; Tool for controlling tf_hh's SRAM upgrade (512K v4.5, or 576K v2 for 600XL).

; Gets built with various defines, see README.txt. Non-coldstart
; builds can be prepended to another .xex file to set the upgrade's
; mode automatically when that .xex is loaded.

; Reverse-engineered by disassembling setmem.xex.

; Note that the upgrade's mode can *only* be changed while the
; Start key is held down, so this can't be 100% non-interactive.

 .include "atari.inc"
 .include "xex.inc"

 .include "ver.s"

 .ifndef magic_value
  .error "You must define magic_value to 0, 1, or 2."
 .endif

 .define rambo_msg   "for 512K/RAMBO mode"
 .define compy_msg   "for 256K/Compy mode"
 .define disable_msg "to disable memory upgrade"

 .if magic_value = 0
   .ifdef reverse_logic
    .define mode_msg compy_msg
    .define xex_name "U256R"
   .else
    .define mode_msg rambo_msg
    .define xex_name "U512"
   .endif
 .else
  .if magic_value = 1
   .define mode_msg disable_msg
   .define xex_name "UOFF"
  .else
   .if magic_value = 2
    .ifdef reverse_logic
     .define mode_msg rambo_msg
     .define xex_name "U512R"
    .else
     .define mode_msg compy_msg
     .define xex_name "U256"
    .endif
	.else
    .error .sprintf("Invalid magic_value (must be 0, 1, or 2, not %d)", magic_value)
   .endif
  .endif
 .endif

 .out .sprintf("Using magic_value %d, message '%s'", magic_value, mode_msg)

 loadaddr = $8000

 magic_register = $d3f3

 xex_org loadaddr

 ; runaddr is fake (just an RTS), put here so the tool can be run
 ; standalone under "smart" DOSes like SDX that want to jump to the
 ; load address.
runaddr: rts

magic_bits: .byte magic_value

prompt_msg:
 .byte xex_name
 .ifdef coldstart
  .byte "X"
 .endif
 .byte " v", VERSION, " by Urchlay", $9b, $9b, "Press Start ", mode_msg
 .ifdef coldstart
  .byte $9b, "The Atari will reboot!", $9b
  .byte "Press any other key to abort.", $9b
 .endif
 .byte 0

;;; subroutines

printchr:   ; print character in A register.
 tay        ; save A (character to print).
 lda ICPTH  ; set up stack, so it looks like a JSR to the
 pha        ;   put-one-byte address for E:,
 lda ICPTL  ;   which the OS has conveniently stashed
 pha        ;   in IOCB #0.
 tya        ; restore A (put-one-byte argument).
 rts        ; "return" to put-one-byte, which will return to printchr's caller.

printmsg:   ; print message pointed to by A/X
 sta FR0
 stx FR0+1
 lda #0
 sta FR0+2
pmloop:
 ldy FR0+2
 lda (FR0),y
 beq pmdone
 jsr printchr
 inc FR0+2
 bne pmloop
pmdone:
 rts

; wait for CONSOL to equal A
waitconsol:
 cmp CONSOL
 bne waitconsol
 ; a bit of debouncing...
 sta WSYNC
 sta WSYNC
 sta WSYNC
 sta WSYNC
 cmp CONSOL
 bne waitconsol
 rts

;;; main program

entrypoint:
 ; print our prompt
 lda #<prompt_msg
 ldx #>prompt_msg
 jsr printmsg

.if 0
 ; no idea why setmem.xex clicks the console speaker...
 lda #8
 sta CONSOL
.endif

 ; just in case: make sure Start's not being held down.
 lda #7
 jsr waitconsol

 ; save previous contents of PBCTL and PORTB. diddling $d3f3
 ; affects PBCTL whether Start is held down or not... and
 ; changing PBCTL crashes SpartaDOS X.
 ldx PBCTL
 ldy PORTB

 ; wait for the user to press Start. can't skip this, the magic
 ; register can only be updated when Start is pressed.
.ifdef coldstart
 ; if the user presses any regular key, exit the program without
 ; changing modes or rebooting.
 lda #$ff
 sta CH
waitkey:
 lda CH
 cmp #$ff
 beq wk_chkstart
 lda #$ff
 sta CH
 rts
wk_chkstart:
 lda CONSOL
 cmp #6
 bne waitkey
.else
 lda #6
 jsr waitconsol
.endif

 ; disable both IRQ and NMI interrupts.
 sei
 lda #0
 sta NMIEN

 ; update the magic, the same way setmem.xex does.
 lda magic_register
 and #$fc
 ora magic_bits
 sta magic_register

 ; original code waits for the user to release the Start key before
 ; re-enabling interrupts. I don't think this matters, but I'll do it.
 lda #7
 jsr waitconsol

 ; restore previous PIA contents.
 stx PBCTL
 sty PORTB

 ; re-enable interrupts and exit.
 lda #$40
 sta NMIEN
 cli

.ifdef coldstart
 jmp COLDSV
.else
 rts
.endif

 xex_run runaddr

 ; the real work gets done by an init routine.
 xex_init entrypoint