Clear staticcheck, gopls and go.mod warnings

fb.go

@@ -31,6 +31,9 @@ const (
 	viScreenInfoLen = 40
 )
 
+// w and h are the logical canvas, which is portrait; pw and ph are the panel,
+// which is landscape. Every draw is turned a quarter turn on its way to memory,
+// so logical top lands on the panel's right edge.
 type framebuffer struct {
 	file   *os.File
 	tty    *os.File
@@ -38,12 +41,22 @@ type framebuffer struct {
 	back   []byte
 	w      int
 	h      int
+	pw     int
+	ph     int
 	stride int
 	rShift uint
 	gShift uint
 	bShift uint
 }
 
+func (fb *framebuffer) offset(x, y int) int {
+	return x*fb.stride + (fb.pw-1-y)*4
+}
+
+func (fb *framebuffer) fromPanel(x, y int) (int, int) {
+	return y, fb.pw - 1 - x
+}
+
 // The kernel console draws into the same framebuffer, including a blinking
 // cursor and any keyboard echo, which fights every frame we write. Putting the
 // active console into graphics mode stops it touching the framebuffer at all.
@@ -88,21 +101,23 @@ func openFramebuffer(path string) (*framebuffer, error) {
 
 	fb := &framebuffer{
 		file:   f,
-		w:      int(vi[viXres]),
-		h:      int(vi[viYres]),
+		pw:     int(vi[viXres]),
+		ph:     int(vi[viYres]),
+		w:      int(vi[viYres]),
+		h:      int(vi[viXres]),
 		stride: int(stride),
 		rShift: uint(vi[viRedOffset]),
 		gShift: uint(vi[viGreenOffset]),
 		bShift: uint(vi[viBlueOffset]),
 	}
 
-	fb.mem, err = unix.Mmap(int(f.Fd()), 0, fb.stride*fb.h,
+	fb.mem, err = unix.Mmap(int(f.Fd()), 0, fb.stride*fb.ph,
 		unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED)
 	if err != nil {
 		f.Close()
 		return nil, fmt.Errorf("mmap: %w", err)
 	}
-	fb.back = make([]byte, fb.stride*fb.h)
+	fb.back = make([]byte, fb.stride*fb.ph)
 
 	fb.tty, err = takeConsole()
 	if err != nil {
@@ -139,28 +154,28 @@ func (fb *framebuffer) fill(c rgb) {
 		row[x+2] = byte(v >> 16)
 		row[x+3] = byte(v >> 24)
 	}
-	for y := 0; y < fb.h; y++ {
+	for y := 0; y < fb.ph; y++ {
 		copy(fb.back[y*fb.stride:], row)
 	}
 }
 
+// One logical column is contiguous after the turn, so it fills a span at a time.
 func (fb *framebuffer) rect(x0, y0, w, h int, c rgb) {
+	x1, y1 := min(x0+w, fb.w), min(y0+h, fb.h)
+	x0, y0 = max(x0, 0), max(y0, 0)
+	if x0 >= x1 || y0 >= y1 {
+		return
+	}
 	v := fb.pixel(c)
-	for y := y0; y < y0+h; y++ {
-		if y < 0 || y >= fb.h {
-			continue
-		}
-		base := y * fb.stride
-		for x := x0; x < x0+w; x++ {
-			if x < 0 || x >= fb.w {
-				continue
-			}
-			o := base + x*4
-			fb.back[o+0] = byte(v)
-			fb.back[o+1] = byte(v >> 8)
-			fb.back[o+2] = byte(v >> 16)
-			fb.back[o+3] = byte(v >> 24)
-		}
+	span := make([]byte, (y1-y0)*4)
+	for i := 0; i+4 <= len(span); i += 4 {
+		span[i+0] = byte(v)
+		span[i+1] = byte(v >> 8)
+		span[i+2] = byte(v >> 16)
+		span[i+3] = byte(v >> 24)
+	}
+	for x := x0; x < x1; x++ {
+		copy(fb.back[fb.offset(x, y1-1):], span)
 	}
 }
 
