cz80: Add missing readme.txt with license information

Source:

https://github.com/RetroPie/pifba/blob/5edfa0d54303882eb72a4c13a22b369d61fde3a6/cpu/cz80/readme.txt

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+************************************************
+*                                              *
+*     CZ80 (Z80 CPU emulator) version 0.91     *
+*          Compiled with Dev-C++               *
+*  Copyright 2004-2005 Stéphane Dallongeville  *
+*                                              *
+************************************************
+
+CZ80 is a Z80 CPU emulator, priorities were given to :
+- code size
+- speed
+- accuracy
+- portablity
+
+It supports almost all undocumented opcodes and flags.
+
+The emulator can be freely distribued and used for any non commercial
+project as long you don't forget to credit me somewhere :)
+If you want some support about the CZ80, you can contact me on
+the Gens forum (http://gens.consolemul.com then go to the forum).
+
+
+You should find the following files in the emulation pack :
+- cz80.h          -> header file (prototypes, declarations...)
+- cz80.c          -> contains emulation core itself
+- cz80.inc        -> contains most used macros
+- cz80jmp.inc     -> Jump table definition when Jump Table used
+- cz80exec.inc    -> contains the major Cz80_Exec(...) function
+- cz80_op.inc     -> contains code for simple Z80 opcodes emulation
+- cz80_opCB.inc   -> contains code for CB prefixed Z80 opcodes emulation
+- cz80_opED.inc   -> contains code for ED prefixed Z80 opcodes emulation
+- cz80_opXY.inc   -> contains code for DD/FD prefixed Z80 opcodes emulation
+- cz80_opXYCB.inc -> contains code for DD/FD + CB prefixed Z80 opcodes emulation
+- readme.txt      -> the current file you're reading ;)
+
+
+* How compile the emulator ?
+****************************
+
+The emulator has been written with Dev-CPP 4.9.X.X
+You will maybe need to modify the u8, u16, u32, s8, s16, s32 and FASTCALL
+definitions (cz80.h) according to your C compiler and the target system.
+Then compile the cz80.c file, you should obtain a cz80.o (or cz80.obj) file...
+at this moment, you're ready to use the emulator just by linking the file in your project :)
+
+
+* How to use the emulator ?
+***************************
+
+1) Include the header file in your source :
+------------------------------------------
+
+#include "cz80.h"
+
+
+2) Init the CZ80 core :
+-----------------------
+
+If you want to use the internal CZ80 context offered :
+
+  Cz80_Init(&CZ80);
+
+but you can also define your own CZ80 context :
+
+  cz80_struc My_Z80;
+
+  ....
+
+  Cz80_Init(&My_Z80);
+
+
+You'll can emulate as many Z80 CPU as you want by defining severals CZ80 contexts.
+
+
+3) Set up your fetch region (where the Z80 will run code from) :
+----------------------------------------------------------------
+
+  Cz80_Set_Fetch(&CZ80, 0x0000, 0x7FFF, (u32) your_ROM);
+  Cz80_Set_Fetch(&CZ80, 0xA000, 0xFFFF, (u32) your_RAM);
+  ...
+
+
+4) Set up your memory (where the Z80 will read and write data) :
+----------------------------------------------------------------
+
+  Cz80_Set_ReadB(&CZ80, your_z80readbyte_function);
+  Cz80_Set_WriteB(&CZ80, your_z80readbyte_function);
+
+You can improve CZ80 performance by using WORD read/write function.
+For that, you need to enable the 'CZ80_USE_WORD_HANDLER' define in cz80.h file.
+In this case, you'll need to add that :
+
+#if CZ80_USE_WORD_HANDLER
+  Cz80_Set_ReadW(&CZ80, your_z80readword_function);
+  Cz80_Set_WriteW(&CZ80, your_z80readword_function);
+#endif
+
+Your read function need to be of CZ80_READ type :
+typedef u32  FASTCALL CZ80_READ(u32 adr);
+
+Your write function need to be of CZ80_WRITE type :
