From 3a69e75d9ace0cc3d752e5ed7e2149009ac34078 Mon Sep 17 00:00:00 2001
From: Alexander Heldt <me@alexanderheldt.se>
Date: Wed, 1 Jan 2025 12:23:18 +0100
Subject: [PATCH] Add `gpio_set_af` to set alternative function of a pin

---
 src/gpio.c | 12 ++++++++++++
 src/gpio.h |  1 +
 2 files changed, 13 insertions(+)

diff --git a/src/gpio.c b/src/gpio.c
index b92dd26..fa63bb9 100644
--- a/src/gpio.c
+++ b/src/gpio.c
@@ -10,6 +10,18 @@ void gpio_set_mode(uint16_t pin, GPIO_MODE mode) {
   gpio->MODER |= (mode & 0b11) << (pn * 2);   // Set new mode. Each pin uses 2 bits
 }
 
+void gpio_set_af(uint16_t pin, uint8_t af) {
+  struct gpio *gpio = GPIO(PINPORT(pin));
+  int pn = PINNUM(pin);
+  if (pn < 8) {
+	gpio->AFRL &= ~(0b1111 << (pn * 4)); // Each pin uses 4 bits
+	gpio->AFRL |= (af & 0b1111) << (pn * 4);
+  } else {
+	gpio->AFRH &= ~(0b1111 << (pn * 4)); // Each pin uses 4 bits
+	gpio->AFRH |= (af & 0b1111) << (pn * 4);
+  }
+}
+
 void gpio_write(uint16_t pin, bool val) {
   struct gpio *gpio = GPIO(PINPORT(pin));
   gpio->BSRR = (0b0011 << PINNUM(pin)) << (val ? 0 : 16);
diff --git a/src/gpio.h b/src/gpio.h
index bad0e48..298fd88 100644
--- a/src/gpio.h
+++ b/src/gpio.h
@@ -38,6 +38,7 @@ typedef enum {
 } GPIO_MODE;
 
 void gpio_set_mode(uint16_t pin, GPIO_MODE mode);
+void gpio_set_af(uint16_t pin, uint8_t af);
 void gpio_write(uint16_t pin, bool val);
 
 #endif