duckyPad-Pro

duckyScript Bytecode Virtual Machine

Details of duckyPad duckyScript 3 (DPDS3) instruction set, compiler, and binary format.

This is NOT the official implementation, which appears to be close-source.

I designed everything here myself from scratch.

Background

In duckyScript 1, it’s sufficient to simply parse line-by-line, as each line is independent.

duckyScript 3 introduced variables, IF statements, WHILE loops, and function calls.

Being much more complex, it makes sense to compile the script into bytecode and execute it on a virtual machine instead.

Virtual Stack Machine

DPDS3 VM is a simple stack machine with two stacks and a Program Counter (PC).

PC points to the current instruction being executed.
Arithmetic Stack: Used to perform calculations and store arguments.
Call Stack: Keeps track of function calls.

Compiled binary is loaded into memory, and PC starts executing at the beginning of the program.

Instruction Set

Each DPDS3 instruction has a fixed-length of three bytes.

First byte (Byte 0) is Opcode, specifying the action this instruction perform.
Second and third byte (Byte 1 and 2) provides optional data.
They are treated as one uint16_t or two uint8_t depending on the instruction.

Compiler

The DPDS3 compiler takes a text file and outputs a executable binary file.

The binary file should have extension .dsb (duckyScript binary).

Normally this is taken care of in the configurator. But you can also try it out on its own:

Download the source code
Unzip, and run with Python 3: python3 make_bytecode.py input output

Let’s say you have a simple script in sample_script.txt:

DEFINE TEN 10
VAR $spam = TEN*7+3
DELAY $spam

Compile with python3 make_bytecode.py sample_script.txt output.dsb

Compiled binary is written to output.dsb, along with some extra info:

--------- Program Listing After Preprocessing: ---------
1    VAR $spam = 10*7+3
2    DELAY $spam

--------- Assembly Listing, Unresolved ---------

PUSHC     10    0xa           ;VAR $spam = 10*7+3
PUSHC     7     0x7           ;VAR $spam = 10*7+3
MULT                          ;VAR $spam = 10*7+3
PUSHC     3     0x3           ;VAR $spam = 10*7+3
ADD                           ;VAR $spam = 10*7+3
POP       spam                ;VAR $spam = 10*7+3
PUSHI     spam                ;DELAY $spam
DELAY                         ;DELAY $spam
HALT

--------- Assembly Listing, Resolved ---------

0    PUSHC     10    0xa           ;VAR $spam = 10*7+3
3    PUSHC     7     0x7           ;VAR $spam = 10*7+3
6    MULT                          ;VAR $spam = 10*7+3
9    PUSHC     3     0x3           ;VAR $spam = 10*7+3
12   ADD                           ;VAR $spam = 10*7+3
15   POP       0     0x0           ;VAR $spam = 10*7+3
18   PUSHI     0     0x0           ;DELAY $spam
21   DELAY                         ;DELAY $spam
24   HALT



--------- Bytecode ---------
0x01 0x0a 0x00 0x01 0x07 0x00 0x11 0x00 0x00
0x01 0x03 0x00 0x0f 0x00 0x00 0x03 0x00 0x00
0x02 0x00 0x00 0x1b 0x00 0x00 0x08 0x00 0x00


Binary Size: 27 Bytes

Binary Executable

When a key is pressed, the corresponding .dsb file is loaded into bin_buf in ds3_vm.c. Execution occurs inside run_dsb() with execute_instruction().

Zero-terminated strings are stored at the end of the binary file.

Variables are stored in var_buf. Up to 64 variables can be declared.

CPU Instructions

All reference to “stack” refers to Arithmetic Stack. Unless noted otherwise.