@@ -169,7 +184,7 @@ func (fb *framebuffer) blend(x, y int, c rgb, cov uint8) {
 	if x < 0 || y < 0 || x >= fb.w || y >= fb.h || cov == 0 {
 		return
 	}
-	o := y*fb.stride + x*4
+	o := fb.offset(x, y)
 	if cov == 255 {
 		v := fb.pixel(c)
 		fb.back[o+0] = byte(v)

frame.go

@@ -60,14 +60,6 @@ var patterns = []pattern{
 	}},
 }
 
-func patternNames() []string {
-	names := make([]string, len(patterns))
-	for i, p := range patterns {
-		names[i] = p.name
-	}
-	return names
-}
-
 // Every pattern is laid out at full length up front with its checksum at each
 // size, so a sender picks a pattern by choosing a buffer, never by writing one.
 type frameSpec struct {

go.mod

@@ -3,7 +3,8 @@ module g.fc.run/theater/cabletest
 go 1.26.5
 
 require (
-	golang.org/x/image v0.44.0 // indirect
-	golang.org/x/sys v0.47.0 // indirect
-	golang.org/x/text v0.40.0 // indirect
+	golang.org/x/image v0.44.0
+	golang.org/x/sys v0.47.0
 )
+
+require golang.org/x/text v0.40.0 // indirect

main.go

@@ -58,8 +58,14 @@ type direction struct {
 	drops       uint64
 	errBase     sample
 	dropBase    uint64
+	nicRaw      uint64
 	nicNow      uint64
 	nicBase     uint64
+
+	recent      errs
+	recentBase  sample
+	recentDrops uint64
+	recentNic   uint64
 }
 
 // Smoothing has to be steady against high-frequency noise yet still chase a
@@ -84,7 +90,13 @@ type rateEstimator struct {
 	n     int
 }
 
-func (e *rateEstimator) update(x float64) {
+// While the rate window is still growing it already averages everything there
+// is, so smoothing it again would only average in the startup ramp twice.
+func (e *rateEstimator) update(x float64, windowFull bool) {
+	if !windowFull {
+		e.est, e.shown, e.mad, e.n = x, x, 0, 0
+		return
+	}
 	if e.n == 0 {
 		e.est, e.shown, e.n = x, x, 1
 		return
@@ -147,6 +159,27 @@ type rateSample struct {
 	txFrames, txBytes, rxFrames, rxBytes uint64
 }
 
+// Late is counted but left out of the total, since a reordered frame arrived.
+type errs struct {
+	lost, late    uint64
+	crc, badMagic uint64
+	badLen        uint64
+	kdrop, link   uint64
+}
+
+func (e errs) total() uint64 {
+	return e.lost + e.crc + e.badMagic + e.badLen + e.kdrop + e.link
+}
+
+func (e errs) add(o errs) errs {
+	return errs{
+		lost: e.lost + o.lost, late: e.late + o.late,
+		crc: e.crc + o.crc, badMagic: e.badMagic + o.badMagic,
+		badLen: e.badLen + o.badLen,
+		kdrop:  e.kdrop + o.kdrop, link: e.link + o.link,
+	}
+}
+
 // A sliding window: the counters are sampled every frame and the rate is taken
 // across the whole window, so the figure moves every frame while still being
 // measured over a long enough span to be steady.
@@ -311,40 +344,51 @@ var intervalCols = []colSpec{
 // One interval's numbers, shared by the console table and the framebuffer so
 // both always show the same figures.
 type view struct {
-	txPPS, rxPPS     float64
-	txGbps, rxGbps   float64
-	txFrames, txSent uint64
-	rxFrames, rxGot  uint64
-	lost, late       uint64
-	crc, badMagic    uint64
-	kdrop, link      uint64
-	errors           uint64
-	cable            cableView
+	txPPS, rxPPS    float64
+	txGbps, rxGbps  float64
+	rxFrames, rxGot uint64
+	since           errs
+	window          errs
+	cable           cableView
 }
 
 // Cumulative fields, which need no rate window and are identical for both the
 // console and the display.
 func (d *direction) counters(now sample) view {
 	b := d.errBase
-	v := view{
-		txFrames: now.txFrames - b.txFrames,
-		txSent:   now.txBytes - b.txBytes,
+	return view{
 		rxFrames: now.rxFrames - b.rxFrames,
 		rxGot:    now.rxBytes - b.rxBytes,
-		lost:     now.lost - b.lost,
-		late:     now.late - b.late,
-		crc:      now.crcErr - b.crcErr,
-		badMagic: now.badMagic - b.badMagic,
-		kdrop:    d.drops - d.dropBase,
 		cable:    d.cable.view(),
+		since: errs{
+			lost:     now.lost - b.lost,
+			late:     now.late - b.late,
+			crc:      now.crcErr - b.crcErr,
+			badMagic: now.badMagic - b.badMagic,
+			badLen:   now.badLen - b.badLen,
+			kdrop:    d.drops - d.dropBase,
+			// A frame the stack refused and a frame the driver dropped are the same
+			// failure seen from either side of the ring, and never the same frame
+			// twice: a send that fails never reaches the driver to be dropped.
+			link: d.nicNow - d.nicBase +
+				(now.txErrs - b.txErrs) + (now.rxErrs - b.rxErrs),
+		},
 	}
-	// A frame the stack refused and a frame the driver dropped are the same
-	// failure seen from either side of the ring, and never the same frame twice:
-	// a send that fails never reaches the driver to be dropped.
-	v.link = d.nicNow - d.nicBase +
-		(now.txErrs - b.txErrs) + (now.rxErrs - b.rxErrs)
-	v.errors = v.lost + v.crc + v.badMagic + (now.badLen - b.badLen) + v.kdrop + v.link
-	return v
+}
+
+func totalView(views []view) view {
+	var t view
+	for _, v := range views {
+		t.txPPS += v.txPPS
+		t.rxPPS += v.rxPPS
+		t.txGbps += v.txGbps
+		t.rxGbps += v.rxGbps
+		t.rxFrames += v.rxFrames
+		t.rxGot += v.rxGot
+		t.since = t.since.add(v.since)
+		t.window = t.window.add(v.window)
+	}
+	return t
 }
 
