement->{"VerticalAttributes"}{"FrontPorch"},
						$timingelement->{"VerticalAttributes"}{"SyncWidth"},
						$timingelement->{"VerticalAttributes"}{"BackPorch"},
						$timingelement->{"VerticalAttributes"}{"SyncPolarity"} ? "+" : "-",

						$timingelement->{"IsOverscanned"} ? " (overscan)" : "",
						$timingelement->{"IsPreferred"} ? " (preferred)" : "",
						$timingelement->{"IsPromoted"} ? " (promoted)" : "",
						$timingelement->{"IsSplit"} ? " (tiled)" : "",
						$timingelement->{"IsVirtual"} ? " (virtual)" : ""
					);
				}
			}
			else
			{
				$parentname = $node->{"IORegistryEntryName"};
				foreach my $childnode (@{$node->{"IORegistryEntryChildren"}}) {
					donode($childnode);
				}
			}
		}

		foreach my $node (@{$ioreg}) {
			donode($node);
		}
	'  \
	|| echo "# perl failed" 1>&2 ; }
}

if ((dodump)); then
	dumpM1MacTimings "$1"
fi

Download

curl -L https://gist.github.com/joevt/e862b0088ef58b9144877d01401bcee8/raw -o ~/Downloads/M1MacTimings.sh

Run

# on an M1 Mac, get the ioreg info for the displays:
ioreg -alr -k "display-timing-info" > ioreg_M1.plist

# then use the downloaded script to list the timings:
bash ~/Downloads/M1MacTimings.sh ioreg_M1.plist

# or run the script with no parameters to get the current timings:
bash ~/Downloads/M1MacTimings.sh