diff --git a/src/common/ecs/binpack.ts b/src/common/ecs/binpack.ts
new file mode 100644
index 00000000..a0662cc9
--- /dev/null
+++ b/src/common/ecs/binpack.ts
@@ -0,0 +1,170 @@
+
+var debug = true;
+
+export interface BoxConstraints {
+    left?: number;
+    top?: number;
+    width: number;
+    height: number;
+    box?: PlacedBox;
+}
+
+enum BoxPlacement {
+    TopLeft=0, TopRight=1, BottomLeft=2, BottomRight=3
+}
+
+export interface Box {
+    left: number;
+    top: number;
+    right: number;
+    bottom: number;
+}
+
+export interface PlacedBox extends Box {
+    bin: Bin;
+    parent: Box;
+    place: BoxPlacement;
+}
+
+function boxesIntersect(a: Box, b: Box) : boolean {
+    return !(b.left >= a.right || b.right <= a.left || b.top >= a.bottom || b.bottom <= a.top);
+}
+
+function getBoxPlacements(b: PlacedBox) {
+    let posns : BoxPlacement[];
+    let snugw = b.right - b.left == b.parent.right - b.parent.left;
+    let snugh = b.bottom - b.top == b.parent.bottom - b.parent.top;
+    if (snugw && snugh) {
+        posns = [BoxPlacement.TopLeft];
+    } else if (snugw && !snugh) {
+        posns = [BoxPlacement.TopLeft, BoxPlacement.BottomLeft];
+    } else if (!snugw && snugh) {
+        posns = [BoxPlacement.TopLeft, BoxPlacement.TopRight];
+    } else {
+        posns = [BoxPlacement.TopLeft, BoxPlacement.TopRight,
+            BoxPlacement.BottomLeft, BoxPlacement.BottomRight];
+    }
+    return posns;
+}
+
+export class Bin {
+    boxes: Box[] = [];
+    free: Box[] = [];
+
+    constructor(public readonly binbounds: Box) {
+        this.free.push(binbounds);
+    }
+    getBoxes(bounds: Box, limit: number) : Box[] {
+        let result = [];
+        for (let box of this.boxes) {
+            //console.log(bounds, box, boxesIntersect(bounds, box))
+            if (boxesIntersect(bounds, box)) {
+                result.push(box);
+                if (result.length >= limit) break;
+            }
+        }
+        return result;
+    }
+    fits(b: Box) {
+        if (!boxesIntersect(this.binbounds, b)) return false;
+        if (this.getBoxes(b, 1).length > 0) return false;
+        return true;
+    }
+    bestFit(b: Box) : Box | null {
+        let bestscore = 0;
+        let best = null;
+        for (let f of this.free) {
+            let dx = (f.right - f.left) - (b.right - b.left);
+            let dy = (f.bottom - f.top) - (b.bottom - b.top);
+            if (dx >= 0 && dy >= 0) {
+                let score = 1 / (1 + dx + dy);
+                if (score > bestscore) {
+                    best = f;
+                }
+            }
+        }
+        return best;
+    }
+    add(b: PlacedBox) {
+        if (debug) console.log('added',b.left,b.top,b.right,b.bottom);
+        if (!this.fits(b)) {
+            //console.log('collided with', this.getBoxes(b, 1));
+            throw new Error(`bad fit ${b.left} ${b.top} ${b.right} ${b.bottom}`)
+        }
+        // add box to list
+        this.boxes.push(b);
+        // delete bin
+        let i = this.free.indexOf(b.parent);
+        if (i < 0) throw new Error('cannot find parent');
+        if (debug) console.log('removed',b.parent.left,b.parent.top,b.parent.right,b.parent.bottom);
+        this.free.splice(i, 1);
+        // split into new bins
+        switch (b.place) {
+            case BoxPlacement.TopLeft:
+                this.addFree( { top: b.top, left: b.right, bottom: b.bottom, right: b.parent.right } );
+                this.addFree( { top: b.bottom, left: b.parent.left, bottom: b.parent.bottom, right: b.parent.right } );
+                break;
+            case BoxPlacement.TopRight:
+                this.addFree( { top: b.top, left: b.parent.left, bottom: b.bottom, right: b.left } );
+                this.addFree( { top: b.bottom, left: b.parent.left, bottom: b.parent.bottom, right: b.parent.right } );
+                break;
+            case BoxPlacement.BottomLeft:
+                this.addFree( { top: b.parent.top, left: b.parent.left, bottom: b.top, right: b.parent.right } );
+                this.addFree( { top: b.top, left: b.right, bottom: b.parent.bottom, right: b.parent.right } );
+                break;
+            case BoxPlacement.BottomRight:
