TINY 8086

TINY 8086 is an interpreter written in assembly 8086 for the Tiny Basic language

The goal is to produce a flat binary that can run without the need of a OS on any x86 machine

---

THE INTERPRETER

---

• The interpreter can execute single instructions or an entire program

• It is possible to store a program of a maximum of 255 lines

• There are available 26 numeric variables identified by the letters A,B,C...Z

---

BASE COMMANDS

---

• LIST : print on screen the content of the stored program

• RUN : execute the program currently stored in memory

• RESET : entire reset of the interpreter (memory, variables,etc..)

---

INSTRUCTIONS

---

PRINT

• allow to print on screen : numbers,expressions,variables,strings and their combinations

• to concatenate elements use the "," character

PRINT 123
--> print "123"

PRINT (4*5)+6
--> print "26"

PRINT A
--> print the numeric value stored in A

PRINT "hello"
--> print hello

PRINT "2+3 is :",2+3
--> print "2+3 is 5"

---

END

• Terminate the execution of the current running program

10 PRINT "hello" 
20 END						
--> print "hello" and terminate

10 PRINT "line1"
20 END
30 PRINT "line2"		
--> print "line1" and terminate

---

LET variable = expression

• Change the content of a variable (A,B,C...Z)
• Variables can store integers numbers between -32767 and +32767

LET A = 69 
--> store in A the value 69

LET A = 5*2 
--> store in A the value 10

LET A = A+1 
--> increase the value of A by 1

LET A = B+C 
--> store in A the sum B+C

LET A = (B+C) 
--> store in A the sum B+C

---

INPUT variable

• Read a number from the terminal and store in the designated variable
• Multiple reads are possible using the "," character

INPUT A
--> read a number and store it in A

INPUT A,B,C
--> read 3 numbers and store them in A,B,C

---

IF condition THEN instruction

• If the condition is true then execute the instruction following THEN
• Logical operators supported : ==,!=,<,>,<=,>=

IF 2!=1 THEN PRINT "hello"
--> always print "hello"

IF A<(3*4) THEN PRINT "hello""
--> print "hello" only if the content of the variable A is less than 12

---

GOTO expression

• Continue the execution of the program at the line indicated by the expression

GOTO 25
--> continue the execution at line 25

10 PRINT "hello"
20 GOTO 10
30 END
--> print "hello" repeatedly (does not terminate)

---

GOSUB expression and RETURN

• Execute the instructions from the line indicated by the expression up to RETURN
• It resumes the execution of the program at the line following the starting GOSUB

10 PRINT "line1"
20 GOSUB 100
30 END
100 PRINT "line2"
110 RETURN
--> print "line1", "line2" and terminate

---

REM

• It is possible to insert line of comment using the "REM" prefix

10 REM Test program
20 PRINT "hello"
30 END
 --> print "hello" and terminate

---

EXAMPLES

---

Sample code for loops

10 LET A=0
20 IF A>=5 THEN GOTO 60
30 PRINT "hello"
40 LET A=A+1
50 GOTO 20
60 END
--> print "hello" 5 times

10 LET A=0
20 PRINT "hello"
30 LET A=A+1
40 IF A<5 THEN GOTO 20
50 END 
--> print "hello" 5 times

---

Sample calculator program

5 PRINT "CALCULATOR"
10 PRINT "Operation:"
20 PRINT "1 : sum"
30 PRINT "2 : subtraction"
40 PRINT "3 : multiplication"
50 PRINT "4 : division"
60 INPUT A
70 IF A<1 THEN END
80 IF A>4 THEN END
90 PRINT "Insert the first number:"
100 INPUT B
110 PRINT "Insert the second number:"
120 INPUT C
130 PRINT "Result:"
140 IF A==1 THEN PRINT B+C
150 IF A==3 THEN PRINT B-C
160 IF A==4 THEN PRINT B*C
170 IF A==3 THEN PRINT B/C 
180 GOTO 10

---

IMPLEMENTATION DETAILS

Interpreter

• The system consists of a program (the interpreter itself) and a boot loader (whose only job is to load the program into memory).

• The memory it is structured as :

             ________
0000:0000   |BOOT    |  
            |        |--7C00 boot loader start
            |        |
0000:FFFF   |________|

             ________
1000:0000   |STACK   |  
            |        |
            |        |
1000:FFFF   |________|--FFFF stack base

             ________
2000:0000   |PROGRAM |--0000 program start
            |        |
            |        |
2000:FFFF   |________|

---

SOURCE CODE

• BOOT.ASM : the boot loader

• UTILS.ASM : utilities functions

• FLOPPY.ASM : to create a floppy image of the system

• ILM.ASM : the interpreter

• ILM/*.ASM : folder containing all the functions required by the interpreter

---

BUILD AND RUN

This repository contains all the tools needed to build and run the system.

• BUILD.BAT will invoke the Nasm assembler to produce in the BUILD folder the following files : boot.bin, program.bin and floppy.img

• RUN.BAT will invoke the Bochs emulator to run the system from floppy.img

---

FOLDERS

• SRC : source code
• BUILD : output directory
• DOC : Tiny Basic and Assembly 8086 documentation
• NASM : Nasm assembler
• BOCHS : Bochs emulator

---

REFERENCES

• TINY BASIC : http://www.ittybittycomputers.com/IttyBitty/TinyBasic/DDJ1/Design.html

• ASM 8086 : http://vitaly_filatov.tripod.com/ng/asm/

• NASM : https://www.nasm.us/

• BOCHS : https://bochs.sourceforge.io/

---

NOTES

• The current keymap is set to US