Initial commit: Schunix as it stands before the SchOS rename

An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.

tools/ttyshot.ps1

@@ -0,0 +1,92 @@
+# Photograph the framebuffer console after driving it with escape sequences.
+#
+# The serial line and the framebuffer are two different consumers of console
+# output, and they behave differently on purpose: escapes are passed through
+# to the serial line verbatim (a real terminal emulator is on the other end
+# and understands them better than we do) and *interpreted* for the
+# framebuffer. So the serial transcript can never tell you whether the escape
+# parser works -- it contains the raw bytes either way. Only a picture can.
+#
+#   tools\ttyshot.ps1
+
+param(
+    [int]$BootSeconds = 22,
+    [string]$Out = "build\ttyshot.ppm",
+    [string]$Qemu = "$env:USERPROFILE\scoop\apps\qemu\current\qemu-system-x86_64.exe"
+)
+
+$ErrorActionPreference = 'Stop'
+$root = Split-Path $PSScriptRoot -Parent
+$hda  = Join-Path $root 'schunix.img'
+$hdb  = Join-Path $root 'build\fs.img'
+$log  = Join-Path $root 'build\ttyshot.log'
+$ppm  = Join-Path $root $Out
+$monPort = 55571
+
+# Each line exercises one thing the console could not do before: colour,
+# bright colour, background colour, cursor addressing, erase-to-end-of-line,
+# and non-ASCII text.
+$commands = @(
+    'clear'
+    'printf ''\033[31mRED \033[32mGREEN \033[34mBLUE \033[35mMAGENTA \033[36mCYAN \033[0mdefault\n'''
+    'printf ''\033[1;31mbold red \033[1;32mbold green \033[1;34mbold blue\033[0m\n'''
+    'printf ''\033[37;44m white on blue \033[0m normal\n'''
+    'printf ''caf\303\251 \303\251t\303\251 na\303\257ve \303\274ber sch\303\266n a\303\261o\n'''
+    'printf ''ERASED-THIS\033[13G\033[Kkept this\n'''
+    'printf ''\033[12;40Hcursor addressed to row 12 col 40\n'''
+    # Tab used to be drawn as glyph 9, which in CP437 is a hollow circle --
+    # so pressing Tab printed a circle instead of moving the cursor. Every
+    # other control character had the same problem waiting behind it.
+    'printf ''A\tB\tC\tD -- tabs, not circles\n'''
+)
+
+$psi = New-Object System.Diagnostics.ProcessStartInfo
+$psi.FileName = $Qemu
+$psi.Arguments = @(
+    "-drive file=`"$hda`",format=raw,index=0,media=disk"
+    "-drive file=`"$hdb`",format=raw,index=1,media=disk"
+    '-m 1G -smp 1 -cpu qemu64,+rdtscp -machine pc-i440fx-9.2'
+    '-display none'
+    "-chardev stdio,id=c0,logfile=`"$log`""
+    '-serial chardev:c0'
+    "-monitor tcp:127.0.0.1:$monPort,server,nowait"
+) -join ' '
+$psi.RedirectStandardInput = $true
+$psi.UseShellExecute       = $false
+
+Write-Host '==> booting' -ForegroundColor Cyan
+$p = [System.Diagnostics.Process]::Start($psi)
+
+try {
+    Start-Sleep -Seconds $BootSeconds
+    foreach ($cmd in $commands) {
+        Write-Host "  > $cmd" -ForegroundColor DarkGray
+        foreach ($ch in ($cmd + "`n").ToCharArray()) {
+            $p.StandardInput.Write($ch)
+            $p.StandardInput.Flush()
+            Start-Sleep -Milliseconds 20   # serial has no flow control
+        }
+        Start-Sleep -Seconds 2
+    }
+
+    Write-Host '==> capturing the framebuffer' -ForegroundColor Cyan
+    $client = New-Object System.Net.Sockets.TcpClient('127.0.0.1', $monPort)
+    $writer = New-Object System.IO.StreamWriter($client.GetStream())
+    $writer.AutoFlush = $true
+    Start-Sleep -Milliseconds 500
+    $writer.WriteLine("screendump $ppm")
+    Start-Sleep -Seconds 2
+    $writer.WriteLine('quit')
+    Start-Sleep -Milliseconds 500
+    $client.Close()
+} finally {
+    if (-not $p.HasExited) { $p.Kill() }
+    Start-Sleep -Milliseconds 800
+}
+
+if (Test-Path $ppm) {
+    Write-Host "==> $ppm ($((Get-Item $ppm).Length) bytes)" -ForegroundColor Green
+} else {
+    Write-Host 'FAIL: no screendump was produced' -ForegroundColor Red
+    exit 1
+}