+                this.addFree( { top: b.parent.top, left: b.parent.left, bottom: b.top, right: b.parent.right } );
+                this.addFree( { top: b.top, left: b.parent.left, bottom: b.parent.bottom, right: b.left } );
+                break;
+        }
+    }
+    addFree(b: Box) {
+        if (b.bottom > b.top && b.right > b.left) {
+            if (debug) console.log('free',b.left,b.top,b.right,b.bottom);
+            this.free.push(b);
+        }
+        // TODO: merge free boxes
+    }
+}
+
+export class Packer {
+    bins : Bin[] = [];
+    boxes : BoxConstraints[] = [];
+
+    pack() : boolean {
+        for (let bc of this.boxes) {
+            let box = this.bestPlacement(bc);
+            if (!box) return false;
+            box.bin.add(box);
+            bc.box = box;
+        }
+        return true;
+    }
+    bestPlacement(b: BoxConstraints) : PlacedBox | null {
+        let left = b.left != null ? b.left : 0;
+        let top = b.top != null ? b.top : 0;
+        let right = left + b.width;
+        let bottom = top + b.height;
+        for (let bin of this.bins) {
+            let place : BoxPlacement = BoxPlacement.TopLeft; //TODO
+            let box = { left, top, right, bottom };
+            let parent = bin.bestFit(box);
+            if (parent) {
+                box.left = parent.left;
+                box.top = parent.top;
+                box.right = parent.left + b.width;
+                box.bottom = parent.top + b.height;
+                /*
+                if (place == BoxPlacement.BottomLeft || place == BoxPlacement.BottomRight) {
+                    box.top = parent.bottom - (box.bottom - box.top);
+                }
+                if (place == BoxPlacement.TopRight || place == BoxPlacement.BottomRight) {
+                    box.left = parent.right - (box.right - box.left);
+                }
+                */
+                return { parent, place, bin, ...box };
+            }
+        }
+        return null;
+    }
+}
diff --git a/src/common/ecs/ecs.ts b/src/common/ecs/ecs.ts
index 40e1a31f..a810d2b6 100644
--- a/src/common/ecs/ecs.ts
+++ b/src/common/ecs/ecs.ts
@@ -107,6 +107,11 @@ export interface Query extends SourceLocated {
     limit?: number;
 }
 
+export class SystemStats {
+    tempstartseq: number | undefined;
+    tempendseq: number | undefined;
+}
+
 export interface System extends SourceLocated {
     name: string;
     actions: Action[];
@@ -117,6 +122,10 @@ export const SELECT_TYPE = ['once', 'foreach', 'join', 'with', 'if', 'select'] a
 
 export type SelectType = typeof SELECT_TYPE[number];
 
+export class ActionStats {
+    callcount: number = 0;
+}
+
 export interface ActionBase extends SourceLocated {
     select: SelectType;
     event: string;
@@ -687,6 +696,7 @@ class ActionEval {
         if (isNaN(tempinc)) throw new ECSError(`bad temporary offset`, this.action);
         if (!this.sys.tempbytes) throw new ECSError(`this system has no locals`, this.action);
         if (tempinc < 0 || tempinc >= this.sys.tempbytes) throw new ECSError(`this system only has ${this.sys.tempbytes} locals`, this.action);
+        this.scope.updateTempLiveness(this.sys);
         return `${this.tmplabel}+${tempinc}`;
         //return `TEMP+${this.scope.tempOffset}+${tempinc}`;
     }
@@ -828,10 +838,13 @@ export class EntityScope implements SourceLocated {
     systems: System[] = [];
     entities: Entity[] = [];
     fieldtypes: { [name: string]: 'init' | 'const' } = {};
+    sysstats = new Map<System, SystemStats>();
+    actionstats = new Map<Action, ActionStats>();
     bss = new UninitDataSegment();
     rodata = new ConstDataSegment();
     code = new CodeSegment();
     componentsInScope = new Set();
+    eventSeq = 0;
     tempOffset = 0;
     tempSize = 0;
     maxTempBytes = 0;
@@ -861,6 +874,7 @@ export class EntityScope implements SourceLocated {
         return entity;
     }
     addUsingSystem(system: System) {
+        if (!system) throw new Error();
         this.systems.push(system);
     }
     getEntityByName(name: string) {
@@ -1063,9 +1077,12 @@ export class EntityScope implements SourceLocated {
         let systems = this.em.event2systems[event];
         if (!systems || systems.length == 0) {
             // TODO: error or warning?
