From 8f6eed4e102500204879d848572547b35a267cea Mon Sep 17 00:00:00 2001
From: Jacques Comeaux <jacquesrcomeaux@protonmail.com>
Date: Sat, 23 Dec 2023 14:12:08 -0600
Subject: Use crystal oscilator for system clock

---
 clocks.s | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)
 create mode 100644 clocks.s

(limited to 'clocks.s')

diff --git a/clocks.s b/clocks.s
new file mode 100644
index 0000000..09a0f6d
--- /dev/null
+++ b/clocks.s
@@ -0,0 +1,18 @@
+.syntax unified
+.cpu cortex-m0plus
+.thumb
+
+.equ CLOCKS_BASE, 0x40008000
+.equ CLK_REF_CTRL_OFST, 0x30
+.equ CLK_SYS_CTRL_OFST, 0x3c
+
+.type setup_clocks, %function
+.global setup_clocks
+
+setup_clocks:
+  ldr r1, =CLOCKS_BASE
+  movs r0, 2 // use xosc (=0x2) as clk_ref source
+  str r0, [r1, CLK_REF_CTRL_OFST]
+  movs r0, 1 // use auxsrc (default pll_sys, =0x1) as clk_sys source
+  str r0, [r1, CLK_SYS_CTRL_OFST]
+  mov pc, lr
-- 
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