Each program gets 4 memory regions:
- Code (instructions)
- Operand stack
- Call stack
- "Memory" pages
The first page is used to control the CPU
- 0x00: Page table base
- 0x08: Page table length
- 0x10: Function table base
- 0x18: Function table length
- 0x20: Call stack top
- Only allows 32 nested calls
- 0x40: Pointer to first instruction (right now, 0x50)
- 0x50: Code (until 0x500)
MMU has 1 entry, page 0 points to physical address 0
- PT: 0x500 (until 0x600)
- FT: 0x600 (until 0x700)
- OP stack: 0x700 (until 0x1000)
- Memory: 0x1000-0xFFFF
A page table is defined as a packed list of offsets for physical addresses; the indices into the table are the page number.
The index lookup is done by shifting the address 16 bits to the right:
- 0x00000-0x10000 => Page 1
- 0x10000-0x20000 => Page 2
- ...
An example mapping with two entries:
[0x0, 0x20000]
- Virtual addresses 0x00000-0x0FFFF are identity-mapped into the same physical addresses
- Virtual addresses 0x10000-0x20000 are mapped into the physical address
0x20000-0x30000
List of function-table-entry, index into table = function index
Packed:
- Union [Virtual Address = 32 bits, service_call_id = 32 bits]
- Arg count = 6 bits
- Is import = 1 bit
a call instruction needs some metadata:
- Argument count
- Physical memory address for instruction
Need to save current registers (variable #) Need to pop $ARGC from the stack into registers (variable #)
=> 32 registers