-            console.log(`warning: no system responds to "${event}"`); return '';
             //throw new ECSError(`warning: no system responds to "${event}"`);
+            console.log(`warning: no system responds to "${event}"`);
+            return '';
         }
+        this.eventSeq++;
+        // generate code
         let s = this.dialect.code();
         //s += `\n; event ${event}\n`;
         systems = systems.filter(s => this.systems.includes(s));
@@ -1089,6 +1106,7 @@ export class EntityScope implements SourceLocated {
                     s += this.dialect.comment(`end action ${sys.name} ${event}`);
                     // TODO: check that this happens once?
                     codeeval.end();
+                    this.getActionStats(action).callcount++;
                     numActions++;
                 }
             }
@@ -1102,6 +1120,32 @@ export class EntityScope implements SourceLocated {
         this.maxTempBytes = Math.max(this.tempSize, this.maxTempBytes);
         if (n < 0) this.tempOffset = this.tempSize;
     }
+    getSystemStats(sys: System) : SystemStats {
+        let stats = this.sysstats.get(sys);
+        if (!stats) {
+            stats = new SystemStats();
+            this.sysstats.set(sys, stats);
+        }
+        return stats;
+    }
+    getActionStats(action: Action) : ActionStats {
+        let stats = this.actionstats.get(action);
+        if (!stats) {
+            stats = new ActionStats();
+            this.actionstats.set(action, stats);
+        }
+        return stats;
+    }
+    updateTempLiveness(sys: System) {
+        let stats = this.getSystemStats(sys);
+        let n = this.eventSeq;
+        if (stats.tempstartseq && stats.tempendseq) {
+            stats.tempstartseq = Math.min(stats.tempstartseq, n);
+            stats.tempendseq = Math.max(stats.tempendseq, n);
+        } else {
+            stats.tempstartseq = stats.tempendseq = n;
+        }
+    }
     includeResource(symbol: string): string {
         this.resources.add(symbol);
         return symbol;
@@ -1116,8 +1160,9 @@ export class EntityScope implements SourceLocated {
         let isMainScope = this.parent == null;
         this.tempOffset = this.maxTempBytes = 0;
         let start;
-        if (isMainScope) {
-            this.addUsingSystem(this.em.getSystemByName('Init')); //TODO: what if none?
+        let initsys = this.em.getSystemByName('Init');
+        if (isMainScope && initsys) {
+            this.addUsingSystem(initsys); //TODO: what if none?
             start = this.generateCodeForEvent('main_init');
         } else {
             start = this.generateCodeForEvent('start');
@@ -1127,6 +1172,15 @@ export class EntityScope implements SourceLocated {
             let code = this.generateCodeForEvent(sub);
             this.code.addCodeFragment(code);
         }
+        //this.showStats();
+    }
+    showStats() {
+        for (let sys of this.systems) {
+            console.log(sys.name, this.getSystemStats(sys));
+        }
+        for (let action of Array.from(this.actionstats.keys())) {
+            console.log(action.event, this.getActionStats(action));
+        }
     }
     dump(file: SourceFileExport) {
         this.analyzeEntities();
diff --git a/src/test/testecs.ts b/src/test/testecs.ts
index 2498062d..fcc31534 100644
--- a/src/test/testecs.ts
+++ b/src/test/testecs.ts
@@ -1,7 +1,8 @@
 import assert from "assert";
-import { execFileSync } from "child_process";
+import { execFileSync, spawnSync } from "child_process";
 import { readdirSync, readFileSync, writeFileSync } from "fs";
 import { describe } from "mocha";
+import { Bin, Packer } from "../common/ecs/binpack";
 import { ECSCompiler } from "../common/ecs/compiler";
 import { Dialect_CA65, EntityManager, SourceFileExport } from "../common/ecs/ecs";
 
@@ -389,8 +390,24 @@ describe('Compiler', function() {
         let goodtxt = readFileSync(destpath, 'utf-8');
         if (outtxt.trim() != goodtxt.trim()) {
             writeFileSync('/tmp/' + goodfn, outtxt, 'utf-8');
-            execFileSync('/usr/bin/diff', [srcpath, destpath]);
+            console.log(spawnSync('/usr/bin/diff', [srcpath, destpath], {encoding:'utf-8'}).stdout);
             throw new Error(ecsfn + ' did not match test file');
         }
     });
 });
+
+describe('Box Packer', function() {
+    it('Should pack boxes', function() {
+        let packer = new Packer();
+        let bin1 = new Bin({ left:0, top:0, right:10, bottom:10 });
+        packer.bins.push(bin1);
+        packer.boxes.push({ width: 5, height: 5 });
+        packer.boxes.push({ width: 5, height: 5 });
+        packer.boxes.push({ width: 5, height: 5 });
+        packer.boxes.push({ width: 5, height: 5 });
+        if (!packer.pack()) throw new Error('cannot pack')
+        console.log(packer.boxes);
+        console.log(packer.bins[0].free)
+    });
+});
+