From 6d10f951d5c5ebae58f7c24df1066a479b68d5fa Mon Sep 17 00:00:00 2001
From: Victor Mignot <victor@vmignot.fr>
Date: Thu, 24 Jul 2025 13:54:25 +0200
Subject: nrf52832: add clock driver

---
 src/boot.s  |  8 +++++++
 src/clock.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/clock.h | 10 ++++++++
 src/main.c  |  4 ++++
 4 files changed, 101 insertions(+)
 create mode 100644 src/clock.c
 create mode 100644 src/clock.h

diff --git a/src/boot.s b/src/boot.s
index 626420c..a2bb4b2 100644
--- a/src/boot.s
+++ b/src/boot.s
@@ -3,6 +3,10 @@
 
 .section .vector_table, "a"
 .word __stack_top /* Initial stack pointer */
+
+/**
+ * Exceptions
+ */
 .word _start /* Reset Handler */
 .word _hang  /* Non Maskable Interrupts */
 .word _hang /* Hard Fault */
@@ -15,6 +19,10 @@
 .word _hang /* PendSV */
 .word _hang /* SysTick */
 
+/**
+ * IRQs
+ */
+
 
 .text
 .align
diff --git a/src/clock.c b/src/clock.c
new file mode 100644
index 0000000..5603693
--- /dev/null
+++ b/src/clock.c
@@ -0,0 +1,79 @@
+#include "clock.h"
+#include "types.h"
+#include "peripherals.h"
+
+#define WRITE_CLK_REG(reg, value) (WRITE_REGISTER(CLOCK, reg, value))
+#define READ_CLK_REG(reg) (READ_REGISTER(CLOCK, reg))
+
+enum hfclk_src {
+	HFINT = 0,
+	HFXO = 1,
+};
+
+enum lfclk_src {
+	LFRC = 0,
+	LFXO = 1,
+	LFSYNT = 2,
+};
+
+/**
+ * Memory-mapped registers for the CLOCK peripheral with their offset from its base address,
+ * Check the nrf52832's manual for their description.
+ */
+enum clock_registers {
+	TASKS_HFCLKSTART    = 0x000,
+	TASKS_HFCLKSTOP     = 0x004,
+	TASKS_LFCLKSTART    = 0x008,
+	TASKS_LFCLKSTOP     = 0x00c,
+	TASKS_CAL           = 0x010,
+	TASKS_CTSTART       = 0x014,
+	TASKS_CTSTOP        = 0x018,
+	EVENTS_HFCLKSTARTED = 0x100,
+	EVENTS_LFCLKSTARTED = 0x104,
+	EVENTS_DONE         = 0x10c,
+	EVENTS_CTTO         = 0x110,
+	INTENSET            = 0x304,
+	INTENCLR            = 0x308,
+	HFCLKRUN            = 0x408,
+	HFCLKSTAT           = 0x40c,
+	LFCLKRUN            = 0x414,
+	LFCLKSTAT           = 0x418,
+	LFCLKSRCCOPY        = 0x41c,
+	LFCLKSRC            = 0x518,
+	CTIV                = 0x538,
+	TRACECONFIG         = 0x55c,
+};
+
+static bool init_hfclk() {
+	/* We just assert that the source clock is running with the CPU internal clock
+     * as source */
+	u32 hfclk_status = READ_CLK_REG(HFCLKSTAT);
+	int clk_src = hfclk_status & 0x1;
+	bool clk_running = (hfclk_status >> 16) & 0x1;
+
+	return (clk_src == HFINT) && clk_running;
+}
+
+static bool init_lfclk() {
+	bool clk_started = false;
+	enum lfclk_src src = LFRC;
+
+	/* LFCLK use the LFRC clock by default, so it should be ready
+     * to be started directly */
+	WRITE_CLK_REG(TASKS_LFCLKSTART, 0x1);
+
+	/* Wait for the LFCLK to be started */
+	/* TODO: We should rely on the IRQ for the LFCLKSTARTED event instead */
+	do {
+		u32 lfclk_stat = READ_CLK_REG(LFCLKSTAT);
+
+		clk_started = (lfclk_stat >> 16) & 0x1;
+		src = lfclk_stat & 0x2;
+	} while (!clk_started);
+
+	return src == LFRC;
+}
+
+bool init_clock() {
+	return init_hfclk() && init_lfclk();
+}
diff --git a/src/clock.h b/src/clock.h
new file mode 100644
index 0000000..30cfb44
--- /dev/null
+++ b/src/clock.h
@@ -0,0 +1,10 @@
+#ifndef CLOCK_H
+#define CLOCK_H
+
+/**
+ * Init the nrf52832 CLOCK device and ensure that clock sources are correctly
+ * selected.
+ */
+bool init_clock();
+
+#endif
diff --git a/src/main.c b/src/main.c
index 62563e2..02c20f8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,4 +1,8 @@
+#include "clock.h"
+
 [[noreturn]]
 void main() {
+	init_clock();
+
 	while (1) {}
 }
-- 
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