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TinyBasic

This is a simple TinyBASIC interpreter designed for use on microcontrollers

Language supports the most basic commands like LET, PRINT, GOTO, IF and INPUT, 26 single-letter variables are available to the programmer, despite these limitations the language is Turing complete allowing to create (almost) any simple program.

Code memory space, expression tokens limit, maximum line number and shell IO communication way can be configured. No printfs are used (except for the debug stuff), that allows to change the communication method to for example microcontroller's UART module.

POKE and PEEK command can be disabled when used on PC, as they always cause segmentation fault, and SAVE and LOAD can be disabled when used on a MCU that doesn't have access to file system.

In case infinite loop occures there is a way to kill the execution by sending any key to the console. Execution is stopped and there is no problem with loosing progress having to reset the MCU. (KILL_IO must be enabled.)

List of the supported commands

Keywords and variable names are case-insensitive.

BASIC commands
  • LET <variable> = <expression>
    Assigns the result of an expression to the given variable, LET keyword isn't necessary and format <var> = <expr> will also be understood.
  • PRINT <"string"> : <expression>
    Prints out strings and expression results to the console, : token can be used as a separator to for example put a value after a string, leaving the separator token at the end of the line disables the linefeed that would have been sent at the end of the line.
  • CHAR <variable>
    Print a character in the given variable (equivalent to C's putchar())
  • GOTO <line number>
    This command jumps to the given line number.
  • IF <expression> <comparison> <expression> THEN <command>
    Executes the command after the THEN keyword if the comparison result is true, available comparisons are the following: equal (=), not equal (<>), lower than (<) and greater than (>)
  • INPUT <variable>
    Gets the expression from the console and put it into the specified variable.
  • REM <comment>
    Do nothing, only purpose of this command is to store comments
  • CLEAR
    Clears the console and homes the cursor.
  • LIST
    Lists the program.
  • MEMORY
    Shows how much code memory is left.
  • RUN
    Starts the program from the first line.
  • NEW
    Clears the code memory after confirmation.
POKE_PEEK commands
  • POKE <address expression>, <value expression>
    Sets the memory at the given address to the given value
  • PEEK <address expression>, <variable>
    Gets the memory from the given address and stores it in the given variable.
  • POKEB <address expression>, <value expression>
    Same as POKE but only accesses uint8_t instead of peek_t
  • PEEKB <address expression>, <variable>
    Same as POKE but only accesses uint8_t instead of peek_t
FILE_IO commands
  • SAVE <filename>
    Saves memory contents.
  • LOAD <filename>
    Loads memory contents.

Expression solving

Supported operations

Language interpreter contains a simple expression solver supporting basic integer arythmetic operations like: add (+), subtract (-), multiply (*), divide (/) and remainder (%). Basic logic functions are also supported: AND (&), OR (|), XOR (^) and NOT (!).

Operation precedence
Precedence Operation Operator(s)
1 Subexpressions in brackets ()
2 Unary operators +, -, !
3 Important arythmetics *, /, %
4 Low importance arythmetics +, -
5 Logic operations &, |, ^
Literal formats
Name Format Examples
Variable Single letter variable name A, B, c, z, Z
Decimal Normal value starting with non-zero digit 0, 1, 2, 420, 1024, 911
Hexadecimal Hex value starting with 0x prefix 0x45, 0xFF, 0xDEADBEEF
Octal Value starting with '0' prefix 033, 0377, 0105, 00
Binary Value starting with '0b' prefix 0b0110, 0b1001, 0b01010101

Configuration

Defines
  • NEWLINE - Character that will be interpreted as a new line.
  • BACKSPACE - Character that will be interpreted as a backspace.
  • CODE_MEMORY_SIZE - Size of the program memory.
  • EXPR_MAX_TOKENS - Size of expression solver buffer.
  • MAX_LINUENUM - Maximum valid line number (not including MAX_LINENUM).
  • POKE_PEEK - Enable POKE and PEEK commands.
  • FILE_IO - Enable SAVE and LOAD commands.
  • IO_KILL - Enable breaking the execution if new characters were received during execution.
  • LOOPBACK - Enable cosole loopback (input characters will be sent back).
Data types
  • line_t - Format in which line number is stored.
  • var_t - Format in which variables are stored.
  • uvar_t - Unisgned version of the format in which variables are stored.
  • peek_t - Format in which POKE and PEEK accesses memory.
IO Defines

In the definitions x is the pointer to the data that has to be sent, received or checked.

  • IO_INIT - Called at the start of main() starts up the IO device.
  • PUTCHAR(x) - Prints the x character to the IO device.
  • GETCHAR(x) - Return character from the IO device.
  • IO_CHECK(x) - Returns if there are any new characters in IO (used for IO_KILL).

