diff --git a/Makefile b/Makefile
index a4cb6d0..2faf4af 100644
--- a/Makefile
+++ b/Makefile
@@ -4,13 +4,13 @@ F_CPU=16000000
 
 TARGET=menelaus
 
-USB_DEVICE=/dev/ttyACM0
+USB=/dev/ttyACM0
 
 build: $(TARGET).hex
 
 upload: $(TARGET).hex
-	while [ ! -r $(USB_DEVICE) ]; do sleep 1; done; \
-	avrdude -p $(MCU) -c avr109 -U flash:w:$(TARGET).hex -P $(USB_DEVICE)
+	while [ ! -r $(USB) ]; do sleep 1; done; \
+	avrdude -p $(MCU) -c avr109 -U flash:w:$(TARGET).hex -P $(USB)
 
 test: ; racket test.rkt
 
diff --git a/README.md b/README.md
index a6cfcd3..863a1b3 100644
--- a/README.md
+++ b/README.md
@@ -4,6 +4,31 @@ A firmware for the
 [Atreus](http://atreus.technomancy.us) keyboard, written in
 [Microscheme](https://ryansuchocki.github.io/microscheme/).
 
+## Features
+
+* 6KRO (6 simultaneous keys, not including modifiers)
+* Software debouncing
+* Multiple layers (limited only by memory)
+* Bind arbitrary Scheme functions to a key
+* Combo keys (a single keystroke can send a modifier and a non-modifier)
+
+## Usage
+
+Replace `/dev/ttyACM0` with the path your OS assigns to the USB
+bootloader of the microcontroller:
+
+    $ make upload USB=/dev/ttyACM0
+
+Currently only the "multidvorak" layout is supported.
+
+## Development
+
+The firmware can also be run on a PC rather than on the
+microcontroller in the keyboard using `test.rkt` which loads it up
+into Racket and simulates the GPIO functions with a test harness:
+
+    $ make test
+
 ## License
 
 Copyright © 2014-2019 Phil Hagelberg and contributors
diff --git a/keycodes.scm b/keycodes.scm
index fd01419..fefad1b 100644
--- a/keycodes.scm
+++ b/keycodes.scm
@@ -48,6 +48,7 @@
 (define key-home 74)
 (define key-end 77)
 (define key-insert 73)
+(define key-delete 76)
 
 (define key-semicolon 51)
 (define key-comma 54)
@@ -71,6 +72,23 @@
 (define key-vol-up 128)
 (define key-vol-down 129)
 
+(define key-f1 58)
+(define key-f2 59)
+(define key-f3 60)
+(define key-f4 61)
+(define key-f5 62)
+(define key-f6 63)
+(define key-f7 64)
+(define key-f8 65)
+(define key-f9 66)
+(define key-f10 67)
+(define key-f11 68)
+(define key-f12 69)
+
+(define key-printscreen 70)
+(define key-scroll-lock 71) ; lol
+(define key-pause 72)
+
 (define (modifier? keycode) (list? keycode))
 (define (modify keycode) (list keycode))
 (define (unmodify keycode) (car keycode))
@@ -83,3 +101,5 @@
 (define mod-shift (modify #x02))
 (define mod-alt (modify #x04))
 (define mod-super (modify #x08))
+
+(define (sft keycode) (combo mod-shift keycode)) ; shorthand
diff --git a/layout.scm b/layout.scm
index cd4ab09..1c5a1e8 100644
--- a/layout.scm
+++ b/layout.scm
@@ -14,7 +14,15 @@
 (define (set-layer-0)
   (set! current-layer (vector-ref layers 0)))
 
-(vector-set!
+(define (set-layer-hard)
+  (set! current-layer (vector-ref layers 3)))
+
+(define (reset)
+  #f) ;; TODO: uh, seriously. I need this. how.
+
+;;;; layers
+
+(vector-set! ; base
  layers 0
  (vector key-q key-w key-e key-r key-t key-backslash
          key-y key-u key-i key-o key-p
@@ -28,23 +36,58 @@
          key-esc key-tab mod-super mod-shift key-backspace mod-alt
          key-space fn key-quote key-left-bracket key-enter))
 
-(vector-set!
+(vector-set! ; fn
  layers 1
- (vector (combo mod-shift key-1) (combo mod-shift key-2) key-up
-         (combo mod-shift key-dash) (combo mod-shift key-equal)
-         0 key-page-up key-7 key-8 key-9 (combo mod-shift key-8)
+ (vector (sft key-1) (sft key-2) key-up (sft key-dash) (sft key-equal) 0
+         key-page-up key-7 key-8 key-9 (sft key-8)
 
-         (combo mod-shift key-3) key-left key-down key-right
-         (combo mod-shift key-4) 0
-         key-page-down key-4 key-5 key-6 (combo mod-shift key-right-bracket)
+         (sft key-3) key-left key-down key-right (sft key-4) 0
+         key-page-down key-4 key-5 key-6 (sft key-right-bracket)
 
-         key-dash key-equal (combo mod-shift key-9)
-         (combo mod-shift key-0) (combo mod-shift key-7) mod-ctrl
+         key-dash key-equal (sft key-9) (sft key-0) (sft key-7) mod-ctrl
          key-backtick key-1 key-2 key-3 key-backslash
 
          set-layer-2 key-insert mod-super mod-shift key-backspace mod-alt
          key-space fn key-e key-0 key-right-bracket))
 
-(vector-set!
- layers 2 ; TODO
- (vector 0))
+(vector-set! ; l2 (function keys, etc)
+ layers 2
+ (vector key-insert key-home key-up key-end key-page-up 0
+         key-up key-f7 key-f8 key-f9 key-f10
+
+         key-delete key-left key-down key-right key-page-down 0
+         key-down key-f4 key-f5 key-f6 key-f11
+
+         0 key-vol-up 0 0 reset mod-ctrl
+         set-layer-hard key-f1 key-f2 key-f3 key-f12
+
+         0 key-vol-down mod-super mod-shift key-backspace mod-alt
+         key-space set-layer-0 key-printscreen key-scroll-lock key-pause))
+
+(vector-set! ; hard dvorak
+ layers 3
+ (vector key-quote key-comma key-period key-p key-y key-backslash
+         key-f key-g key-c key-r key-l
+
+         key-a key-o key-e key-u key-i key-backtick
+         key-d key-h key-t key-n key-s
+
+         key-semicolon key-q key-j key-k key-x mod-ctrl
+         key-b key-m key-w key-v key-z
+
+         key-esc key-tab mod-super mod-shift key-backspace mod-alt
+         key-space fn key-quote key-left-bracket key-enter))
+
+(vector-set! ; hard dvorak fn
+ layers 4
+ (vector (sft key-1) (sft key-2) key-up (sft key-left-bracket) (sft key-right-bracket) 0
+         key-page-up key-7 key-8 key-9 (sft key-8)
+
+         (sft key-3) key-left key-down key-right (sft key-4) 0
+         key-page-down key-4 key-5 key-6 (sft key-equal)
+
+         key-left-bracket key-right-bracket (sft key-9) (sft key-0) (sft key-7) mod-ctrl
+         key-backtick key-1 key-2 key-3 key-backslash
+
+         set-layer-2 key-insert mod-super mod-shift key-backspace mod-alt
+         key-space fn key-e key-0 key-right-bracket))