 func (d *direction) view(prev *sample, secs float64) view {
@@ -369,8 +413,9 @@ func (d *direction) displayView(t time.Time) view {
 	d.win.push(rateSample{t, now.txFrames, now.txBytes, now.rxFrames, now.rxBytes})
 
 	v := d.counters(now)
-	v.txFrames = d.heldFrames.get(t, v.txFrames)
-	v.txSent = d.heldSent.get(t, v.txSent)
+	v.window = d.recent
+	v.rxFrames = d.heldFrames.get(t, v.rxFrames)
+	v.rxGot = d.heldSent.get(t, v.rxGot)
 
 	o, n, ok := d.win.span()
 	if !ok {
@@ -382,10 +427,11 @@ func (d *direction) displayView(t time.Time) view {
 	}
 	txF := n.txFrames - o.txFrames
 	rxF := n.rxFrames - o.rxFrames
-	d.est.txPPS.update(float64(txF) / secs)
-	d.est.rxPPS.update(float64(rxF) / secs)
-	d.est.txGbps.update(gbps(n.txBytes-o.txBytes, txF, secs))
-	d.est.rxGbps.update(gbps(n.rxBytes-o.rxBytes, rxF, secs))
+	full := d.win.filled
+	d.est.txPPS.update(float64(txF)/secs, full)
+	d.est.rxPPS.update(float64(rxF)/secs, full)
+	d.est.txGbps.update(gbps(n.txBytes-o.txBytes, txF, secs), full)
+	d.est.rxGbps.update(gbps(n.rxBytes-o.rxBytes, rxF, secs), full)
 
 	v.txPPS = d.est.txPPS.value()
 	v.rxPPS = d.est.rxPPS.value()
@@ -402,24 +448,64 @@ func (d *direction) row(elapsed time.Duration, v view, target float64, length st
 		rateCell(v.txGbps, target),
 		commas(uint64(v.rxPPS)),
 		rateCell(v.rxGbps, target),
-		statusCell(v.lost),
-		statusCell(v.late),
-		statusCell(v.crc),
-		statusCell(v.badMagic),
-		statusCell(v.kdrop),
-		statusCell(v.link),
-		statusCell(v.errors),
+		statusCell(v.since.lost),
+		statusCell(v.since.late),
+		statusCell(v.since.crc),
+		statusCell(v.since.badMagic),
+		statusCell(v.since.kdrop),
+		statusCell(v.since.link),
+		statusCell(v.since.total()),
 		paint(v.cable.minText(), cCyan),
 		paint(length, cCyan),
 	}
 }
 
