46 lines
1.3 KiB
ArmAsm
46 lines
1.3 KiB
ArmAsm
; CHIBI PC-09 Prototype #1 Boot ROM -- Serial Driver
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; Copyright (c) 2024-2025 Amber Zeller, Gale Faraday
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; Licensed under MIT
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INCLUDE "hardware.inc"
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;
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;; Serial UART Driver
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;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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SECTION SERIAL
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EXPORT OUTCHAR
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EXPORT OUTSTR
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; Writes a char to the UART in non FIFO mode, preserves A.
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; @param b: char to write
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OUTCHAR
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pshs a ; Preserve A
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NOTREADY@
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lda UART_LSR ; if LSR.THRE == 1 then write
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anda UARTF_LSR_THRE
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bne NOTREADY@ ; Loop if UART not ready yet
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stb UART_BUFR ; Write char
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puls a ; Restore A
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rts
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; Writes a null terminated string to the UART in non FIFO mode, clobbers A and
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; B.
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; @param x: null terminated string start address.
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OUTSTR
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ldb 0,x ; Get the next value from X
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cmpb #$00 ; Make sure that we aren't at a terminator
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beq END@
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leax 1,x ; Increment X for our next char
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NOTREADY@ ; Loop point for UART waiting
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lda UART_LSR ; Wait for UART to be ready
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anda UARTF_LSR_THRE
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bne NOTREADY@
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stb UART_BUFR ; Actually do our write
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bra OUTSTR ; Reset for the next char
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END@ ; Jump point for end of routine
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rts
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