os-core/kernel/arm64/uart.s

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2019-02-23 21:22:20 +01:00
# file : uart.s
# project : Löwe OS
# authors : Elias Löwe <elias@lowenware.com>
# address of UART for virt device in qemu
# -----------------------------------------------------------------------------
.global _uart_putc # print single character uart
.global _uart_putx # print integer in HEX format to uart
.global _uart_puts # print null-terminated string to uart
# -----------------------------------------------------------------------------
.text
# helper to avoid extra data moving
# @x1 character print
uart_putc:
STP x2, lr, [sp, -16]!
MOV x2, 0x09000000 # set UART address
STRB w1, [x2] # put character out
LDP x2, lr, [sp], 16
RET
# -----------------------------------------------------------------------------
# print character to uart
# @x0 character print
_uart_putc:
STR lr, [sp, -16]!
MOV x1, x0 # set arguments
BL uart_putc # put character out
LDR lr, [sp], 16
RET
# -----------------------------------------------------------------------------
# @x0 integer to print
_uart_putx:
STP lr, x3, [sp, -32]!
STP x0, x1, [sp, 16]
LDR x3, =60 # init bits counter 64-4
1:
LSR x1, x0, x3 # shift to digit
AND x1, x1, 0xF # keep only digit
CMP x1, 9 # compare it to 9
BLS 2f # less or equal
ADD x1, x1, 0x37 # turn into ASCII HEX char
B 3f # continue to output
2:
ADD x1, x1, 0x30 # turn into ASCII num char
3:
BL uart_putc # output carachter
CBZ x3, 0f # if counter == 0 return
SUB x3, x3, 4 # otherwise subtract counter by 4
B 1b # repeat
0:
LDP lr, x3, [sp], 16
LDP x0, x1, [sp], 16
RET
# -----------------------------------------------------------------------------
# @x0 pointer to string
_uart_puts:
STR lr, [sp, -16]!
STP x0, x1, [sp, -16]!
1:
LDRB w1, [x0], 1 # load byte of string from address in x0
CBZ w1, 0f # return if zero
BL uart_putc # put charcter out
B 1b # loop
0:
LDP x0, x1, [sp], 16
LDR lr, [sp], 16
RET
# -----------------------------------------------------------------------------