Example configs

PC
#define NEWLINE           '\n'
#define BACKSPACE         '\b'
#define CODE_MEMORY_SIZE  8192
#define EXPR_MAX_TOKENS   64
#define MAX_LINENUM       10000
#define POKE_PEEK         0
#define FILE_IO           1
#define IO_KILL           0
#define OUTPUT_CRLF       0
#define SHORT_STRING      0
#define LOOPBACK          0

typedef uint16_t          line_t;
typedef int32_t           var_t;
typedef uint32_t          uvar_t;
typedef size_t            peek_t;

#define IO_INIT()         ((void)0)
#define PUTCHAR(x)        (putchar(*x))
#define GETCHAR(x)        (*x = getchar())
#define IO_CHECK(x)       (*x = false)
AVR (ATmega328)
#define NEWLINE           '\n'
#define BACKSPACE         '\b'
#define CODE_MEMORY_SIZE  512
#define EXPR_MAX_TOKENS   16
#define MAX_LINENUM       10000
#define POKE_PEEK         1
#define FILE_IO           0
#define IO_KILL           1
#define CRLF              1
#define SHORT_STRING      1
#define LOOPBACK          0

typedef uint16_t          line_t;
typedef int32_t           var_t;
typedef uint32_t          uvar_t;
typedef size_t            peek_t;

#define F_CPU 16000000UL
#define __AVR_ATmega328__
#include <avr/io.h>

#define IO_INIT() {              \
  UBRR0 = F_CPU / 8 / 9600 - 1;  \
  UCSR0A = 1<<U2X0;              \
  UCSR0B = 1<<TXEN0 | 1<<RXEN0;  \
}

#define PUTCHAR(x) {               \
  while (!(UCSR0A & (1<<UDRE0)));  \
  UDR0 = *x;                       \
}

#define GETCHAR(x) {              \
  while (!(UCSR0A & (1<<RXC0)));  \
  *x = UDR0;                      \
}

#define IO_CHECK(x) {           \
  *x = !!(UCSR0A & (1<<RXC0));  \
}
Arduino (any, tested on ESP8266)

In case of different board memory size might need to be adjusted and in case of some boards (ESP8266 for example), int main(void) might need to be replaced with void setup(void) and void loop(void) might need to get added.

#define NEWLINE           '\r'
#define BACKSPACE         '\b'
#define BACKSPACE_STR     "\b \b"
#define CODE_MEMORY_SIZE  512
#define EXPR_MAX_TOKENS   16
#define MAX_LINENUM       10000
#define POKE_PEEK         0
#define FILE_IO           0
#define IO_KILL           1
#define OUTPUT_CRLF       1
#define SHORT_STRING      1
#define LOOPBACK          1

typedef uint16_t          line_t;
typedef int32_t           var_t;
typedef uint32_t          uvar_t;
typedef size_t            peek_t;

#define IO_INIT()         (Serial.begin(115200))
#define PUTCHAR(x)        (Serial.write(*x))
#define GETCHAR(x)        { while (!Serial.available()); *x = Serial.read(); }
#define IO_CHECK(x)       (*x = Serial.available())

Example programs

Primes generator
10 REM Primes generator, get all primes up to max prime
20 PRINT "Enter max prime: ":
30 INPUT C
40 A = 2
50 GOTO 90
60 A = A + 1
70 IF A < C + 1 THEN GOTO 50
80 END
90 B = 2
100 IF A % B = 0 THEN GOTO 60
110 B = B + 1
120 IF B < A / 2 THEN GOTO 100
130 PRINT A
140 GOTO 60
Fibonacci Sequence
10 REM Fibonacci Sequence
20 A = 1
30 B = 1
40 C = 20
50 PRINT A
60 D = A
70 A = A + B
80 B = D
90 C = C - 1
100 IF C > 0 THEN GOTO 50
Base Converter
10 REM Base Converter
20 PRINT "Enter a value: ":
30 INPUT A
40 PRINT ""
50 PRINT "Decimal:       " : A
60 B = A
70 C = 32
80 PRINT "Binary:        ":
90 IF B & 0x80000000 <> 0 THEN PRINT "1":
100 IF B & 0x80000000  = 0 THEN PRINT "0":
110 B = B * 2
120 C = C - 1
130 IF C > 0 THEN GOTO 90
140 PRINT ""
150 B = A
160 C = 8
170 PRINT "Hexadecimal:   ":
180 D = (B / 268435456 & 0xF) + 0x30
190 IF D > 0x39 THEN D = D + 0x7
200 CHAR D
210 B = B * 16
220 C = C - 1
230 IF C > 0 THEN GOTO 180
240 PRINT ""
250 B = A
260 C = 10
270 PRINT "Octal:         ":
280 D = (B / 1073741824 & 0x3) + 0x30
290 CHAR D
300 D = (B / 134217728 & 0x7) + 0x30
310 CHAR D
320 B = B * 8
330 C = C - 1
340 IF C > 0 THEN GOTO 300
350 PRINT ""
360 PRINT ""