alikberov / x80

x80(i8080) vs x86

🇷🇺	🇬🇧

x80 - i8080-PROperly

The RISC-Technology (Rebused Instruction Set Computer)

The story of tries to build a processor that has intuitive clear instruction set.

• Read the wikia
  • i8080 particulary support by commands (compactness, methods, simplicity)
  • i8086 particulary support by assembly (flexibility, pointers, registers)
  • i8080/i8086/z80 directly binary support is not provided by this project
• Try ▶️ online demo code

Main plan

• CPU-182:
  • 1-byte relative jumps (Jcnd $-128 .. $+127)
  • 8-bits APR (BH CH DH AL BL CL DL)
  • 16-bits pairs (BX CX DX)
  • 16-bits pointers (IP SP BP SI DI)
  • 16-bits of page RAM [0..65535]
• CPU-18x:
  • 08x - Null-bits ALU (experience factor)
  • 18x - 8-bits ALU
  • 28x - 16-bits ALU
  • 38x - 32-bits ALU
  • 48x - 64-bits ALU
• CPU-x82:
  • x80 - Null-modified realize (experience model)
  • x81 - First edition model
  • x82 - Second edition model
  • x83 - Thirth edition model
• CPU-284:
  • 2-bytes relative jumps (Jcnd $-32768 .. $+32767)
  • 16-bits APR (BH CH DH AL BL CL DL)
  • 32-bits pairs (BX CX DX)
  • 24-bits pointers (IP SP BP SI DI)
  • 24-bits of page RAM [0..16777215]
• CPU-386:
  • 3-bytes relative jumps (Jcnd $-8388608 .. $+8388607)
  • 32-bits APR (BH CH DH AL BL CL DL)
  • 64-bits pairs (BX CX DX)
  • 32-bits pointers (IP SP BP SI DI)
  • 32-bits of page RAM [up to 4 Gb]

No more any x86-crutches, like EAX or RIP. Register names has no changes, but changes binarity.

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Do You still thinking the i8080-architecture hopeless obsolete? And Z80 - the felicitous clone of i8080? Modern technologies allow to rebuild all i8080-software for new architecture with minimal difficulty. Let's try it!

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### Details ``` 00: HLT - It's alright, since NULL - is Final (of text file and any document) by logic; 80: NOP - Arithmetical -(-128) - is overflow and still returns the -128 anyway; FF: RET - Other Final, since 0xFF is rare code and finally of ordinary numbers. ``` :repeat_one: Representation for i8080-rudiment:

   ┌─►RET         Example:
Bx FF:Jcond $+1─┐ 1.RZ
┌──┘┌►Rcond     │ 2.RNZ
└───┴───────────┘ 3.RPO

🔁 Representation for x86-rudiment:

Bx FE:Jcond $+0─┐ 1.REPZ
↑ ┌►REPcond     │ 2.REPNZ
└─┴─────────────┘ 3.REPPO

🔂 Representation for internal functions as hollow calls:

   ┌─►RET         Example:
Bx FF:Ccond $+1─┐ 1.DAA
┌──┘┌► «Other»  │ 2.CLI/STI
└───┴───────────┘ 3.CPUID

🔁 Representation for complex functions as overflow calls:

Bx FE:Ccond $+0─┐ 1.WAIT
↑ ┌► «Complex»  │ 2.MUL/DIV
└─┴─────────────┘ 3.MOVS/CMPS

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Many of [:page_facing_up: Instructions Codes](http://htmlpreview.github.com/?http://github.com/Alikberov/x80/blob/master/emulator.html?instructions) aligned for maximal intuitive clear remembering:

Ax: Assign to registers / ALU-operations;
Bx: Branches by conditions;
Cx: Increments;
Dx: Decrements;
Fx: Functions.

