1.
Ignacio Burgueño
Lua Workshop 2015
Stockholm, Sweden
At the end of the rainbow

2.
About Me
Ignacio Burgueño
Developer at inConcert
@iburgueno
https://github.com/ignacio

3.
What will be talking about?
● Writing a ZX Spectrum emulator in Lua 5.3
● Fun with Bitwise operators

4.
A bit of history

5.
Fairlight
Bo Jangeborg, 1985

6.
What is needed?
● Replace hardware parts with software
● Which parts?

7.
Architecture
https://commons.wikimedia.org/wiki/File:ZXspectrum_mb.jpg

8.
Architecture
"ZX Spectrum block diagram" taken from the book “The ZX Spectrum ULA” by Chris Smith

9.
Memory

10.
CPU
"Z80 arch" by Appaloosa - Own work. Licensed under CC BY-SA 3.0 via Commons -
https://commons.wikimedia.org/wiki/File:Z80_arch.svg#/media/File:Z80_arch.svg
Instruction
Register
Instruction
Decoder
Control
Logic
I R
1+_ 1+_
MUXMUX
W ZW' Z'
BB' CC'
DD' EE'
H LH' L'
IX
IY
PC
SP
TEMP
ACU
A
A'
F
F'
+
BUFFERSBUFFERSBUFFERS
ALU
Internal Data Bus 8 Bit
Address Bus 16 Bit
Control Bus
Control Section
Z80 Architecture

11.
CPU

12.
CPU – Instruction Set
● 8-bit arithmetic and logic operations
● 16-bit arithmetic
● 8-bit load
● 16-bit load
● Bit set, reset, and test
● Call, return, and restart
● Exchange, block transfer, and search
● General purpose arithmetic and CPU control
● Input and output
● Jump
● Rotate and shift LD A,42 0x3e 0x2a

13.
CPU – Fetch/Execute Cycle

14.
CPU – Fetch/Execute Cycle

15.
CPU – Fetch/Execute Cycle

16.
CPU – Fetch/Execute Cycle

17.
CPU - Opcodes

18.
CPU – Instruction families
● Same operation is applied to different registers
● One instruction for each combination
● Avoid writing the same function over and over
● Generate them using a template

19.
CPU – Instruction families

20.
CPU – Instruction families

21.
CPU – Instruction families

22.
See what's going on

23.
Drawing to the Screen

24.
Drawing to the Screen

25.
Drawing to the Screen

26.
Drawing to the Screen

27.
Drawing to the Screen
luasdl2
https://github.com/Tangent128/luasdl2
More information on the subject:
How "oldschool" graphics worked video series

28.
Getting software in it
(aka, how do I load games on this?)

29.
Parsing Binary data
Offset (bytes) Size Description
0 1 byte I
1 8 words HL', DE', BC', AF'
9 10 words HL, DE, BC, IY, IX
19 1 byte Interrupt
20 1 byte R
21 4 words AF, SP
25 1 byte Interruption Mode
26 1 byte Border Color
27 49152 bytes RAM dump 16384 .. 65535
Total: 49179 bytes
File Formats - SNA

30.
File Formats - SNA
● Parsing binary formats
● Don't want to split strings
● Enter string.unpack

31.
File Formats - SNA
● Cumbersome to read
● What value ends up where?
● Extend the unpack format string

32.
File Formats - SNA

33.
File Formats - SNA

34.
Testing
● Run little code snippets
● Make sure registers have the correct values
● Correct memory locations are read and written at the
right times

35.
Testing
● Run little code snippets
● Make sure registers have the correct values
● Correct memory locations are read and written at the
right times

36.
Demo

37.
Where to get it?
https://github.com/ignacio/luagleck
Where do I get software to try?
http://www.worldofspectrum.org/archive.html

38.
Thank you!
Any questions?
Ignacio Burgueño - @iburgueno