Instructor Notes

March 3, 2008

Assignment Reminders

• Initial Term Project Proposal: due March 9 midnight (discussion)
• Midterm: March 12 (discussion)
• Hello Noise: March 25th

  • focus on sound effects for the games, not the music i.e. handing in Lemon Player is not going to fly.

Quote

"Engineering problems are under-defined, there are many solutions, good, bad and indifferent. The art is to arrive at a good solution. This is a creative activity, involving imagination, intuition and deliberate choice." -- Ove Arup

Hello GameBoy and Hello Sprite projects

Feedback

• delay routine doesn't look at c
• no value given to bc before calling delay
• hard-coding one character at a time
• more comments in your code
  • put your name on your code!

Examples

Alec's Code:

• 97 - 101 should be a routine or a macro...
• 2nd and 3rd dot are hard-coded...

• call BigLoop. What happens to SP?

• how can the code take input at any time instead of just before printing "loading"?

  • gbspec example: lines 574-608:

      ; **** Main Game Loop ****
      Main:
            halt                    ; stop system clock
                                    ; return from halt when interrupted
            nop                     ; (See WARNING above.)
            ld      a,(VblnkFlag)
            or      a               ; V-Blank interrupt ?
            jr      z,Main          ; No, some other interrupt
            xor     a
            ld      (VblnkFlag),a   ; Clear V-Blank flag
            call    Controls        ; button inputs
            call    Game            ; game operation
            jr      Main
    
      ; **** V-Blank Interrupt Routine ****
      Vblnk:
            push    af
            push    bc
            push    de
            push    hl
            call    SpriteDma       ; Do sprite updates
            ld      a,1
            ld      (VblnkFlag),a
            pop     hl
            pop     de
            pop     bc
            pop     af
            reti
    

Tien's Code:

• delay loops 442-460
• do a variable to demonstrate?

Look at some Hello Sprite projects

• Daniel Schossow?
  • understanding the never-ending loop --- purpose etc.
• Tommy
  • music concurrently with whatever is happening in your game etc.

Z80 wrapup-part I

• addressing modes (page 44 of Z80 user's manual)
  • Immediate: opcode and 1 byte
  • Immediate extended: opcode and 2 byte data
  • Modified Page 0 Addressing: (b5 b4 b3 0 0 0)
  • Relative Addressing
  • Extended Addressing: and 2 byte address

  • Indexed Addressing: not used on GameBoy. on Z80 offers displacement to IX or IY

  • Register Addressing:
  • Implied Addressing: register is implied
  • Register Indirect Addressing: pointer to location in memory
  • Bit Addressing

• how does the assembler assemble? From http://www.nersc.gov/vendor_docs/ibm/asm/assembler_passes.htm

  • First Pass
    • Checks to see if the instructions are legal in the current assembly mode.
    • Allocates space for instructions and storage areas you request.
    • Fills in the values of constants, where possible.
    • Builds a symbol table, also called a cross-reference table, and makes an entry in this table for every symbol it encounters in the label field of a statement.
  • Second Pass
    • Examines the operands for symbolic references to storage locations and resolves these symbolic references using information in the symbol table.
    • Ensures that no instructions contain an invalid instruction form.
    • Translates source statements into machine code and constants, thus filling the allocated space with object code.
    • Produces a file containing error messages, if any have occurred.
• timing (T cycles, M cycles) (Z80 manual page 80)
  • 1 T cycle is 1/f of clock
  • each machines cycle is one of
    • 1st is always "fetch" which is 4-6 T cycles long
    • subsequent M cycles move data to or from memory
  • see page 12 of z80 manual
• instruction types (see Z80 manual page vi)
  • 8 bit load group
  • 16 bit load group
  • exchange, block transfer, and search group
  • 8 bit arithmetic group
    • DAA
    • note addressing mode
  • general-purpose arithmetic and CPU control
  • 16 bit arithmetic group
  • rotate and shift group
  • bit set, reset, and test group
  • jump group
  • call and return group
  • input and output group

• differences between Z80 and GameBoy

  • gbspec lines 60-90:

     The following are added instructions:
    
      ADD  SP,nn             ;nn = signed byte
      LD  (HLI),A            ;Write A to (HL) and increment HL
      LD  (HLD),A            ;Write A to (HL) and decrement HL
      LD  A,(HLI)            ;Write (HL) to A and increment HL
      LD  A,(HLD)            ;Write (HL) to A and decrement HL
      LD  A,($FF00+nn)
      LD  A,($FF00+C)
      LD  ($FF00+nn),A
      LD  ($FF00+C),A
      LD  (nnnn),SP
      LD  HL,SP+nn           ;nn = signed byte
      STOP                   ;Stop processor & screen until button press
      SWAP r                 ;Swap high & low nibbles of r
    
     The following instructions have been removed:
    
      Any command that uses the IX or IY registers.
      All IN/OUT instructions.
      All exchange instructions.
      All commands prefixed by ED (except remapped RETI).
      All conditional jumps/calls/rets on parity/overflow and sign flag.
    
     The following instructions have different opcodes:
    
      LD  A,[nnnn]
      LD  [nnnn],A
      RETI