SD-8516 Technical Manual

The Stellar Dynamics SD-8516 represents a categorical reimagining of microprocessor architecture. This 16-bit CPU, implemented in AssemblyScript for the VC-3 computer system, delivers performance exceeding conventional silicon constraints through advanced cross-boundary resonance microcascades.

Key Specifications:

• 16-bit architecture with 16 general-purpose registers
• Clock speed: 10-20 MHz (targeting 3-5 MIPS)
• Memory: 256KB addressable via 4-bank system
• ~20× performance improvement over legacy 8510 design

Since the days of the first minicomputers, Stellar Dynamics has been at the forefront of microarchitecture design. The SD-8516 is not simply an iteration upon its predecessors; it is a categorical reimagining of what a “processor” can be when unshackled from quantum locality.

While our earliest designs struggled with resonance cascade instability, the SD-8516 delivers stable, predictable cross-boundary resonance microcascades at clock rates exceeding the theoretical limits of conventional silicon.

These advancements position the Stellar Dynamics SD-8516 as the definitive architecture for next-generation computation: a bridge between classical logic engines and the emergent technologies of multidimensional processing.

The SD-8516 features sixteen 16-bit registers:

Note: The SD-8516 does not use register pairing except for multiplication operations, which store results in the AB register pair.

Registers are encoded as 4-bit values (0-15), allowing two registers per byte:

• Low nibble: First operand
• High nibble: Second operand

Example: ADD A, B encodes as 0x01 (A=0, B=1)

The 16-bit FLAGS register contains:

Arithmetic Flags (Byte 1):

• Bit 0: Z (Zero) - Result was zero
• Bit 1: N (Negative) - Result was negative (bit 15 set)
• Bit 2: C (Carry) - Unsigned overflow/borrow
• Bit 3: V (Overflow) - Signed overflow
• Bits 4-7: Reserved

Control Flags (Byte 2):

• Bit 8: H (Halt) - CPU stopped, waiting for interrupt
• Bit 9: T (Trace) - Single-step debugging mode
• Bit 10: B (Breakpoint) - Breakpoint mode active
• Bit 11: E (Exception) - Sticky error flag
• Bit 12: P (Protected) - Protected mode enabled
• Bit 13: I (Interrupt) - Interrupt enable/disable
• Bit 14: S (Sound) - Sound System Interrupt enable
• Bit 15: Reserved

Layout: Z N C V - - - - H T B E P I S -

The SD-8516 supports 4 banks of 64KB each (256KB total) through special addressing modes:

LDA [I:J]        ; Load from bank I, offset J
STA [2:$1000]    ; Store to bank 2, offset $1000

Bank allocation:

• Bank 0: System RAM, program space
• Bank 1: Audio samples and sound registers
• Bank 2: Primary video framebuffer + palette
• Bank 3: Secondary video buffer (high-resolution modes)

Examples:

LDA #$1234       ; Load immediate $1234 into A
LDAL #$42        ; Load immediate byte $42 into AL
LDA [$F000]      ; Load word from address $F000
STA [2:$1000]    ; Store A to bank 2, offset $1000

The SD-8516 is paired with the SD-450 sound subsystem, featuring 4 independent voices with ADSR envelopes.

Each voice occupies 16 bytes of memory in Bank 1:

Voice base addresses:

• Voice 0: $ED00
• Voice 1: $ED10
• Voice 2: $ED20
• Voice 3: $ED30

Gate register values:

• 0: Silent (gate off)
• 1: Square wave
• 2: Triangle wave
• 3: Sawtooth wave
• 4: Sine wave
• 5: Pulse wave (variable width via DATA1)
• 6: White/pink/brown noise (type via DATA1)

The Attack-Decay-Sustain-Release envelope shapes each note:

• Attack: Time to reach peak volume (0-255 × 10ms)
• Decay: Time to decay to sustain level (0-255 × 10ms)
• Sustain: Held volume level (0.0-1.0 of peak)
• Release: Time to fade to silence after gate off (0-255 × 10ms)

Example:

; Play middle C on voice 0
LDA $112B           ; C4 frequency (262 Hz / 0.0596)
STA [$ED00]         ; FREQ_LO/HI
LDAL $01            ; Square wave
STAL [$ED02]        ; GATE
LDAL $4D            ; ~30% volume
STAL [$ED03]        ; VOLUME

The VC-3 supports both text and graphics modes:

Mode 1 (40×25):

• Character buffer: $F000-$F3E7 (1000 bytes)
• Color buffer: $F800-$FBE7 (1000 bytes)
• Character ROM: $E800-$E8FF (256 characters × 8 bytes)

Color byte format: (bg_color << 4) | fg_color

Mode 2 (80×25):

• Same layout, 2000 bytes each
• Scanline doubling for 640×400 output

Mode 3 (320×200×16):

• Framebuffer: Bank 2, $00000-$07CFF (32,000 bytes)
• Palette: Bank 2, $F000-$F02F (16 colors × 3 bytes RGB)
• Pixel packing: 2 pixels per byte (high/low nibbles)

