basic physical memory page allocator

Signed-off-by: Matthew Wozniak <me@woz.blue>

1 files changed, 42 insertions, 0 deletions

diff --git a/src/asm/boot.S b/src/asm/boot.S
new file mode 100644
index 0000000..bd50b4c
--- /dev/null
+++ b/src/asm/boot.S
@@ -0,0 +1,42 @@
+# bootloader for my kernel
+.option norvc
+.section .data
+.section .text.init
+.global _start
+_start:
+	# any harts not bootstrapping need to wait for an IPI
+	csrr t0, mhartid
+	bnez t0, 3f
+	# satp should be zero, but make sure
+	csrw satp, zero
+.option push
+.option norelax
+	la gp, __global_pointer$
+.option pop
+	# clear bss
+	la a0, _bss_start
+	la a1, _bss_end
+	bgeu a0, a1, 2f
+1:
+	sd zero, (a0)
+	addi a0, a0, 8
+	bltu a0, a1, 1b
+2:
+	# set up stack
+	la sp, _stack_end
+	# set kmain to the return address and then return
+	li t0, (0b11 << 11) | (1 << 7) | (1 << 3)
+	la t1, kmain
+	la t2, asm_trap_vector
+	li t3, 0 # (1 << 3) | (1 << 7) | (1 << 11)
+	csrw mstatus, t0
+	csrw mepc, t1
+	csrw mtvec, t2
+	csrw mie, t3
+	mret
+
+
+# wait for interrupt
+3:
+	wfi
+	j 3b