uart.asm
nihirash_uGoph/uart.asm
UART_DATA_REG = #c6
UART_STAT_REG = #c7
UART_BYTE_RECIVED = #80
UART_BYTE_SENDING = #40

; Enable UART
; Cleaning all flags by reading UART regs
; Wastes AF and BC
uartBegin:
    ld bc, ZXUNO_ADDR
    ld a, UART_STAT_REG
    out (c), a

    ld bc, ZXUNO_REG
    in A, (c)
    
    ld bc, ZXUNO_ADDR
    ld a, UART_DATA_REG
    out (c), a
    
    ld bc, ZXUNO_REG
    in A, (c)
    ret

; Pushes to UART zero-terminated string
; HL - string poiner
uartWriteStringZ:
    ld a, (hl)
    and a
    ret z
    push hl
    call uartWriteByte
    pop hl
    inc hl
    jp uartWriteStringZ

; Blocking read one byte
uartReadBlocking:
    call uartRead
    push af
    ld a, 1
    cp b
    jr z, urb 
    pop af
    ret nz
    jp uartReadBlocking
urb: 
    pop af
    ret

; Write single byte to UART
; A - byte to write
; BC will be wasted
uartWriteByte:
    push af
    ld bc, ZXUNO_ADDR
    ld a, UART_STAT_REG
    out (c), a

waitWriteReady:
    ld bc, ZXUNO_REG 
    in A, (c)
    and UART_BYTE_RECIVED
    jr nz,  is_recvF
checkSent:
    ld bc, ZXUNO_REG 
    in A, (c)
    and UART_BYTE_SENDING
    jr nz, checkSent

    ld bc, ZXUNO_ADDR
    ld a, UART_DATA_REG
    out (c), a
    ld bc, ZXUNO_REG
    pop af
    out (c), a
    ret
is_recvF:
    push af
    push hl
    ld hl, is_recv
    ld a, 1
    ld (hl), a
    pop hl
    pop af
    jr checkSent

; Is data avail in UART
; NZ - Data Presents
; Z - Data absent
uartAvail:
    ld a, (is_recv)
    and 1
    ret nz

    ld a, (poked_byte)
    and 1
    ret nz

    call uartRead

    push af
    ld a, b
    and 1
    jr z, noneData
    pop af 
    push af
    ld hl, byte_buff
    ld (hl), a
    ld hl, poked_byte 
    ld a, 1
    ld (hl), a
    pop af
    ld b, a
    ld a, 1
    or a
    ld a, b
    ret
noneData:
    pop bc
    xor a
    ret

; Read byte from UART
; A: byte
; B:
;     1 - Was read
;     0 - Nothing to read
uartRead:
    ld a, (poked_byte)
    and 1
    jr nz, retBuff

    ld a, (is_recv)
    and 1
    jr nz, recvRet

    ld bc, ZXUNO_ADDR
    ld a, UART_STAT_REG
    out (c), a
    
    ld bc, ZXUNO_REG 
    in a, (c)
    and UART_BYTE_RECIVED
    jr nz, retReadByte

    ld b, 0
    ret

retReadByte:
    ld a, 0
    ld (poked_byte), a
    ld (is_recv), a

    ld bc, ZXUNO_ADDR
    ld a, UART_DATA_REG
    out (c), a

    ld bc, ZXUNO_REG
    in a, (c)

    ld b, 1
    ret

recvRet:
    ld bc, ZXUNO_ADDR
    ld a,  UART_DATA_REG
    out (c),a

    ld bc, ZXUNO_REG
    in a, (c)

    ld hl, is_recv
    ld (hl), 0
    
    ld hl, poked_byte
    ld (hl), 0
    
    ld b, 1
    ret

retBuff
    ld a, 0
    ld (poked_byte), a

    ld a, (byte_buff)
    ld b, 1
    ret

poked_byte defb 0
byte_buff defb 0
is_recv defb 0