Pixel addressing:

offset = (y × 160) + (x ÷ 2)
address = Bank 2 + offset

Mode 4 (256×224×256):

• Framebuffer: Bank 2, $00000-$DFFFF (57,344 bytes)
• Palette: Bank 2, $F000-$F2FF (256 colors × 3 bytes RGB)
• 1 byte per pixel (256 colors)

Each palette entry is 3 bytes (RGB): Offset +0: Red (0-255) Offset +1: Green (0-255) Offset +2: Blue (0-255)

The KERNAL ROM provides system services at $E000:

GETKEY - Read keyboard buffer IN: None OUT: A = ASCII character (if available) B = previous buffer count

WRITE_CHAR - Write character to screen IN: A = character code X = column (0-39/79) Y = row (0-24)

WRITE_STRING - Write null-terminated string IN: A = string address (low byte) B = string address (high byte) X = column Y = row

CTOXY - Move cursor IN: X = column Y = row

GETCURSOR - Read cursor position OUT: X = column Y = row

STRLEN - Get string length IN: A = string address (low byte) B = string address (high byte) OUT: A = length (low byte) B = length (high byte) C = carry flag if > 256 bytes

BYTETOSTR - Convert byte to decimal string IN: A = byte value (0-255) X = destination address (low) Y = destination address (high) OUT: Zero-terminated string at XY

• ARR_LEFT - Move cursor left (bounded)
• ARR_RIGHT - Move cursor right (bounded)
• ARR_UP - Move cursor up (bounded)
• ARR_DOWN - Move cursor down (bounded)

Labels:

loop:               ; Define label
    JMP @loop       ; Reference label with @

Immediates:

LDA #$1234          ; Hexadecimal
LDA #100            ; Decimal
LDAL #'A'           ; Character literal

Comments:

; Single-line comment

Data Directives:

.equ CONSTANT $1234         ; Define constant
.bytes "Hello", 0           ; Byte array
.word $1234, $5678          ; Word array

Hello World:

    LDA @MSG
    LDX #0
    LDY #0
    CALL @WRITE_STRING
    RET

MSG:
    .bytes "HELLO WORLD!", 0

Fill Screen with Stars:

    LDAL #'*'           ; Character to draw
    LDX #0              ; Start column
    LDY #0              ; Start row
    
loop:
    CALL @WRITE_CHAR
    INC X
    CMP X, #40
    JNZ @loop
    
    LDX #0              ; Reset column
    INC Y
    CMP Y, #25
    JNZ @loop
    
    RET

Random Number Generator (Galois LFSR):

.equ RND_SEED $EFF0

rnd_init:
    LDA [$EF05]         ; Hardware clock
    LDB [$EF06]
    XOR A, B
    STA [@RND_SEED]
    RET

rnd_byte:
    LDA [@RND_SEED]
    MOV B, A
    ANDB BL, $01        ; Check LSB
    SHR A               ; Shift right
    CMPB BL, $00
    JZ @no_xor
    LDB $B400           ; Polynomial
    XOR A, B
no_xor:
    STA [@RND_SEED]
    RET

Measured Performance:

• Clock speed: 10 MHz base, up to 100 MHz
• Sustained MIPS: 60 MIPS (i7-12700k)
• Memory bandwidth: ~280 MB/s
• Sound system overhead: < 5% CPU time
• Video refresh: 60 Hz (16.67ms frame time)

Optimization Notes:

• Batch instruction execution (787,401 instructions per batch at 100 MIPS target)
• MessageChannel-based scheduling for low-latency loops
• Time-debt throttling maintains consistent clock rate
• Sound updates triggered by register writes (not polling)

Architecture: WebAssembly-based virtual CPU Languages: AssemblyScript (CPU core), JavaScript (I/O systems) Memory Model: 4 banks of 64k RAM Audio Backend: SD-450 4 voice polyphonic 5 waveform Audio System Video Backend: 9 mode Text and Graphics pixel-perfect render engine

1. print_byte - Display 16-bit number at cursor
2. print_char_at - Single character without moving cursor
3. clear_screen - Fill screen with spaces
4. print_at - Positioned string output
5. string_compare - String equality test
6. string_to_upper - Case conversion
7. wait_key - Blocking key wait
8. random_range - Bounded random numbers
9. draw_box - Border rendering
10. scroll_region - Partial screen scrolling
11. save_screen/restore_screen - Screen buffer management

• Bresenham line drawing (implemented)
• Sprite system with hardware acceleration
• Tilemap support for scrolling backgrounds
• Bitmap font rendering

• PCM streaming for voice/SFX
• Additional waveforms (filtered noise, PWM variants)
• Other sample playback (Opus/Ogg compressed)
• LFO and vibrato effects

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SD-8516 Technical Manual - Revision 1.0 Copyright © 2025 Appledog Hu All specifications subject to change as quantum resonance research continues.