-// Sampled once a second, since these are sysfs reads; the display uses whatever
-// the last sample left behind.
+// Sampled once a second, since these are sysfs reads. The recent errors roll
+// here rather than over the rate window because the nic counters only move at
+// this rate, and a shorter span would alias them into a flicker.
 func (d *direction) sampleNIC() {
+	d.accumulateNIC()
+
+	now := d.snapshot()
+	b := d.recentBase
+	d.recent = errs{
+		lost:     now.lost - b.lost,
+		late:     now.late - b.late,
+		crc:      now.crcErr - b.crcErr,
+		badMagic: now.badMagic - b.badMagic,
+		badLen:   now.badLen - b.badLen,
+		kdrop:    d.drops - d.recentDrops,
+		link: d.nicNow - d.recentNic +
+			(now.txErrs - b.txErrs) + (now.rxErrs - b.rxErrs),
+	}
+	d.recentBase, d.recentDrops, d.recentNic = now, d.drops, d.nicNow
+}
+
+func (d *direction) readNICTotal() uint64 {
 	tx := readNIC(d.tx.name)
 	rx := readNIC(d.rx.name)
-	d.nicNow = tx.tx + rx.rx + tx.carrierDown
+	return tx.tx + rx.rx + tx.carrierDown
+}
+
+// Sysfs nic counters run from boot and restart from zero whenever the driver
+// resets its statistics, so only their forward motion is accumulated. Taking
+// raw differences instead charges a boot's worth of errors to the first sample
+// and turns a reset into a near-2^64 underflow.
+func (d *direction) accumulateNIC() {
+	raw := d.readNICTotal()
+	if raw > d.nicRaw {
+		d.nicNow += raw - d.nicRaw
+	}
+	d.nicRaw = raw
+}
+
+// Whatever the interfaces counted before now is not ours, and no interval has
+// elapsed yet, so every baseline starts here and nothing is reported until the
+// first one completes.
+func (d *direction) primeCounters() {
+	d.nicRaw = d.readNICTotal()
+	d.reset()
+	d.recentBase, d.recentDrops, d.recentNic = d.snapshot(), d.drops, d.nicNow
 }
 
 func buildDirection(label string, tx, rx endpoint, sizes []int, cfg config) (*direction, error) {
@@ -471,9 +557,6 @@ func buildDirection(label string, tx, rx endpoint, sizes []int, cfg config) (*di
 	}
 	d.probeRxFD = fd
 
-	// Whatever the interfaces have counted before now is not ours.
-	d.sampleNIC()
-	d.nicBase = d.nicNow
 	return d, nil
 }
 
@@ -539,7 +622,6 @@ type config struct {
 	streams    int
 	batch      int
 	probeEther uint16
-	zeroNS     float64
 	nsPerM     float64
 }
 
@@ -550,13 +632,13 @@ func main() {
 		sizesArg = flag.String("sizes", "64,128,256,512,1024,1280,1514", "frame sizes in bytes, excluding FCS, cycled per packet")
 		streams  = flag.Int("streams", 7, "independent streams per direction, capped by rx rings; each gets its own ethertype, steered by a flow rule to its own rx queue")
 		batch    = flag.Int("batch", 64, "frames per sendmmsg/recvmmsg call")
-		zeroNS   = flag.Float64("zero-ns", 2163.77, "mean of both directions at zero cable length; belongs to the media adapters, recalibrate when they change")
-		nsPerM   = flag.Float64("ns-per-m", 5.4545, "mean of both directions, per metre of cable")
+
+		nsPerM = flag.Float64("ns-per-m", 5.2, "mean of both directions, per metre of cable")
 	)
 	flag.Parse()
 
 	if err := run(*aName, *bName, *sizesArg,
-		*streams, *batch, *zeroNS, *nsPerM); err != nil {
+		*streams, *batch, *nsPerM); err != nil {
 		fmt.Fprintln(os.Stderr, "error:", err)
 		os.Exit(1)
 	}
@@ -574,7 +656,7 @@ const (
 )
 
 func run(aName, bName, sizesArg string,
-	nStreams, batch int, zeroNS, nsPerM float64) error {
+	nStreams, batch int, nsPerM float64) error {
 
 	if aName == "" || bName == "" {
 		return fmt.Errorf("both -a and -b are required")
@@ -629,7 +711,6 @@ func run(aName, bName, sizesArg string,
 		streams:    nStreams,
 		batch:      batch,
 		probeEther: uint16(etherBase + nStreams),
-		zeroNS:     zeroNS,
 		nsPerM:     nsPerM,
 	}
 
@@ -674,7 +755,7 @@ func run(aName, bName, sizesArg string,
 				nStreams, ethertypes[0], ethertypes[len(ethertypes)-1])},
 			{"probe", fmt.Sprintf("ethertype 0x%04x every %s", cfg.probeEther, probeInterval)},
 			{"batch", fmt.Sprintf("%d frames per syscall", batch)},
-			{"calibration", fmt.Sprintf("%g ns at zero length, %g ns/m", zeroNS, nsPerM)},
+			{"calibration", fmt.Sprintf("%g ns/m, zero taken from the shortest delay seen so far", nsPerM)},
 			{"buffers", fmt.Sprintf("sndbuf %s, rcvbuf %s",
 				humanBytes(uint64(sockBufSize(dirs[0].txFDs[0], unix.SO_SNDBUF))),
 				humanBytes(uint64(sockBufSize(dirs[0].rxFDs[0], unix.SO_RCVBUF))))},
@@ -705,11 +786,15 @@ func run(aName, bName, sizesArg string,
 	}
 	defer disp.close()
 