+typedef void FASTCALL CZ80_WRITE(u32 adr, u32 data);
+
+
+5) Set Up your port (where the Z80 will read and write IO data) :
+-----------------------------------------------------------------
+
+  Cz80_Set_INPort(&CZ80, your_z80readport_function);
+  Cz80_Set_OUTPort(&CZ80, your_z80writport_function);
+
+Your readPort function need to be of CZ80_READ type :
+typedef u32  FASTCALL CZ80_READ(u32 adr);
+
+Your writePort function need to be of CZ80_WRITE type :
+typedef void FASTCALL CZ80_WRITE(u32 adr, u32 data);
+
+
+6) Set Up your interrupt callback function :
+--------------------------------------------
+
+  Cz80_Set_IRQ_Callback(&CZ80, your_z80irqcallback_function);
+
+Your IRQ callback function need to be of CZ80_INT_CALLBACK type :
+typedef s32  FASTCALL CZ80_INT_CALLBACK(s32 param);
+
+If you don't understand what i am talking about here, just ignore...
+it's not needed in almost case.
+
+
+6) Set Up your RETI callback function :
+---------------------------------------
+
+  Cz80_Set_RETI_Callback(&CZ80, your_z80reticallback_function);
+
+Your RETI callback function need to be of CZ80_RETI_CALLBACKtype :
+typedef void FASTCALL CZ80_RETI_CALLBACK();
+
+Again, if you don't understand what i am talking about here, ignore...
+
+
+7) Reset the CZ80 core before fisrt use :
+-----------------------------------------
+
+  Cz80_Reset(&CZ80);
+
+
+8) Do some cycles :
+-------------------
+
+Then it's time to really do some work, if you want to execute 1000 cycles, just do :
+
+  cycles_done = Cz80_Exec(&CZ80, 1000);
+
+Cz80_Exec function return the number of cycles actually done.
+Since each instruction take more than 1 cycle, Cz80_Exec will execute a bit more than
+you requested, for instance here, it can return 1008 cycles instead of 1000.
+In this case, adjust the number of cycle to do like that :
+
+  cycles_by_frame = 4800;
+  extra_cycles = 0;
+  while (true)
+  {
+     ...
+     extra_cycles = CZ80_Exec(&CZ80, cycles_by_frame - extra_cycles) - cycles_by_frame;
+     ...
+  }
+
+If Cz80_Exec returns a negatif value, an error occured.
+
+
+9) Do an interrupt request :
+----------------------------
+
+  Cz80_Set_IRQ(&CZ80, 0);
+
+or for a NMI :
+
+  Cz80_Set_NMI(&CZ80);
+
+
+10) Cancel an interrupt request :
+---------------------------------
+
+  Cz80_Clear_IRQ(&CZ80);
+
+or for a NMI :
+
+  Cz80_Clear_NMI(&CZ80);
+
+
+
+* Switchs
+*********
+
+There are severals switchs in the cz80.h file which permit you to configure
+CZ80 depending your needs.
+
+- CZ80_FETCH_BITS (default = 4)
+
+This defines the number of bits to select fetch region.
+This value must be 4 <= X <= 12
+Greater value offers permit to have more fetch region.
+In almost case, 4 is enough, but if you have fetch region smaller than 0x1000 bytes,
+increase this value.
+
+- CZ80_LITTLE_ENDIAN
+
+Define the endianess of the target platform.
+x86 CPU use Little Endian.
+
+- CZ80_USE_JUMPTABLE
+
+Set it to 1 to use Jump table instead of big case statement.
+This can bring some small speed improvemen.
+Be careful, some compiler doesn't support (computed label) so it's
+saffer to not use it.
+
+- CZ80_SIZE_OPT
+
+Add some extras optimisation for the code size versus speed.
+Minor changes anyway...
+
+- CZ80_USE_WORD_HANDLER
+
+See the "Set Up Memory" section for more détail.
+
+- CZ80_EXACT
+
+Enable accurate emulation of extended undocumented opcode and flags.
+minor speed decrease when activated.
+Even without that flag, CZ80 is already uite accurate, keep it
+disable unless you need it or if speed isn't important for you.
+
+- CZ80_DEBUG
+
+Used by me, keep it disable :p
+
+
+
+* History
+*********
+
+Version 0.90 :
+--------------
+
+* Initial release for debugging purpose ^^