diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..45a2cfc
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "liblzg"]
+	path = liblzg
+	url = https://github.com/mbitsnbites/liblzg.git
diff --git a/Makefile b/Makefile
index f9fc98b..19040d8 100644
--- a/Makefile
+++ b/Makefile
@@ -1,18 +1,21 @@
 .POSIX:
 
 ASM=$(wildcard src/*.asm)
-RES=res.bin/amour.sid res.bin/levels.bin
-
-ifeq "$(CARTRIDGE)" "1"
-	FORMAT:=3
-else
-	FORMAT:=1
-endif
+RES=res.bin/amour.sid res.bin/levels.bin res.bin/unlzg.bin
 
 .PHONY: debug env clean
 
-bin/snake.prg: env $(ASM) $(RES) bin/explodefont
-	dasm src/main.asm -Isrc/ -DSYSTEM=64 -DDEBUG=$(DEBUG) -DVERBOSE=$(VERBOSE) -DCARTRIDGE=$(CARTRIDGE) -f$(FORMAT) -sbuild/symbols.txt -obin/snake.prg
+bin/snake.bin: bin/snake.pack.lz
+	dasm src/cart.asm -DVERBOSE=$(VERBOSE) -f3 -sbuild/cart.symbols.txt -obin/snake.bin
+
+bin/snake.pack: env $(ASM) $(RES) bin/explodefont
+	dasm src/main.asm -Isrc/ -DSYSTEM=64 -DDEBUG=$(DEBUG) -DVERBOSE=$(VERBOSE) -DCARTRIDGE=$(CARTRIDGE) -f3 -sbuild/pack.symbols.txt -obin/snake.pack
+
+bin/snake.pack.lz: bin/snake.pack liblzg/src/tools/lzg
+	liblzg/src/tools/lzg bin/snake.pack > bin/snake.pack.lz
+
+liblzg/src/tools/lzg:
+	cd liblzg/src && make
 
 clean:
 	rm -rf {build,bin,res.bin}
@@ -29,6 +32,9 @@ res.bin/amour.sid:
 res.bin/levels.bin: bin/level res.org/levels.txt
 	bin/level < res.org/levels.txt > res.bin/levels.bin
 
+res.bin/unlzg.bin:
+	cp res.org/unlzg.bin res.bin/unlzg.bin
+
 bin/level: util/rlevel.cpp
 	g++ -o bin/level util/rlevel.cpp
 
diff --git a/README.md b/README.md
index 7d42f23..039b6a7 100644
--- a/README.md
+++ b/README.md
@@ -19,19 +19,25 @@ You can also define the following environment variables:
 
 ```$ VERBOSE=1 make```      output useful info during compilation
 
-```$ CARTRIDGE=1 make```    produces an 8K bin ready to be burnt to an *PROM
-
 ## Developer docs
+### Package
+The whole program is assembled into a ```snake.pack``` binary blob with the following structure.
+
+Absolute    | Offset      | Description
+------------|-------------|------------
+```$1000``` | ```$0000``` | load address
+```$2800``` | ```$1800``` | entry point (start address)
+
 ### Memory map
 Address               | PRG   | Description
 ----------------------|-------|------------
 ```$0000 - $0001```   | no    | hardware
 ```$0002 - $00FF```   | no    | zero page pointers
-```$0100 - $07FF```   | no    | *free ram*
-```$0800 - $0FFF```   | yes   | autostart (BASIC or cartridge) + Low Program Segment
-```$1000 - $1FFF```   | yes   | SID tune + Middle Program Segment
+```$0100 - $01FF```   | no    | stack page
+```$0200 - $07FF```   | no    | *free ram*
+```$1000 - $1FFF```   | yes   | SID tune
 ```$2000 - $27FF```   | yes   | custom char
-```$2800 - $xxxx```   | yes   | High Program Segment (only needed part used)
+```$2800 - $xxxx```   | yes   | Program segment (only needed part used)
 ```$xxxx - $CCFF```   | no    | *free ram*
 ```$CD00 - $CDFF```   | no    | data segment (not-initialized vars)
 ```$CE00 - $CEFF```   | no    | list X
@@ -39,9 +45,14 @@ Address               | PRG   | Description
 ```$D000 - $DFFF```   | no    | I/O
 ```$E000 - $FFFF```   | no    | Kernal
 
-Note: program (code) segments have been put in all possible free spots in order to squeeze the game into an 8K cartridge.
+### Compression
+```snake.pack``` is compressed into ```snake.pack.lz``` using [liblzg](https://github.com/mbitsnbites/liblzg), to save space in order to fit the game in a *PROM.
 
-### Custom charset
+### Decompression
+```cart.asm``` is located at ```$8000``` (standard org address for C64 cartridges), and contains the decompression routine and the ```snake.pack.lz```. It decompresses ```snake.pack.lz``` back to ```$1000```, and jumps to its entry point at ```$2800```.
+
+### Miscellanea
+#### Custom charset
 Index           | Description
 ----------------|-------------
 ```$00 - $1F``` |   A-Z (space first)
@@ -50,8 +61,3 @@ Index           | Description
 ```$50 - $5F``` |   hex digits, reversed
 ```$60 -    ``` |   game tiles
 