-	touch, err := watchTouch(disp.fb.w, disp.fb.h)
+	touch, err := watchTouch(disp.fb.pw, disp.fb.ph)
 	if err != nil {
 		return fmt.Errorf("touchscreen: %w", err)
 	}
 
+	for _, d := range dirs {
+		d.primeCounters()
+	}
+
 	start := time.Now()
 	close(startTx)
 	tick := time.NewTicker(reportInterval)
@@ -735,13 +820,20 @@ func run(aName, bName, sizesArg string,
 		case <-space:
 			start = resetAll(dirs, stats)
 		case now := <-frame.C:
-			if x, y, down := touch.get(); disp.holdReset(x, y, down, now) {
+			px, py, down := touch.get()
+			x, y := disp.fb.fromPanel(px, py)
+			if disp.holdReset(x, y, down, now) {
 				start = resetAll(dirs, stats)
 			}
 			for i, d := range dirs {
 				views[i] = d.displayView(now)
 			}
-			disp.render(dirs, views, now.Sub(start), target, cfg.cableText(views))
+			cable := "-"
+			if m, ok := cfg.cableMetres(views); ok {
+				cable = fmt.Sprintf("%.1f m", m)
+			}
+			disp.render(totalView(views), now.Sub(start),
+				target*float64(len(dirs)), cable)
 		case now := <-tick.C:
 			secs := now.Sub(last).Seconds()
 			last = now

probe.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"fmt"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -34,18 +33,20 @@ type cableStats struct {
 	mu      sync.Mutex
 	min     int64
 	samples uint64
+	floor   int64
 
 	txPend map[uint64]int64
 	rxPend map[uint64]int64
 }
 
 type cableView struct {
-	min     int64
-	samples uint64
+	min   int64
+	floor int64
+	ok    bool
 }
 
 func (v cableView) minText() string {
-	if v.samples == 0 {
+	if !v.ok {
 		return "-"
 	}
 	return commasInt(v.min)
@@ -57,23 +58,14 @@ func (c config) cableMetres(views []view) (float64, bool) {
 	if len(views) == 0 {
 		return 0, false
 	}
-	var sum float64
+	var excess float64
 	for _, v := range views {
-		if v.cable.samples == 0 {
+		if !v.cable.ok {
 			return 0, false
 		}
-		sum += float64(v.cable.min)
+		excess += float64(v.cable.min - v.cable.floor)
 	}
-	mean := sum / float64(len(views))
-	return (mean - c.zeroNS) / c.nsPerM, true
-}
-
-func (c config) cableText(views []view) string {
-	m, ok := c.cableMetres(views)
-	if !ok {
-		return ""
-	}
-	return fmt.Sprintf("cable %.1f m", m)
+	return excess / float64(len(views)) / c.nsPerM, true
 }
 
 func newCableStats() *cableStats {
@@ -114,13 +106,16 @@ func (c *cableStats) put(seq uint64, ts int64, tx bool) {
 	if c.samples == 0 || delta < c.min {
 		c.min = delta
 	}
+	if c.floor == 0 || delta < c.floor {
+		c.floor = delta
+	}
 	c.samples++
 }
 
 func (c *cableStats) view() cableView {
 	c.mu.Lock()
 	defer c.mu.Unlock()
-	return cableView{c.min, c.samples}
+	return cableView{c.min, c.floor, c.samples > 0}
 }
 
 func (c *cableStats) reset() {

render.go

@@ -199,14 +199,18 @@ func renderBox(title string, headers []string, rights []bool, rows [][]string) s
 	}
 
 	var b strings.Builder
-	if title != "" {
-		b.WriteString(paint(title, cBold+cCyan) + "\n")
+	writeln := func(s string) {
+		b.WriteString(s)
+		b.WriteByte('\n')
 	}
-	b.WriteString(line("┌", "┬", "┐") + "\n")
-	b.WriteString(rowText(headers, true) + "\n")
-	b.WriteString(line("├", "┼", "┤") + "\n")
+	if title != "" {
+		writeln(paint(title, cBold+cCyan))
+	}
+	writeln(line("┌", "┬", "┐"))
+	writeln(rowText(headers, true))
+	writeln(line("├", "┼", "┤"))
 	for _, r := range rows {
-		b.WriteString(rowText(r, false) + "\n")
+		writeln(rowText(r, false))
 	}
 	b.WriteString(line("└", "┴", "┘"))
 	return b.String()

