JSVM

16 bit js virtual machine implementation

Memory model

Virtual CPU use:

• RAM memory (memory size can be changed). Flat model, 0x0000 - 0xFFFF (Up to 64Kb).
• Internal registers memory (access only via registers).

Flash memory now not used.

Register set

Actual information can be found here.

• IP - Instruction pointer. Register value contains memory address of next command for executing.
• AC - Accumulator.
• SP - Stack pointer. Register value contains memory address of stack head.
• Rx - some of general purpose registers.

Program execution

After CPU start IP register contain 0x0000 address, fetch instruction from RAM and start executing.

Stack

After CPU start SP register contain RAM memory size - 2 address. After push some data SP value decreased by 2 bytes and after pop - increased by 2 bytes.

Instruction set

Actual information can be found here.

| Opcode | Command | Arguments | Sample | Description | | ------ | ------- | ------------ | ------------- | ----------------------------------- | | 0x00 | NOP | | | No operation | | 0x?? | PUSH | 0x???? | PUSH 0x1234 | Push 16 bit constant to stack | | 0x?? | PUSH | Rx | PUSH R4 | Push register value to stack | | 0x?? | POP | Rx | POP R1 | Pop value from stack to register | | 0xFF | HLT | | | Halt |