Start implementing irq setup and handling

1 files changed, 34 insertions, 0 deletions

diff --git a/software/first/setup_timer_irq.S b/software/first/setup_timer_irq.S
new file mode 100644
index 0000000..4ae714f
--- /dev/null
+++ b/software/first/setup_timer_irq.S
@@ -0,0 +1,34 @@
+.section .text
+.align 2
+.global setup_timer_irq
+.include "memory_map.inc"
+
+setup_timer_irq:
+	addi sp, sp, -16 # Allocate stack frame
+	sw ra, 12(sp)    # save return address to the stack
+
+	lw t0, irq_handler  # load address of irq_handler 
+	slli t0, t0, 1      # shift address left by one; LSB will be 0 which is direct mode (what we want)
+	csrw mtvec, t0      # write handler address and mode
+
+  # Here we cannot use csrsi because it can only set up to 5 bits
+	li t0, 0x80     # set 7th bit (indexed from 0)
+	csrw mie, t0    # activate machine timer interrupt
+
+	# write high value to the timercmp just to be sure we don't
+	# trigger an interrupt by mistake
+	li t0, 0x7FFFFFFF  # high number
+	li t1, 0xFFFFFFFF  # high number
+	li t2, MTIMECMP    # load address of timecmp register
+	sw t0, 4(t2)       # store the first number to the upper part first
+	sw t1, 0(t2)       # then the second to the lower part
+
+	csrsi mstatus, 0x4  # set 3rd bit to activate machine interrupts.
+
+	lw ra, 12(sp)   # load return address
+	addi sp, sp, 16 # deallocate stack frame
+	ret
+
+
+irq_handler:
+	mret