ui.go

@@ -8,39 +8,27 @@ import (
 
 var (
 	uiBg     = rgb{0x12, 0x14, 0x18}
-	uiPanel  = rgb{0x1c, 0x20, 0x26}
-	uiRule   = rgb{0x2e, 0x34, 0x3c}
+	uiOKFill = rgb{0x18, 0x42, 0x26}
+	uiOKEdge = rgb{0x3c, 0xe0, 0x70}
+	uiErrFil = rgb{0x54, 0x18, 0x1c}
+	uiErrEdg = rgb{0xff, 0x46, 0x46}
 	uiButton = rgb{0x25, 0x2b, 0x33}
 	uiFg     = rgb{0xe6, 0xe8, 0xea}
-	uiDim    = rgb{0x7a, 0x82, 0x8c}
+	uiDim    = rgb{0x9a, 0xa2, 0xac}
 	uiCyan   = rgb{0x5c, 0xc8, 0xe0}
-	uiGreen  = rgb{0x4c, 0xc2, 0x6a}
-	uiRed    = rgb{0xe0, 0x4b, 0x4b}
+	uiGreen  = rgb{0x6c, 0xdc, 0x86}
+	uiRed    = rgb{0xf0, 0x6b, 0x6b}
 	uiYellow = rgb{0xe0, 0xb0, 0x40}
 )
 
-// Everything tabular sits on one monospace cell grid and every number is
-// right-aligned to a column end, so columns line up by construction.
 const (
 	uiMargin = 16
+	uiPad    = 14
+	uiBorder = 12
+	rowGap   = 5
+	blockGap = 16
 
-	cellDirA  = 0
-	cellArrow = 2
-	cellDirB  = 4
-
-	colTxGbEnd  = 14
-	colTxPPSEnd = 27
-	colRxGbEnd  = 37
-	colRxPPSEnd = 50
-
-	colFramesEnd = 18
-	colDataEnd   = 27
-	colLostEnd   = 38
-	colLateEnd   = 46
-	colCRCEnd    = 53
-	colKdropEnd  = 62
-
-	btnW         = 200
+	btnW         = 240
 	btnH         = 64
 	holdDuration = time.Second
 )
@@ -58,12 +46,15 @@ type display struct {
 	huge  *textFace
 	grid  *textFace
 	gridB *textFace
-	small *textFace
 
-	resetBtn  rect
-	holdStart time.Time
-	holdFrac  float64
-	fired     bool
+	nowPanel   rect
+	sincePanel rect
+	nowH       int
+	sinceH     int
+	resetBtn   rect
+	holdStart  time.Time
+	holdFrac   float64
+	fired      bool
 }
 
 func newDisplay() (*display, error) {
@@ -77,10 +68,9 @@ func newDisplay() (*display, error) {
 		bold bool
 		size float64
 	}{
-		{&d.huge, true, 72},
-		{&d.grid, false, 24},
-		{&d.gridB, true, 24},
-		{&d.small, false, 18},
+		{&d.huge, true, 60},
+		{&d.grid, false, 22},
+		{&d.gridB, true, 22},
 	} {
 		face, err := loadFace(spec.bold, spec.size)
 		if err != nil {
@@ -94,9 +84,22 @@ func newDisplay() (*display, error) {
 		return nil, fmt.Errorf("grid faces disagree on cell width: %d vs %d",
 			d.grid.cellW, d.gridB.cellW)
 	}
+	// Guessed heights collide on a screen this small, so the split follows what
+	// the loaded faces actually measure.
+	gridLine := d.grid.cellH + rowGap
+	errH := len(errRows) * gridLine
+	d.nowH = d.huge.cellH + rowGap + gridLine + blockGap + errH
+	d.sinceH = 4*gridLine + blockGap + errH + blockGap + btnH
+
+	inner := fb.w - 2*uiMargin
+	chrome := 2 * (uiBorder + uiPad)
+	avail := fb.h - 2*uiMargin - blockGap
+	h1 := (avail-2*chrome)*d.nowH/(d.nowH+d.sinceH) + chrome
+	d.nowPanel = rect{uiMargin, uiMargin, inner, h1}
+	d.sincePanel = rect{uiMargin, uiMargin + h1 + blockGap, inner, avail - h1}
 	d.resetBtn = rect{
-		x: fb.w - uiMargin - btnW,
-		y: fb.h - uiMargin - btnH,
+		x: d.sincePanel.x + (inner-btnW)/2,
+		y: d.sincePanel.y + d.sincePanel.h - uiBorder - uiPad - btnH,
 		w: btnW,
 		h: btnH,
 	}
@@ -163,28 +166,59 @@ func (d *display) close() {
 	d.fb.close()
 }
 
