Tupto's Little Ape Computer

Made for Essex CSEE Society Summer Challenge. Very unpolished, may come back to this project at some point and fix some things, especially with regard to the GUI.

Memory Map

0000-0EFF   BIOS
0F00-0FFF   Interrupt Control
1000-BFFF   RAM
C000-FFFF   VRAM

Control

Map

0F00    IME    Interrupt master enable      (0=off, 1=on)
0F01    IRQ    Interrupt request mode       (0=off, 1=on)
0F02    IE     Interrupt enable             (bit flags)
0F03    IF     Interrupt request flags      (bit flags)
0F10    IH     Interrupt handler            (function pointer)
0F20    VM     Video mode                   (0=indexed, 1=direct)

0F00 - IME - Interrupt master enable

Bit     Desc
0       Enable/ disable interrupts          (0 = disable all, 1 = check IE)
1-15    Not used

0F01 - IE - Interrupt master enable

Bit     Desc
0       VBlank      (0 = disable, 1 = enable)
1       HBlank      (0 = disable, 1 = enable)
2       Keypad      (0 = disable, 1 = enable)
3-15    Not used

0F02 - IF - Interrupt request flags

Bit     Desc
0       VBlank      (0 = disable, 1 = enable)
1       HBlank      (0 = disable, 1 = enable)
2       Keypad      (0 = disable, 1 = enable)
3-15    Not used

Registers

• A
  • General purpose
• B
  • General purpose
• C
  • General purpose
• D
  • General purpose
• E
  • General purpose (cannot use immediate byte mode)
• Stack Pointer
  • Points to current stack location
• Program Counter
  • Points to program instruction
• Flags
  • Sign (is negative)
  • Zero (is zero)
  • Carry (if last operation resulted in a carry)

Opcodes

HLT     0       halt
ADD     1       add
SUB     2       subtract
AND     3       logical AND
OR      4       logical OR
XOR     5       logical XOR
LSL     6       logical shift left
LSR     7       logical shift right
MOV     8       move value to register
LDR     9       load register
STR     a       store register
B       b       branch
    BS      b1      branch if sign bit
    BZ      b2      branch if zero bit
    BC      b3      branch if carry bit
BL       c      branch with link
    BLS     c1      branch with link if sign bit
    BLZ     c2      branch with link if zero bit
    BLC     c3      branch with link if carry bit
PUSH    d       push to stack
POP     e       pop from stack
RET     f       return to linked address

HLT

Halts execution of the program by attempting to divide by 0

ADD, SUB, AND, OR, XOR, LSL, LSR

Mathmatical/ bitwise operations.

MOV

Move a value into a target register. Value can be indirect, immediate byte, or immediate word value

LDR, STR

Load/ store a value from/ to the bus.

B, BS, BZ, BC

Branch opertations. If condition is met PC will be set to the given value.

BL, BLS, BLZ, BLC

Branch with link opertations. If condition is met PC will be pushed to the stack and then PC will be set to the given value.

PUSH, POP

Push/ pop a value to the stack.

RET

Pop a linked address from the stack into PC.

Opcode Formats

Note: Jump opcodes do not use a target register and its value is ignored

Indirect

|   15  14  13  12  11  10  9   8   7   6   5   4   3   2   1   0
+------------------------------------------------------------------
|   [   opcode   ]  0   X   X   X   X   [ reg T ]   X   [ reg S ]

Immediate byte

Only registers A-D can be target registers for immediate byte values. Immediate bytes are treated as signed PC relative values for jumps.

|   15  14  13  12  11  10  9   8   7   6   5   4   3   2   1   0
+------------------------------------------------------------------
|   [   opcode   ]  1   0   [reg T] [       immediate value       ]

Immediate word

|   15  14  13  12  11  10  9   8   7   6   5   4   3   2   1   0   |   15  14  13  12  11  10  9   8   7   6   5   4   3   2   1   0  
+-------------------------------------------------------------------+------------------------------------------------------------------
|   [   opcode   ]  1   1   X   X   X   X   X   X   X   [ reg T ]   |   [                      immediate value                        ]

Implict

HLT, RET

|   15  14  13  12  11  10  9   8   7   6   5   4   3   2   1   0
+--------------------------------------------------------------------
|   [   opcode   ]  0   0   0   0   X   X   X   X   X   X   X   X

PUSH, POP

|   15  14  13  12  11  10  9   8   7   6   5   4   3   2   1   0
+--------------------------------------------------------------------
|   [   opcode   ]  X   X   X   X   X   PC  SP  E   D   C   B   A

BIOS

00      Soft reset
02      Interrupt vector
04      Sine
06      Cosine
08      ArcTan
0A      ArcTan2