1 files changed, 31 insertions, 0 deletions
diff --git a/setup/clocks.s b/setup/clocks.s
new file mode 100644
index 0000000..83bc9ff
--- /dev/null
+++ b/setup/clocks.s
@@ -0,0 +1,31 @@
+.syntax unified
+.cpu cortex-m0plus
+.thumb
+
+.equ CLOCKS_BASE, 0x40008000
+.equ CLK_REF_CTRL_OFST,  0x30
+.equ CLK_SYS_CTRL_OFST,  0x3c
+.equ CLK_PERI_CTRL_OFST, 0x48
+
+.type setup_clocks, %function
+.global setup_clocks
+
+setup_clocks:
+
+  ldr r1, =CLOCKS_BASE
+
+  // Reference clock
+  movs r0, 0x2 // src = xosc
+  str r0, [r1, CLK_REF_CTRL_OFST]
+
+  // System clock
+  movs r0, 0x0 // src = clk_ref
+  str r0, [r1, CLK_SYS_CTRL_OFST]
+
+  // Peripheral clock
+  movs r0, 1 // set enable
+  lsls r0, 11
+  adds r0, 0x4 << 5 // src = xosc
+  str r0, [r1, CLK_PERI_CTRL_OFST]
+
+  bx lr