-func (d *display) cellX(c int) int {
-	return uiMargin + c*d.grid.cellW
-}
-
-func (d *display) at(c, y int, s string, col rgb) {
-	d.grid.draw(d.fb, d.cellX(c), y, s, col)
-}
-
-func (d *display) atBold(c, y int, s string, col rgb) {
-	d.gridB.draw(d.fb, d.cellX(c), y, s, col)
-}
-
-func (d *display) rightAt(cEnd, y int, s string, col rgb) {
-	d.grid.draw(d.fb, d.cellX(cEnd)-len([]rune(s))*d.grid.cellW, y, s, col)
-}
-
 func (d *display) right(f *textFace, xEnd, y int, s string, col rgb) {
 	f.draw(d.fb, xEnd-len([]rune(s))*f.cellW, y, s, col)
 }
 
-func (d *display) center(f *textFace, y int, s string, col rgb) {
-	f.draw(d.fb, (d.fb.w-len([]rune(s))*f.cellW)/2, y, s, col)
+func (d *display) row(f *textFace, x, w, y int, label, value string, col rgb) int {
+	f.draw(d.fb, x, y, label, uiDim)
+	d.right(f, x+w, y, value, col)
+	return y + f.cellH + rowGap
+}
+
+func (d *display) rateRow(x, w, y int, label string, gb, target float64) int {
+	d.gridB.draw(d.fb, x, y+(d.huge.cellH-d.gridB.cellH)/2, label, uiDim)
+	d.right(d.huge, x+w, y, fmt.Sprintf("%.2f Gb/s", gb), rateColor(gb, target))
+	return y + d.huge.cellH + rowGap
+}
+
+var errRows = []struct {
+	label string
+	get   func(errs) uint64
+}{
+	{"lost", func(e errs) uint64 { return e.lost }},
+	{"late", func(e errs) uint64 { return e.late }},
+	{"crc", func(e errs) uint64 { return e.crc }},
+	{"bad magic", func(e errs) uint64 { return e.badMagic }},
+	{"bad length", func(e errs) uint64 { return e.badLen }},
+	{"kernel drops", func(e errs) uint64 { return e.kdrop }},
+	{"link", func(e errs) uint64 { return e.link }},
+}
+
+func (d *display) errBlock(x, w, y int, e errs) int {
+	for _, r := range errRows {
+		n := r.get(e)
+		y = d.row(d.grid, x, w, y, r.label, commas(n), errColor(n))
+	}
+	return y
+}
+
+func (d *display) panel(p rect, e errs, contentH int) (int, int, int) {
+	fill, edge := uiOKFill, uiOKEdge
+	if e.total() > 0 {
+		fill, edge = uiErrFil, uiErrEdg
+	}
+	d.fb.rect(p.x, p.y, p.w, p.h, edge)
+	d.fb.rect(p.x+uiBorder, p.y+uiBorder,
+		p.w-2*uiBorder, p.h-2*uiBorder, fill)
+
+	inset := uiBorder + uiPad
+	x, w := p.x+inset, p.w-2*inset
+	y := p.y + inset
+	if slack := (p.y + p.h - inset) - y - contentH; slack > 0 {
+		y += slack / 2
+	}
+	return x, w, y
 }
 
 // Rendered rates are quantised so the text only changes when the value moves
@@ -216,101 +250,22 @@ func rateColor(gb, target float64) rgb {
 	}
 }
 
-func (d *display) render(dirs []*direction, views []view, elapsed time.Duration, target float64, cable string) {
+func (d *display) render(v view, elapsed time.Duration, target float64, cable string) {
 	fb := d.fb
 	fb.fill(uiBg)
 
-	d.small.draw(fb, uiMargin, 10, "cabletest", uiCyan)
-	d.small.draw(fb, uiMargin+11*d.small.cellW, 10,
-		fmt.Sprintf("%s %s   %s %s", dirs[0].tx.tag, dirs[0].tx.name,
-			dirs[0].rx.tag, dirs[0].rx.name), uiDim)
-	d.right(d.small, fb.w-uiMargin, 10, uptime(elapsed), uiDim)
+	x, w, y := d.panel(d.nowPanel, v.window, d.nowH)
+	y = d.rateRow(x, w, y, "RX", v.rxGbps, target)
+	y = d.row(d.grid, x, w, y, "packets/s", commas(roundPPS(v.rxPPS)), uiFg)
+	d.errBlock(x, w, y+blockGap, v.window)
 
