Initiated

.gitignore

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+.elf
+.o
+build/

AUTHORS

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+Elias Löwe <elias@lowenware.com>

LICENSE

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+# Lion's Share License -> LSL
+# Löwenware Software Distribution -> LSD

README.md

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+# Löwe OS
+Operating System for ARMv8 (aarch64) architecture.
+

kernel/arm64/Makefile

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+ASM=clang
+TARGET=aarch64-none-elf
+CPU=cortex-a57
+LD=ld.lld
+OBJCOPY=objcopy --target elf64-littleaarch64
+
+all: build/core.bin build/core.elf
+
+# compilation -----------------------------------------------------------------
+
+build/core.o: core/core.s
+	$(ASM) -c -triple --target=$(TARGET) -mcpu=$(CPU) -O0  -g $< -o $@
+
+build/uart.o: core/uart.s
+	$(ASM) -c --target=$(TARGET) -mcpu=$(CPU) -O0  -g $< -o $@
+
+# ELF -------------------------------------------------------------------------
+
+build/core.elf: build/core.o build/uart.o
+	$(LD) -Tcore/core.ld $^ -o $@
+
+# BIN -------------------------------------------------------------------------
+
+build/core.bin: build/core.elf
+	$(OBJCOPY) -O binary $< $@
+
+build/core.sym: build/core.elf
+	$(OBJCOPY) --only-keep-debug $< $@
+	$(OBJCOPY) --strip-debug build/core.elf
+
+# Clean -----------------------------------------------------------------------
+
+clean:
+		rm -f build/*

kernel/arm64/core.ld

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+ENTRY(_core_init)
+
+SECTIONS
+{
+  . = 0x40000000;
+  .text : { *(.text) }
+  .data : { *(.text) }
+  .bss : { *(.bss COMMON) }
+  . = ALIGN(10);
+  . = . + 0x1000;
+  stack_ptr = . ;
+}

kernel/arm64/core.s

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+# file:    core.s
+# project: Löwe OS
+# authors: Elias Löwe <elias@lowenware.com>
+
+# -----------------------------------------------------------------------------
+
+  .global _core_init
+  .extern _uart_puts
+
+# -----------------------------------------------------------------------------
+
+  .text
+
+_core_init:
+  # set up stack pointer using x30 register
+  LDR     x30, =0x40001000
+  MOV     sp,  x30
+  bl      1f
+
+1:
+  LDR     x0,  =some_int
+  BL      _uart_putx
+  LDR     x0,  =greeting
+  BL      _uart_puts
+2:
+  B       2b
+
+# -----------------------------------------------------------------------------
+
+  .data
+
+greeting:
+  .asciz "\nStarting Lowe OS\n"
+
+
+  .equ some_int, 0x1234567890ABCDEF
+
+# -----------------------------------------------------------------------------

kernel/arm64/uart.s

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+# 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
+
+# -----------------------------------------------------------------------------