diff --git a/pwm.c b/pwm.c
new file mode 100644
index 0000000..bcc2e1b
--- /dev/null
+++ b/pwm.c
@@ -0,0 +1,21 @@
+#include <hardware/pwm.h>
+#include <pico/types.h>
+
+#include "const.h"
+
+#include "pwm.h"
+
+void pwm_isr(void) {
+	static uint slice = -1, chan = -1;
+	if (slice == -1) slice = pwm_gpio_to_slice_num(AUDIO_OUT);
+	if (chan == -1) chan = pwm_gpio_to_channel(AUDIO_OUT);
+
+	pwm_clear_irq(slice);
+
+	// TODO:
+	float sample = 0.0f;
+
+	uint16_t level = (uint16_t)((sample + 1.0f) * 0.5f * 3400.0f);
+	pwm_set_chan_level(slice, chan, level);
+}
+
diff --git a/pwm.h b/pwm.h
new file mode 100644
index 0000000..7a5fae3
--- /dev/null
+++ b/pwm.h
@@ -0,0 +1,4 @@
+#pragma once
+
+void pwm_isr(void);
+