# SerialIO routines#include "regdef.h"#define uart_addr 0xF0000840.previous.text.align 2.globl UART_TXD			.globl UART_TXD_STR		.globl UART_TXD_DECIMAL		.globl UART_TXD_HEX		.globl UART_TXD_HEX_DIGIT	.globl UART_RXD			.globl UART_RXD_HEX		#------------------------------------------------------------------------------# Send the lower 8 bits of a0# Waits until there is room in the tx fifo buffer# Dirties t0, t1.align 2.ent UART_TXDUART_TXD:    # wait until the fifo isn't full    li   t0, uart_addr  UART_TXD.loop:    lw   t1, 4(t0)                    # load the control word    srl  t1, t1,  16    beq  t1, zero, UART_TXD.loop    nop    sw   a0, 0(t0)    jr   ra    nop.end UART_TXD#------------------------------------------------------------------------------# Send a null-terminated string starting at byte address a0# Dirties t0, t1, t2, t3.align 2.ent UART_TXD_STRUART_TXD_STR:    add  t2, zero, ra		# save the return address    add  t3, zero, a0		# save the string address  UART_TXD_STR.start:    lb   a0, 0(t3)    beq  a0, zero, UART_TXD_STR.end    nop    jal  UART_TXD    addi t3, t3, 1    j    UART_TXD_STR.start    nop  UART_TXD_STR.end:    jr   t2    nop.end UART_TXD_STR#------------------------------------------------------------------------------# Transmit the value in a0 as an ascii integer# Dirties t0, t1, t2, t3, t4, t5.align 2.ent UART_TXD_DECIMALUART_TXD_DECIMAL:    add  t3, zero, a0    addi t4, zero, 9    addi t5, zero, 0  UART_TXD_DECIMAL.loop:    addi t2, zero, 1    addi t1, t4, 0    addi t0, zero, 10  UART_TXD_DECIMAL.mul10:    mult t2, t0    mflo t2    addi t1, t1, -1    bne  t1, zero, UART_TXD_DECIMAL.mul10    nop    div  zero, t3, t2    mflo t1    bne  t1, zero, UART_TXD_DECIMAL.send    nop    beq  t5, zero, UART_TXD_DECIMAL.endsend  UART_TXD_DECIMAL.send:    addi a0, t1, 48    addi t5, ra, 0    jal  UART_TXD    nop    addi ra, t5, 0    addi t5, zero, 1    mflo t1    mul  t1, t2    mflo t2    sub  t3, t3, t2  UART_TXD_DECIMAL.endsend:    addi t4, t4, -1    bne t4, zero, UART_TXD_DECIMAL.loop    nop    addi a0, t3, 48    jal UART_TXD    nop    jr  ra    nop.end UART_TXD_DECIMAL#------------------------------------------------------------------------------# Transmit 8 hex digits representing the word in a0# Dirties t0, t1, t2, t3, t4, t5.align 2.ent UART_TXD_HEXUART_TXD_HEX:    add  t2, zero, ra		# save the return address    add  t3, zero, a0		# save the value    addi t4, zero, 32			# shift amount  UART_TXD_HEX.loop:    addi t4, t4, -4    srl a0, t3, t4    andi a0, a0, 15    addi t5, a0, -10    bgez t5, UART_TXD_HEX.letter    nop    addi a0, a0, 48    j    UART_TXD_HEX.tx    nop  UART_TXD_HEX.letter:    addi a0, a0, 55  UART_TXD_HEX.tx:    jal  UART_TXD    nop    bne  t4, zero, UART_TXD_HEX.loop    nop    jr   t2    nop.end UART_TXD_HEX#------------------------------------------------------------------------------# Transmit lower 4 bits of a0 as a hex digit# Dirties t0, t1, t2, t3.align 2.ent UART_TXD_HEX_DIGITUART_TXD_HEX_DIGIT:    add  t2, zero, ra		# save the return address    andi a0, a0, 15    addi t3, a0, -10    bgez t3, UART_TXD_HEX_DIGIT.letter    nop    addi a0, a0, 48    j    UART_TXD_HEX_DIGIT.tx    nop  UART_TXD_HEX_DIGIT.letter:    addi a0, a0, 55  UART_TXD_HEX_DIGIT.tx:    jal UART_TXD    nop    jr   t2    nop.end UART_TXD_HEX_DIGIT#------------------------------------------------------------------------------# Return a byte in v0, and the number of (remaining) bytes# in the receive fifo in v1# Dirties t0, t1.align 2.ent UART_RXDUART_RXD:    # wait until a read is valid      UART_RXD.loop:    li   t0, uart_addr    lw   t1, 0(t0)    andi t0, t1, 0x8000    beq  t0, zero, UART_RXD.loop    nop    andi v0, t1, 0x00FF    srl  v1, t1, 15    jr   ra    nop.end UART_RXD#------------------------------------------------------------------------------# Return a byte in v0 from hex (i.e. 0..9,a..f => 0..15),# and the number of (remaining) bytes in the receive fifo in v1# If a non-hex digit is received, 0 is returned# Dirties t0, t1, t2, t3.align 2.ent UART_RXD_HEXUART_RXD_HEX:    add  t2, zero, ra		# save the return address    jal  UART_RXD    nop    addi t3, v0, -48    bltz  t3, UART_RXD_HEX.err    nop    addi t3, v0, -58    bgez t3, UART_RXD_HEX.notnum    nop    addi v0, v0, -48    jr   t2    nop  UART_RXD_HEX.notnum:    addi t3, v0, -65    bltz  t3, UART_RXD_HEX.err    nop    addi t3, v0, -71    bgez t3, UART_RXD_HEX.notupper    nop        addi v0, v0, -55    jr   t2    nop  UART_RXD_HEX.notupper:    addi t3, v0, -97    bltz  t3, UART_RXD_HEX.err    nop    addi t3, v0, -103    bgez t3, UART_RXD_HEX.err    nop    addi v0, v0, -87    jr   t2    nop  UART_RXD_HEX.err:    add  v0, zero, zero    jr   t2    nop .end UART_RXD_HEX#------------------------------------------------------------------------------