diff --git a/src/stm32f4/clock.c b/src/stm32f4/clock.c
index b5fd16f8..e61fee53 100644
--- a/src/stm32f4/clock.c
+++ b/src/stm32f4/clock.c
@@ -1,10 +1,11 @@
-// Code to setup clocks on stm32f4
+// Code to setup clocks and gpio on stm32f4
 //
 // Copyright (C) 2019  Kevin O'Connor <kevin@koconnor.net>
 //
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
 #include "autoconf.h" // CONFIG_STM32F4_CLOCK_REF_8M
+#include "command.h" // DECL_CONSTANT_STR
 #include "internal.h" // enable_pclock
 
 #define FREQ_PERIPH (CONFIG_CLOCK_FREQ / 4)
@@ -52,6 +53,33 @@ get_pclock_frequency(uint32_t periph_base)
     return FREQ_PERIPH;
 }
 
+// Set the mode and extended function of a pin
+void
+gpio_peripheral(uint32_t gpio, uint32_t mode, int pullup)
+{
+    GPIO_TypeDef *regs = digital_regs[GPIO2PORT(gpio)];
+
+    // Enable GPIO clock
+    uint32_t rcc_pos = ((uint32_t)regs - AHB1PERIPH_BASE) / 0x400;
+    RCC->AHB1ENR |= (1<<rcc_pos);
+
+    // Configure GPIO
+    uint32_t mode_bits = mode & 0x0f, func = mode >> 4;
+    uint32_t pup = pullup ? (pullup > 0 ? 1 : 2) : 0;
+    uint32_t pos = gpio % 16, af_reg = pos / 8;
+    uint32_t af_shift = (pos % 8) * 4, af_msk = 0x0f << af_shift;
+    uint32_t m_shift = pos * 2, m_msk = 0x03 << m_shift;
+
+    regs->AFR[af_reg] = (regs->AFR[af_reg] & ~af_msk) | (func << af_shift);
+    regs->MODER = (regs->MODER & ~m_msk) | (mode_bits << m_shift);
+    regs->PUPDR = (regs->PUPDR & ~m_msk) | (pup << m_shift);
+    regs->OSPEEDR = (regs->OSPEEDR & ~m_msk) | (0x02 << m_shift);
+}
+
+#if CONFIG_STM32F4_CLOCK_REF_8M
+DECL_CONSTANT_STR("RESERVE_PINS_crystal", "PH0,PH1");
+#endif
+
 // Clock configuration
 static void
 enable_clock_stm32f40x(void)
@@ -127,9 +155,4 @@ clock_setup(void)
     RCC->CFGR = RCC_CFGR_PPRE1_DIV4 | RCC_CFGR_PPRE2_DIV4 | RCC_CFGR_SW_PLL;
     while ((RCC->CFGR & RCC_CFGR_SWS_Msk) != RCC_CFGR_SWS_PLL)
         ;
-
-    // Enable GPIO clocks
-    enable_pclock(GPIOA_BASE);
-    enable_pclock(GPIOB_BASE);
-    enable_pclock(GPIOC_BASE);
 }
diff --git a/src/stm32f4/gpio.c b/src/stm32f4/gpio.c
index 707eaf18..77a00c0f 100644
--- a/src/stm32f4/gpio.c
+++ b/src/stm32f4/gpio.c
@@ -14,28 +14,22 @@
 DECL_ENUMERATION_RANGE("pin", "PA0", GPIO('A', 0), 32);
 DECL_ENUMERATION_RANGE("pin", "PB0", GPIO('B', 0), 32);
 DECL_ENUMERATION_RANGE("pin", "PC0", GPIO('C', 0), 32);
+DECL_ENUMERATION_RANGE("pin", "PD0", GPIO('D', 0), 32);
+DECL_ENUMERATION_RANGE("pin", "PE0", GPIO('E', 0), 32);
+DECL_ENUMERATION_RANGE("pin", "PF0", GPIO('F', 0), 32);
+DECL_ENUMERATION_RANGE("pin", "PG0", GPIO('G', 0), 32);
+DECL_ENUMERATION_RANGE("pin", "PH0", GPIO('H', 0), 32);
+#ifdef GPIOI
+DECL_ENUMERATION_RANGE("pin", "PI0", GPIO('I', 0), 32);
+#endif
 
-static GPIO_TypeDef * const digital_regs[] = {
-    GPIOA, GPIOB, GPIOC
+GPIO_TypeDef * const digital_regs[] = {
+    GPIOA, GPIOB, GPIOC, GPIOD, GPIOE, GPIOF, GPIOG, GPIOH,
+#ifdef GPIOI
+    GPIOI,
+#endif
 };
 
-// Set the mode and extended function of a pin
-void
-gpio_peripheral(uint32_t gpio, uint32_t mode, int pullup)
-{
-    GPIO_TypeDef *regs = digital_regs[GPIO2PORT(gpio)];
-    uint32_t mode_bits = mode & 0x0f, func = mode >> 4;
-    uint32_t pup = pullup ? (pullup > 0 ? 1 : 2) : 0;
-    uint32_t pos = gpio % 16, af_reg = pos / 8;
-    uint32_t af_shift = (pos % 8) * 4, af_msk = 0x0f << af_shift;
-    uint32_t m_shift = pos * 2, m_msk = 0x03 << m_shift;
-
-    regs->AFR[af_reg] = (regs->AFR[af_reg] & ~af_msk) | (func << af_shift);
-    regs->MODER = (regs->MODER & ~m_msk) | (mode_bits << m_shift);
-    regs->PUPDR = (regs->PUPDR & ~m_msk) | (pup << m_shift);
-    regs->OSPEEDR = (regs->OSPEEDR & ~m_msk) | (0x02 << m_shift);
-}
-
 // Convert a register and bit location back to an integer pin identifier
 static int
 regs_to_pin(GPIO_TypeDef *regs, uint32_t bit)
@@ -47,11 +41,6 @@ regs_to_pin(GPIO_TypeDef *regs, uint32_t bit)
     return 0;
 }
 
-
-/****************************************************************
- * General Purpose Input Output (GPIO) pins
- ****************************************************************/
-
 struct gpio_out
 gpio_out_setup(uint32_t pin, uint32_t val)
 {
diff --git a/src/stm32f4/internal.h b/src/stm32f4/internal.h
index 062d7c65..22720a96 100644
--- a/src/stm32f4/internal.h
+++ b/src/stm32f4/internal.h
@@ -4,6 +4,8 @@
 
 #include "stm32f4xx.h"
 
+extern GPIO_TypeDef * const digital_regs[];
+
 #define GPIO(PORT, NUM) (((PORT)-'A') * 16 + (NUM))
 #define GPIO2PORT(PIN) ((PIN) / 16)
 #define GPIO2BIT(PIN) (1<<((PIN) % 16))