-	var total uint64
-	for _, v := range views {
-		total += v.errors
-	}
-
-	bandY, bandH := 40, 150
-	fb.rect(0, bandY, fb.w, bandH, uiPanel)
-	fb.rect(0, bandY, 8, bandH, errColor(total))
-	word, wc := "NO ERRORS", uiGreen
-	if total > 0 {
-		word, wc = fmt.Sprintf("%s ERRORS", commas(total)), uiRed
-	}
-	d.center(d.huge, bandY+(bandH-d.huge.cellH)/2, word, wc)
-
-	// Two tight blocks rather than rows spread over the whole panel, centred in
-	// what is left below the band.
-	lineH := d.grid.cellH + 4
-	sectionH := d.small.cellH + 10 + (1+len(dirs))*lineH
-	gap := 30
-	avail := fb.h - (bandY + bandH) - btnH - 2*uiMargin
-	y := bandY + bandH + 8 + (avail-2*sectionH-gap)/2
-
-	y = d.section(y, "RATE", "")
-	d.rightAt(colTxGbEnd, y, "TX Gb/s", uiDim)
-	d.rightAt(colTxPPSEnd, y, "TX pps", uiDim)
-	d.rightAt(colRxGbEnd, y, "RX Gb/s", uiDim)
-	d.rightAt(colRxPPSEnd, y, "RX pps", uiDim)
-	y += lineH
-	for i, dir := range dirs {
-		d.dirTag(dir, y)
-		v := views[i]
-		d.rightAt(colTxGbEnd, y, fmt.Sprintf("%.2f", v.txGbps), rateColor(v.txGbps, target))
-		d.rightAt(colTxPPSEnd, y, commas(roundPPS(v.txPPS)), uiFg)
-		d.rightAt(colRxGbEnd, y, fmt.Sprintf("%.2f", v.rxGbps), rateColor(v.rxGbps, target))
-		d.rightAt(colRxPPSEnd, y, commas(roundPPS(v.rxPPS)), uiFg)
-		y += lineH
-	}
-
-	y += gap
-	y = d.section(y, "OVERALL", cable)
-	d.rightAt(colFramesEnd, y, "frames", uiDim)
-	d.rightAt(colDataEnd, y, "data", uiDim)
-	d.rightAt(colLostEnd, y, "lost", uiDim)
-	d.rightAt(colLateEnd, y, "late", uiDim)
-	d.rightAt(colCRCEnd, y, "crc", uiDim)
-	d.rightAt(colKdropEnd, y, "kdrop", uiDim)
-	y += lineH
-	for i, dir := range dirs {
-		d.dirTag(dir, y)
-		v := views[i]
-		d.rightAt(colFramesEnd, y, commas(v.txFrames), uiFg)
-		d.rightAt(colDataEnd, y, humanBytes(v.txSent), uiFg)
-		d.rightAt(colLostEnd, y, commas(v.lost), errColor(v.lost))
-		d.rightAt(colLateEnd, y, commas(v.late), errColor(v.late))
-		d.rightAt(colCRCEnd, y, commas(v.crc), errColor(v.crc))
-		d.rightAt(colKdropEnd, y, commas(v.kdrop), errColor(v.kdrop))
-		y += lineH
-	}
+	x, w, y = d.panel(d.sincePanel, v.since, d.sinceH)
+	y = d.row(d.grid, x, w, y, "uptime", uptime(elapsed), uiFg)
+	y = d.row(d.grid, x, w, y, "frames", commas(v.rxFrames), uiFg)
+	y = d.row(d.grid, x, w, y, "data", humanBytes(v.rxGot), uiFg)
+	y = d.row(d.grid, x, w, y, "cable", cable, uiCyan)
+	d.errBlock(x, w, y+blockGap, v.since)
 
 	d.drawResetButton()
 	fb.flush()
 }
-
-func (d *display) section(y int, title, right string) int {
-	d.small.draw(d.fb, uiMargin, y, title, uiFg)
-	if right != "" {
-		d.right(d.small, d.cellX(colKdropEnd), y, right, uiCyan)
-	}
-	ruleY := y + d.small.cellH + 3
-	d.fb.rect(uiMargin, ruleY, d.fb.w-2*uiMargin, 1, uiRule)
-	return ruleY + 7
-}
-
-func (d *display) dirTag(dir *direction, y int) {
-	d.atBold(cellDirA, y, dir.tx.tag, uiCyan)
-	d.arrow(d.cellX(cellArrow), y+d.grid.cellH/2, uiDim)
-	d.atBold(cellDirB, y, dir.rx.tag, uiCyan)
-}
-
-// Drawn because the font has no arrow glyph. Occupies exactly one cell so the
-// grid is unaffected.
-func (d *display) arrow(x, y int, c rgb) {
-	w := d.grid.cellW
-	d.fb.rect(x, y-1, w-5, 2, c)
-	for i := 0; i < 6; i++ {
-		d.fb.rect(x+w-6+i, y-5+i, 1, 11-2*i, c)
-	}
-}