Opcode Name	Byte 0 Decimal	Byte 0 Hex	Comment	Byte 1	Byte 2
NOP	0	0x0	Do nothing
PUSHC	1	0x1	Push a constant on stack	CONST_LSB	CONST_MSB
PUSHI	2	0x2	Push value at ADDR on stack	ADDR_LSB	ADDR_MSB
POP	3	0x3	Pop one item off top of stack Write it to ADDR	ADDR_LSB	ADDR_MSB
BRZ	4	0x4	Pop one item off top of stack If value is zero, jump to ADDR	ADDR_LSB	ADDR_MSB
JMP	5	0x5	Unconditional Jump	ADDR_LSB	ADDR_MSB
CALL	6	0x6	Jump to Subroutine Push PC+1 to call stack Jump to ADDR	ADDR_LSB	ADDR_MSB
RET	7	0x7	Return from Subroutine Pop one item off call stack Set PC to its value
HALT	8	0x8	Stop execution
VMVER	255	0xFF	VM Version		VM VER

Binary Operator Instructions

Binary as in involving two operands.

All instructions here:

Pop TWO items off arithmetic stack
First item is left-hand-side, second item is right-hand-side.
Perform operation
Push result back on stack.

Opcode Name	Byte 0 Decimal	Byte 0 Hex	Comment
EQ	9	0x9	Equal
NOTEQ	10	0xa	Not equal
LT	11	0xb	Less than
LTE	12	0xc	Less than or equal
GT	13	0xd	Greater than
GTE	14	0xe	Greater than or equal
ADD	15	0xf	Add
SUB	16	0x10	Subtract
MULT	17	0x11	Multiply
DIV	18	0x12	Integer division
MOD	19	0x13	Modulus
POW	20	0x14	Power of
LSHIFT	21	0x15	Logical left shift
RSHIFT	22	0x16	Logical right shift
BITOR	23	0x17	Bitwise OR
BITAND	24	0x18	Bitwise AND
LOGIAND	25	0x19	Logical AND
LOGIOR	26	0x1a	Logical OR

duckyScript Command Instructions

All reference to “stack” refers to Arithmetic Stack. Unless noted otherwise.

Opcode Name	Byte 0 Decimal	Byte 0 Hex	Comment	Byte 1	Byte 2
DELAY	27	0x1b	Pop one item off top of stack Delay the amount in milliseconds
KUP	28	0x1c	Release Key Pop ONE item Upper byte: KEYTYPE Lower byte: KEYCODE
KDOWN	29	0x1d	Press Key Pop ONE item Upper byte: KEYTYPE Lower byte: KEYCODE
MSCL	30	0x1e	Mouse Scroll Pop ONE item Scroll number of lines
MMOV	31	0x1f	Mouse Move Pop TWO items Move X and Y
SWCF	32	0x20	Switch Color Fill Pop THREE items Red, Green, Blue Set ALL LED color to the RGB value
SWCC	33	0x21	Switch Color Change Pop FOUR items N, Red, Green, Blue Set N-th switch to the RGB value If N is 0, set current switch.
SWCR	34	0x22	Switch Color Reset Pop one item off top of stack If value is 0, reset color of current key If value is between 1 and 15, reset color of that key If value is 99, reset color of all keys
STR	35	0x23	Print zero-terminated string at ADDR	ADDR_LSB	ADDR_MSB
STRLN	36	0x24	Same as above, presses ENTER at end
—-	37	0x25	Deprecated Do not use
OLC	38	0x26	OLED_CURSOR Pop TWO items X and Y
OLP	39	0x27	Print zero-terminated string at ADDR to OLED	ADDR_LSB	ADDR_MSB
OLU	40	0x28	OLED_UPDATE
OLB	41	0x29	OLED_CLEAR
OLR	42	0x2a	OLED_RESTORE
BCLR	43	0x2b	Clear switch event queue
PREVP	44	0x2c	Previous profile
NEXTP	45	0x2d	Next profile
GOTOP	46	0x2e	Pop one item Go to profile of its value
SLEEP	47	0x2f	Put duckyPad to sleep Terminates execution