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- ___________________________________________________________________________
- DrZ80 (c) Copyright 2004 Reesy. Free for non-commercial use
- Reesy's e-mail: drsms_reesy(atsymbol)yahoo.co.uk
- Replace (atsymbol) with @
-
- ___________________________________________________________________________
- What is it?
- -----------
- DrZ80 is an emulator for the Z80 microprocessor, written in ARM 32-bit assembly.
- It is aimed at chips such as ARM7 and ARM9 cores, StrongARM and XScale, to interpret Z80
- code as fast as possible.
- Flags are mapped onto ARM flags whenever possible, which speeds up the processing of an opcode.
- ARM Register Usage
- ------------------
- See source code for up to date of register usage, however a summary is here:
- r0-3: Temporary registers
- r3 : Pointer to Opcode Jump table
- r4 : T-States remaining
- r5 : Pointer to Cpu Context
- r6 : Current PC + Memory Base (i.e. pointer to next opcode)
- r7 : Z80 A Register in top 8 bits (i.e. 0xAA000000)
- r8 : Z80 F Register (Flags) (NZCV) in lowest four bits
- r9 : Z80 BC Register pair in top 16 bits (i.e. 0xBBCC0000)
- r10 : Z80 DE Register pair in top 16 bits (i.e. 0xDDEE0000)
- r11 : Z80 HL Register pair in top 16 bits (i.e. 0xHHLL0000)
- r12 : Z80 Stack + Memory Base (i.e. pointer to current stack in host system memory)
- ( note: r3,r12 are always preserved when calling external memory functions )
- How to Compile
- --------------
- The core is targeted for the GNU compiler, so to compile just add the "DrZ80.o" object
- to your makefile and that should be it.
- If you want to compile it seperately, use: as -o DrZ80.o DrZ80.s
- ( note: If you want to use DrZ80 with a different compiler you will need to run
- some sort of parser through the source to make the syntax of the source
- compatible with your target compiler )
- Adding to your project
- ----------------------
- To add DrZ80 to your project, add DrZ80.o, and include DrZ80.h
- There is one structure: 'struct DrZ80', and three functions: DrZ80Run,DrZ80RaiseInt
- and DrZ80_irq_callback.
- Don't worry if this seem very minimal - its all you need to run as many Z80s as you want.
- It works with both C and C++.
- ( Note: DrZ80_irq_callback is just a pointer to an irq call back function that needs
- to be written by you )
- Declaring a Memory handlers
- ---------------------------
- Before you can reset or execute Z80 opcodes you must first set up a set of memory handlers.
- There are 8 functions you have to set up per CPU, like this:
- unsigned int z80_rebaseSP(unsigned short new_sp);
- unsigned int z80_rebasePC(unsigned short new_pc);
- unsigned char z80_read8(unsigned short a);
- unsigned short z80_read16(unsigned short a);
- void z80_write8(unsigned char d,unsigned short a);
- void z80_write16(unsigned short d,unsigned short a);
- unsigned char z80_in(unsigned char p);
- void z80_out(unsigned char p,unsigned char d);
-
- You can think of these functions representing the Z80's memory bus.
- The Read and Write functions are called whenever the Z80 reads or writes memory.
- The In and Out functions are called whenever the Z80 uses the I/O ports.
- The z80_rebasePC and z80_rebaseSP functions are to do with creating direct memory
- pointers in the host machines memory, I will explain more about this later.
- Declaring a CPU Context
- -----------------------
- To declare a CPU simple declare a struct Cyclone in your code. For example to declare
- two Z80s:
- struct DrZ80 MyCpu;
- struct DrZ80 MyCpu2;
- It's probably a good idea to initialise the memory to zero:
- memset(&MyCpu, 0,sizeof(MyCpu));
- memset(&MyCpu2,0,sizeof(MyCpu2));
- Next point to your memory handlers:
- MyCpu.z80_rebasePC=z80_rebasePC;
- MyCpu.z80_rebaseSP=z80_rebaseSP;
- MyCpu.z80_read8 =z80_read8;
- MyCpu.z80_read16 =z80_read16;
- MyCpu.z80_write8 =z80_write8;
- MyCpu.z80_write16 =z80_write16;
- MyCpu.z80_in =z80_in;
- MyCpu.z80_out =z80_out;
- Now you are nearly ready to reset the Z80, except you need one more function: checkpc().
- The z80_rebasePC() function
- ---------------------------
- When DrZ80 reads opcodes, it doesn't use a memory handler every time, this would be
- far too slow, instead it uses a direct pointer to ARM memory.
- For example if your Rom image was at 0x3000000 and the program counter was $206,
- Cyclone's program counter would be 0x3000206.
- The difference between an ARM address and a Z80 address is also stored in a variable called
- 'pc_membase'. In the above example it's 0x3000000. To retrieve the real PC, DrZ80 just
- subtracts 'pc_membase'.
- Everytime the Z80 PC is modified, i.e. by a jump,branch intructions or by an interupt, DrZ80
- calls the z80_rebasePC function. If the PC is in a different bank, for example Ram instead
- of Rom, change 'pc_membase', recalculate the new PC and return it.
- The z80_rebaseSP() function
- ---------------------------
- When DrZ80 pushs/pops to the Z80 stack pointer, it doesn't use a memory handler every time. In
- order to gain more speed a direct pointer to ARM memory is used. For example if your Ram was at
- 0x3000000 and the z80 stack pointer counter was 0xD000, DrZ80's stack pointer would be 0x300D000.
- The difference between an ARM address and a Z80 address is also stored in a variable called
- 'sp_membase'. In the above example it's 0x3000000. To retrieve the real SP, DrZ80 just
- subtracts 'sp_membase'.
- Everytime the Z80 SP is modified ( i.e. set with a new value LD SP,NN etc ) DrZ80
- calls the z80_rebaseSP function. If the SP is in a different bank, for example Rom instead
- of Ram, change 'sp_membase', recalculate the new SP and return it.
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