✔️ Suitable solvings (for remembering):

AA: ALU - Adding          (ADD);
AC: ALU - Conjunction     (AND);
AD: ALU - Disjunction     (OR);
AE: ALU - Exclusive Or    (XOR);
... . . . . . . . . . . . . . .
BA: Branch if Altered sign (minus)
BB: Branch if Bigger (not minus)
BC: Branch if Carry
BD: Branch is "Discarry"
BE: Branch if Equal (Zero)
BF: Branch if Fictive (not equal)
... . . . . . . . . . . . . . .
CB: inCrement BX-pointer;
CC: inCrement CX-pointer;
DC: Decrement CX-pointer;
DD: Decrement DX-pointer;
... . . . . . . . . . . . . . .
CF: Carry Flag complement (CMC);
DF: Digits Flip over      (NOT);
EF: Envelope for Function (LOOP);
F0..F7: Function #n       (INT n);
FF: Function's Finish     (RET);

❔ Experimental solves:

   ┌──┬──┬──┬──┬──┬──┬──┬──┐
AH:│??│??│TF│WF│PF│SF│CF│ZF│
   └──┴──┴──┴──┴──┴──┴──┴──┘
Flags Register (AH - ALU Heap):
Bit 0:Zero  (Null is Zero);
Bit 1:Carry (1 bit to carrier);
Bit 2:Signed(n - 2n = -n);
Bit 4:Word  (1<<4 = 16 bits mode);
Bit 5:Trace (1<<5 = Thirty two);

❔ System сode particularity:

00: Prefix SS (not HLT);

Shifted ALU

Instruction set allow to do reverse ALU-operations with accumulator (SUB,SBB,CMP):

   5B   |SUB AL,BL   ; AL = AL - BL
   AB 7F|SUB AL,0x7F ; AL = AL - 0x7F
33 5B   |SUB DH,BL   ; DH = DH - BL
33 AB 7F|SUB DH,0x7F ; DH = DH - 0x7F
44 5B   |SUB BL      ; AL = BL - AL
44 AB 7F|SUB 0x7F    ; AL = 0x7F - AL
.. .. ..
   5F   |CMP AL,BL   ; Test(AL - BL)
   AF 7F|CMP AL,0x7F ; Test(AL - 0x7F)
33 5F   |CMP DH,BL   ; Test(DH - BL)
33 AF 7F|CMP DH,0x7F ; Test(DH - 0x7F)
44 5F   |CMP BL      ; Test(BL - AL)
44 AF 7F|CMP 0x7F    ; Test(0x7F - AL)

Since other reverse operations is nonsense (ADD,ADC,AND,OR,XOR), it working like comparators:

   5C   |AND AL,BL   ; AL = AL & BL
   AC 7F|AND AL,0x7F ; AL = AL & 0x7F
33 5C   |AND DH,BL   ; DH = DH & BL
33 AC 7F|AND DH,0x7F ; DH = DH & 0x7F
44 5C   |AND BL      ; Test(BL & AL)
44 AC 7F|AND 0x7F    ; Test(0x7F & AL)

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System Tricks

In/Out ports

All relative access by index pointers, where effective vector are escaped the 64K-bound, will processes like the in/out-ports.

        MOV  AL,[SP-1] ; Equal IN AL,255 if SP is 0x0000
        MOV  [SP+1],AL ; Equal OUT 1,AL if SP is 0xFFFF

Processors System Control

Processor haven't special instructions to control for inner states of unit. All PUSH/POP instructions provides access to internal register, when stack pointer aligned to bound of memory. When the SP sets in NULL or 0FFFFh, the PUSH/POP-instructions working without RAM, but with internal services registers of processor unit (debug register, task-context register, i8080-/z80-emulation). As a rule, supervisors process must to control this actions from applications and stop it any or making self.

	PUSH DX ; If SP is 0x0000, DX are writing to service registers
	PUSH AX ; Skip current service register
	POP  DX ; If SP is 0xFFFF, DX be readed from service registers
	POP  AX ; Skip current service register
	PUSH CX ; If SP is 0x0001, CX has indexing the page of service

Particulary, this is different way for access to in/out ports. In case, when services page included the hexadecimal capital ("A".."F"), it are disabled for application code as system page.