-### Cartridge
-Cartridge version is at $8000 and simply copies itself back at $800.
-
-Cartridge version can not be built with DEBUG=1 flag due to size constraints.
-
diff --git a/liblzg b/liblzg
new file mode 160000
index 0000000..182b56c
--- /dev/null
+++ b/liblzg
@@ -0,0 +1 @@
+Subproject commit 182b56cb36843720f38eff2ec30db1deac4e85bd
diff --git a/res.org/unlzg.bin b/res.org/unlzg.bin
new file mode 100644
index 0000000..b6a6bda
Binary files /dev/null and b/res.org/unlzg.bin differ
diff --git a/src/cart.asm b/src/cart.asm
index 8126107..8e3e92c 100644
--- a/src/cart.asm
+++ b/src/cart.asm
@@ -1,15 +1,21 @@
-#if VERBOSE = 1
-LASTINIT SET .
-#endif
+    processor 6502
+
+    SEG cartridgeSegment
+    org $8000
 
 cartridge SUBROUTINE
-
-    WORD #$8009
-    WORD #$801a
+    WORD .coldstart
+    WORD .warmstart
 
     ; CBM80 in PETSCII (cartridge signature for autostart)
     BYTE #$c3,#$c2,#$cd,#$38,#$30
 
+.unlzg:
+    INCBIN "res.bin/unlzg.bin"
+
+.lzpack:
+    INCBIN "bin/snake.pack.lz"
+
 .coldstart:
     sei
     stx $d016
@@ -20,28 +26,29 @@ cartridge SUBROUTINE
     cli
 
 .warmstart:
-    ; Copy cartridge content into proper memory location
-    ldx #$20
-    lda #$0
-    tay
-    sta srcPointer
-    sta dstPointer
-    lda #>cartridgeStart
-    sta srcPointer + 1
-    lda #$08
-    sta dstPointer + 1
-.loop:
-    lda (srcPointer),y
-    sta (dstPointer),y
-    iny
-    bne .loop
-    inc srcPointer + 1
-    inc dstPointer + 1
-    dex
-    bne .loop
+    ; address of input compressed data
+    lda #<.lzpack
+    sta 26
+    lda #>.lzpack
+    sta 27
+
+    ; address of output decompressed data
+    lda #$00
+    sta 28
+    lda #$10
+    sta 29
+    jsr .unlzg
+
+    ; jump to program entry
+    jmp $2800
 
