From aa72093ffe1abafd605b5ec3b2d50c20b11c14a9 Mon Sep 17 00:00:00 2001
From: Silvan Jegen <s.jegen@gmail.com>
Date: Thu, 1 Aug 2019 18:41:21 +0200
Subject: Start implementing irq setup and handling

---
 software/first/first.c           |  1 +
 software/first/memory_map.inc    |  1 +
 software/first/setup_timer_irq.S | 34 ++++++++++++++++++++++++++++++++++
 software/first/super_blink.h     |  1 +
 4 files changed, 37 insertions(+)
 create mode 100644 software/first/setup_timer_irq.S

(limited to 'software/first')

diff --git a/software/first/first.c b/software/first/first.c
index ede96db..7505d6c 100644
--- a/software/first/first.c
+++ b/software/first/first.c
@@ -14,6 +14,7 @@ int main() {
 		};
 
 		setup_GPIO();
+		setup_timer_irq();
 
 		while (!error) {
 			set_LED(colours[ledNum], ON);
diff --git a/software/first/memory_map.inc b/software/first/memory_map.inc
index e28af43..b532fee 100644
--- a/software/first/memory_map.inc
+++ b/software/first/memory_map.inc
@@ -1,3 +1,4 @@
 .equ GPIO_CTRL_ADDR,  0x10012000
 .equ MTIME,           0x0200BFF8
+.equ MTIMECMP,       0x02004000
 .equ MTIME_FREQUENCY, 33
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
diff --git a/software/first/super_blink.h b/software/first/super_blink.h
index 74cc00a..b53d55d 100644
--- a/software/first/super_blink.h
+++ b/software/first/super_blink.h
@@ -9,4 +9,5 @@
 
 void setup_GPIO();
 int set_LED(int color, int state);
+void setup_timer_irq();
 void delay(int milliseconds);
-- 
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