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;==============================================================================

; Test code for the A-Z80 CPU that prints "Hello, World!"

; Also used to test responses to interrupts.

;==============================================================================

    org 0

start:

    jmp boot

    ; BDOS entry point for various functions

    ; We implement subfunctions:

    ;  C=2  Print a character given in E

    ;  C=9  Print a string pointed to by DE; string ends with '$'

    org 5

    ld  a,c

    cp  a,2

    jz  bdos_ascii

    cp  a,9

    jz  bdos_msg

    ret

bdos_ascii:

    ld  bc,10*256   ; Port to check for busy

    in  a,(c)       ; Poll until the port is not busy

    bit 0,a

    jnz bdos_ascii

    ld  bc,8*256    ; Port to write a character out

    out (c),e

    ret

bdos_msg:

    push de

    pop hl

lp0:

    ld  e,(hl)

    ld  a,e

    cp  a,'$'

    ret z

    call bdos_ascii

    inc hl

    jmp lp0

;---------------------------------------------------------------------

; RST38 (also INT M0)  handler

;---------------------------------------------------------------------

    org 038h

    push de

    ld  de,int_msg

int_common:

    push af

    push bc

    push hl

    ld  c,9

    call 5

    pop hl

    pop bc

    pop af

    pop de

    ei

    reti

int_msg:

    db  "_INT_",'$'

;---------------------------------------------------------------------

; NMI handler

;---------------------------------------------------------------------

    org 066h

    push af

    push bc

    push de

    push hl

    ld  de,nmi_msg

    ld  c,9

    call 5

    pop hl

    pop de

    pop bc

    pop af

    retn

nmi_msg:

    db  "_NMI_",'$'

;---------------------------------------------------------------------

; IM2 vector address and the handler (to push 0x80 by the IORQ)

;---------------------------------------------------------------------

    org 080h

    dw  im2_handler

im2_handler:

    push de

    ld  de,int_im2_msg

    jmp int_common

int_im2_msg:

    db  "_IM2_",'$'

boot:

    ; Set the stack pointer

    ld  sp, 16384    ; 16 Kb of RAM

    ; Set up for interrupt testing: see Z80\cpu\toplevel\test_top.sv

    ; IMPORTANT: To test IM0, Verilog test code needs to put 0xFF on the bus

    ;            To test IM2, the test code needs to put a vector of 0x80 !!

    ;            This is done in tb_iorq.sv

    im  2

    ld  a,0

    ld  i,a

    ei

    ;halt

    ; Jump into the executable at 100h

    jmp 100h

;==============================================================================

;

; Prints "Hello, World!"

;

;==============================================================================

    org 100h

    ld  hl,0

    ld  (counter),hl

exec:

    ld  de,hello

    ld  c,9

    call 5

    ; Print the counter and the stack pointer to make sure it does not change

    ld  hl, (counter)

    inc hl

    ld  (counter),hl

    ld  hl, text

    ld  a,(counter+1)

    call tohex

    ld  hl, text+2

    ld  a,(counter)

    call tohex

    ld  (stack),sp

; Several options on which values we want to dump, uncomment only one:

    ld  hl, text+5

;   ld  a,(stack+1)     ; Dump stack pointer (useful to check SP)

    ld  a, i            ; Show IR register

    call tohex

    ld  hl, text+7

;   ld  a,(stack)       ; Dump stack pointer (useful to check SP)

    ld  a, r            ; Show IR register

    call tohex

; Two versions of the code: either keep printing the text indefinitely (which

; can be used for interrupt testing), or print it only once and die

die:

    jr exec

;    jr die

tohex:

    ; HL = Address to store a hex value

    ; A  = Hex value 00-FF

    push af

    and  a,0fh

    cmp  a,10

    jc   skip1

    add  a, 'A'-'9'-1

skip1:

    add  a, '0'

    inc  hl

    ld   (hl),a

    dec  hl

    pop  af

    rra

    rra

    rra

    rra

    and  a,0fh

    cmp  a,10

    jc   skip2

    add  a, 'A'-'9'-1

skip2:

    add  a, '0'

    ld   (hl),a

    ret

; Print a counter before Hello, World so we can see if the

; processor rebooted during one of the interrupts. Also, print the content

; of the SP register which should stay fixed and "uninterrupted"

counter: dw 0

stack: dw 0

hello:

    db  13,10

text:

    db '---- ---- Hello, World!$'

end