-    jmp start
 
 #if VERBOSE = 1
-    ECHO "cart.asm @ ",LASTINIT,"len:",(. - LASTINIT)
-#endif
\ No newline at end of file
+    ECHO "8k CARTRIDGE SIZE:",(. - $8000),"=",[(. - $8000)d]
+    ECHO "SPACE LEFT:",($9fff - .),"=",[($9fff - .)d]
+#endif
+
+    ; force filler for the *PROM
+. = $9fff
+    BYTE #$ff
+
diff --git a/src/main.asm b/src/main.asm
index e8daa60..6269d38 100644
--- a/src/main.asm
+++ b/src/main.asm
@@ -20,34 +20,6 @@
     ECHO "End of zeropage variables. Space left: ",($90 - .)
 #endif
 
-; Initialized segments
-; ----------------------------------------------------------------------
-    SEG autostartSegment
-#if CARTRIDGE = 0
-    org $801
-    INCLUDE "basic.asm" ; BASIC _MUST_ stay at this address
-#else
-    org $800
-    INCLUDE "cart.asm"
-#endif
-    INCLUDE "initdata.asm"
-
-; Program "Segment" Low
-; ----------------------------------------------------------------------
-; You just have to fill this empty space, don't you think so? ;-)
-    INCLUDE "game.asm"
-    INCLUDE "gameover.asm"
-    INCLUDE "introreset.asm"
-    INCLUDE "program.asm"
-    INCLUDE "subroutines.asm"
-    INCLUDE "levels.asm"
-    INCLUDE "intro1.asm"
-; Note: some code had to be included at an higher address
-
-#if VERBOSE = 1
-    ECHO "End of Low Program Segment. Space left:",($1000 - .)
-#endif
-
 ; SID tune (previously properly cleaned, see HVSC)
 ; ----------------------------------------------------------------------
     SEG sidSegment
@@ -55,13 +27,7 @@
 sidtune:
     INCBIN "../res.bin/amour.sid"
 #if VERBOSE = 1
-    ECHO "End of SIDtune at ",.
-#endif
-    INCLUDE "multicolor.asm"
-    INCLUDE "levelreset.asm"
-    INCLUDE "outro.asm"
-#if VERBOSE = 1
-    ECHO "End of Middle Program Segment. Space left:",($2000 - .)
+    ECHO "End of SIDtune at ",.,"Space left:",($2000 - .)
 #endif
 
 ; Font Data
@@ -72,30 +38,26 @@ sidtune:
 tggsFont:
     INCLUDE "tggs.asm"
 
-; Program Segment High
+; Program Segment
 ; ----------------------------------------------------------------------
-
+    SEG programSegment
+    org $2800
+    INCLUDE "program.asm"
+    INCLUDE "initdata.asm"
+    INCLUDE "game.asm"
+    INCLUDE "gameover.asm"
+    INCLUDE "introreset.asm"
+    INCLUDE "subroutines.asm"
+    INCLUDE "levels.asm"
+    INCLUDE "intro1.asm"
+    INCLUDE "multicolor.asm"
+    INCLUDE "levelreset.asm"
+    INCLUDE "outro.asm"
 #if VERBOSE = 1
-    ECHO "End of High Program Segment at: ",.,"Space left:",($cd00 - .)
+    ECHO "End of program segment at:",.
+    ECHO "PACK SIZE:",(. - $1000),"=",[(. - $1000)d]
 #endif
 
-#if VERBOSE = 1
-#if CARTRIDGE = 0
-    ; +2 because of PRG header
-    ECHO "PRG size:",([. - $801 + 2]d),"dec"
-#else
-    ECHO "BIN size:",([. - $800]d),"dec"
-#endif
-#endif
-
-; Uninitialized segments
-; ----------------------------------------------------------------------
-; Cartridge locations
-; -------------------
-    SEG.U cartridgeSegment
-    org $8000
-cartridgeStart:
-
 ; Data variables
 ; -----------------
     SEG.U dataSegment
@@ -113,10 +75,8 @@ listX DS 256
 listY DS 256
 
 ;
-; coded during december 2017
+; coded 2017, 2018, 2019, 2020
 ; by giomba -- giomba at glgprograms.it
 ; this software is free software and is distributed
 ; under the terms of GNU GPL v3 license
 ;
-
-; vim: set expandtab tabstop=4 shiftwidth=4: