i2c merge

9 files changed, 822 insertions, 1 deletions

diff --git a/libmaple/i2c.c b/libmaple/i2c.c
new file mode 100644
index 0000000..2064723
--- /dev/null
+++ b/libmaple/i2c.c
@@ -0,0 +1,502 @@
+/* *****************************************************************************
+ * The MIT License
+ *
+ * Copyright (c) 2010 Perry Hung.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ * ****************************************************************************/
+
+/**
+ *  @brief 
+ *  TODO: Rejigger hard fault handler and error throbs to turn off all
+ *  interrupts and jump to error throb to reenable usb bootloader
+ */
+
+#include "libmaple.h"
+#include "rcc.h"
+#include "nvic.h"
+#include "gpio.h"
+#include "nvic.h"
+#include "i2c.h"
+#include "string.h"
+
+/* 2/17 Started 10pm-4am
+ * 2/19 Started 7pm-2am
+ * 2/20 Started 7pm-7pm
+ * 2/23 Started 8pm */
+
+static inline int32 wait_for_state_change(i2c_dev *dev, i2c_state state);
+
+i2c_dev i2c_dev1 = {
+    .regs         = (i2c_reg_map*)I2C1_BASE,
+    .gpio_port    = GPIOB_BASE,
+    .sda_pin      = 7,
+    .scl_pin      = 6,
+    .clk_line     = RCC_I2C1,
+    .ev_nvic_line = NVIC_I2C1_EV,
+    .er_nvic_line = NVIC_I2C1_ER,
+    .state        = I2C_STATE_IDLE
+};
+
+/**
+ * @brief IRQ handler for i2c master. Handles transmission/reception.
+ * @param dev i2c device
+ */
+
+void delay_us(uint32 us) {
+    /* So (2^32)/12 micros max, or less than 6 minutes */
+    us *= 12;
+
+    /* fudge for function call overhead */
+    us--;
+    asm volatile("   mov r0, %[us]          \n\t"
+            "1: subs r0, #1            \n\t"
+            "   bhi 1b                 \n\t"
+            :
+            : [us] "r" (us)
+            : "r0");
+}
+static inline void debug_toggle(uint32 delay) {
+    gpio_write_bit(GPIOA_BASE, 5, 1);
+    delay_us(delay);
+    gpio_write_bit(GPIOA_BASE, 5, 0);
+}
+
+struct crumb {
+    uint32 event;
+    uint32 sr1;
+    uint32 sr2;
+};
+
+static struct crumb crumbs[100];
+static uint32 cur_crumb = 0;
+
+static inline void leave_big_crumb(uint32 event, uint32 sr1, uint32 sr2) {
+    if (cur_crumb < 100) {
+        struct crumb *crumb = &crumbs[cur_crumb++];
+        crumb->event = event;
+        crumb->sr1 = sr1;
+        crumb->sr2 = sr2;
+    }
+}
+
+enum {
+    IRQ_ENTRY           = 1,
+    TXE_ONLY            = 2,
+    TXE_BTF             = 3,
+    STOP_SENT           = 4,
+    TEST                = 5,
+    RX_ADDR_START       = 6,
+    RX_ADDR_STOP        = 7,
+    RXNE_ONLY           = 8,
+    RXNE_SENDING        = 9,
+    RXNE_START_SENT     = 10,
+    RXNE_STOP_SENT      = 11,
+    RXNE_DONE           = 12,
+};
+
+static void i2c_irq_handler(i2c_dev *dev) {
+    i2c_msg *msg = dev->msg;
+
+    uint8 read = msg->flags & I2C_MSG_READ;
+
+    uint32 sr1 = dev->regs->SR1;
+    uint32 sr2 = dev->regs->SR2;
+    leave_big_crumb(IRQ_ENTRY, sr1, sr2);
+
+    /*
+     * EV5: Start condition sent
+     */
+    if (sr1 & I2C_SR1_SB) {
+        msg->xferred = 0;
+        i2c_enable_irq(dev->regs, I2C_IRQ_BUFFER);
+
+        /*
+         * Master receiver
+         */
+        if (read) {
+            i2c_enable_ack(dev->regs);
+        }
+        i2c_send_slave_addr(dev->regs, msg->addr, read);
+        sr1 = sr2 = 0;
+    }
+
+    /*
+     * EV6: Slave address sent
+     */
+    if (sr1 & I2C_SR1_ADDR) {
+        /*
+         * Special case event EV6_1 for master receiver.
+         * Generate NACK and restart/stop condition after ADDR
+         * is cleared.
+         */
+        if (read) {
+            if (msg->length == 1) {
+                i2c_disable_ack(dev->regs);
+                dev->msgs_left--;
+                if (dev->msgs_left) {
+                    i2c_start_condition(dev->regs);
+                    leave_big_crumb(RX_ADDR_START, 0, 0);
+                } else {
+                    i2c_stop_condition(dev->regs);
+                    leave_big_crumb(RX_ADDR_STOP, 0, 0);
+                }
+            }
+        } else {
+            /*
+             * Master transmitter: write first byte to fill shift register.
+             * We should get another TXE interrupt immediately to fill DR again.
+             */
+            i2c_write(dev->regs, msg->data[msg->xferred++]);
+        }
+        sr1 = sr2 = 0;
+    }
+
+    /*
+     * EV8: Master transmitter
+     * Transmit buffer empty, but we haven't finished transmitting the last
+     * byte written.
+     */
+    if ((sr1 & I2C_SR1_TXE) && !(sr1 & I2C_SR1_BTF)) {
+        leave_big_crumb(TXE_ONLY, 0, 0);
+        if (dev->msgs_left) {
+            i2c_write(dev->regs, msg->data[msg->xferred++]);
+            if (msg->xferred == msg->length) {
+                /*
+                 * End of this message. Turn off TXE/RXNE and wait for
+                 * BTF to send repeated start or stop condition.
+                 */
+                i2c_disable_irq(dev->regs, I2C_IRQ_BUFFER);
+                dev->msgs_left--;
+            }
+        } else {
+            /*
+             * This should be impossible...
+             */
+            throb();
+        }
+        sr1 = sr2 = 0;
+    }
+
+    /*
+     * EV8_2: Master transmitter
+     * Last byte sent, program repeated start/stop
+     */
+    if ((sr1 & I2C_SR1_TXE) && (sr1 & I2C_SR1_BTF)) {
+        leave_big_crumb(TXE_BTF, 0, 0);
+        if (dev->msgs_left) {
+            leave_big_crumb(TEST, 0, 0);
+            /*
+             * Repeated start insanity: We can't disable ITEVTEN or else SB
+             * won't interrupt, but if we don't disable ITEVTEN, BTF will
+             * continually interrupt us. What the fuck ST?
+             */
+            i2c_start_condition(dev->regs);
+            while (!(dev->regs->SR1 & I2C_SR1_SB))
+                ;
+            dev->msg++;
+        } else {
+            i2c_stop_condition(dev->regs);
+            /*
+             * Turn off event interrupts to keep BTF from firing until the end
+             * of the stop condition. Why on earth they didn't have a start/stop
+             * condition request clear BTF is beyond me.
+             */
+            i2c_disable_irq(dev->regs, I2C_IRQ_EVENT);
+            leave_big_crumb(STOP_SENT, 0, 0);
+            dev->state = I2C_STATE_XFER_DONE;
+        }
+        sr1 = sr2 = 0;
+    }
+
+    /*
+     * EV7: Master Receiver
+     */
+    if (sr1 & I2C_SR1_RXNE) {
+        leave_big_crumb(RXNE_ONLY, 0, 0);
+        msg->data[msg->xferred++] = dev->regs->DR;
+
+        /*
+         * EV7_1: Second to last byte in the reception? Set NACK and generate
+         * stop/restart condition in time for the last byte. We'll get one more
+         * RXNE interrupt before shutting things down.
+         */
+        if (msg->xferred == (msg->length - 1)) {
+            i2c_disable_ack(dev->regs);
+            if (dev->msgs_left > 2) {
+                i2c_start_condition(dev->regs);
+                leave_big_crumb(RXNE_START_SENT, 0, 0);
+            } else {
+                i2c_stop_condition(dev->regs);
+                leave_big_crumb(RXNE_STOP_SENT, 0, 0);
+            }
+        } else if (msg->xferred == msg->length) {
+            dev->msgs_left--;
+            if (dev->msgs_left == 0) {
+                /*
+                 * We're done.
+                 */
+                leave_big_crumb(RXNE_DONE, 0, 0);
+                dev->state = I2C_STATE_XFER_DONE;
+            } else {
+                dev->msg++;
+            }
+        }
+    }
+}
+
+void I2C1_EV_IRQHandler(void) {
+   i2c_dev *dev = I2C1;
+   i2c_irq_handler(dev);
+}
+
+static void i2c_bus_reset(i2c_dev *dev) {
+    /* Release both lines */
+    gpio_write_bit(dev->gpio_port, dev->scl_pin, 1);
+    gpio_write_bit(dev->gpio_port, dev->sda_pin, 1);
+    gpio_set_mode(dev->gpio_port, dev->scl_pin, GPIO_MODE_OUTPUT_OD);
+    gpio_set_mode(dev->gpio_port, dev->sda_pin, GPIO_MODE_OUTPUT_OD);
+
+    /*
+     * Make sure the bus is free by clocking it until any slaves release the
+     * bus.
+     */
+    while (!gpio_read_bit(dev->gpio_port, dev->sda_pin)) {
+        /* Wait for any clock stretching to finish */
+        while (!gpio_read_bit(dev->gpio_port, dev->scl_pin))
+            ;
+        delay_us(10);
+
+        /* Pull low */
+        gpio_write_bit(dev->gpio_port, dev->scl_pin, 0);
+        delay_us(10);
+
+        /* Release high again */
+        gpio_write_bit(dev->gpio_port, dev->scl_pin, 1);
+        delay_us(10);
+    }
+
+    /* Generate start then stop condition */
+    gpio_write_bit(dev->gpio_port, dev->sda_pin, 0);
+    delay_us(10);
+    gpio_write_bit(dev->gpio_port, dev->scl_pin, 0);
+    delay_us(10);
+    gpio_write_bit(dev->gpio_port, dev->scl_pin, 1);
+    delay_us(10);
+    gpio_write_bit(dev->gpio_port, dev->sda_pin, 1);
+}
+
+/**
+ * @brief Initialize an i2c device as bus master
+ * @param device to enable
+ * @param flags bitwise or of the following I2C options:
+ *      I2C_FAST_MODE: 400 khz operation
+ *      I2C_10BIT_ADDRESSING: Enable 10-bit addressing
+ */
+void i2c_master_enable(i2c_dev *dev, uint32 flags) {
+#define STANDARD_CCR           (PCLK1/(100000*2))
+#define STANDARD_TRISE         37
+    /* Reset the bus. Clock out any hung slaves. */
+    i2c_bus_reset(dev);
+
+    /* Turn on clock and set GPIO modes */
+    rcc_reset_dev(dev->clk_line);
+    rcc_clk_enable(dev->clk_line);
+    gpio_set_mode(dev->gpio_port, dev->sda_pin, GPIO_MODE_AF_OUTPUT_OD);
+    gpio_set_mode(dev->gpio_port, dev->scl_pin, GPIO_MODE_AF_OUTPUT_OD);
+
+    /* I2C1 and I2C2 are fed from APB1, clocked at 36MHz */
+    i2c_set_input_clk(dev->regs, 36);
+
+    /* 100 khz only for now */
+    i2c_set_clk_control(dev->regs, STANDARD_CCR);
+
+    /*
+     * Set scl rise time, standard mode for now.
+     * Max rise time in standard mode: 1000 ns
+     * Max rise time in fast mode: 300ns
+     */
+    i2c_set_trise(dev->regs, STANDARD_TRISE);
+
+    /* Enable event and buffer interrupts */
+    nvic_irq_enable(dev->ev_nvic_line);
+    i2c_enable_irq(dev->regs, I2C_IRQ_EVENT | I2C_IRQ_BUFFER);
+
+    /*
+     * Important STM32 Errata:
+     *
+     * See STM32F10xx8 and STM32F10xxB Errata sheet (Doc ID 14574 Rev 8),
+     * Section 2.11.1, 2.11.2.
+     *
+     * 2.11.1:
+     * When the EV7, EV7_1, EV6_1, EV6_3, EV2, EV8, and EV3 events are not
+     * managed before the current byte is being transferred, problems may be
+     * encountered such as receiving an extra byte, reading the same data twice
+     * or missing data.
+     *
+     * 2.11.2:
+     * In Master Receiver mode, when closing the communication using
+     * method 2, the content of the last read data can be corrupted.
+     *
+     * If the user software is not able to read the data N-1 before the STOP
+     * condition is generated on the bus, the content of the shift register
+     * (data N) will be corrupted. (data N is shifted 1-bit to the left).
+     *
+     * ----------------------------------------------------------------------
+     *
+     * In order to ensure that events are not missed, the i2c interrupt must
+     * not be preempted. We set the i2c interrupt priority to be the highest
+     * interrupt in the system (priority level 0). All other interrupts have
+     * been initialized to priority level 16. See nvic_init().
+     */
+    nvic_irq_set_priority(dev->ev_nvic_line, 0);
+
+    /* Make it go! */
+    i2c_peripheral_enable(dev->regs);
+}
+
+
+int32 i2c_master_xfer(i2c_dev *dev, i2c_msg *msgs, uint16 num) {
+    int32 rc;
+    static int times = 0;
+
+    dev->msg = msgs;
+    dev->msgs_left = num;
+
+    memset(crumbs, 0, sizeof crumbs);
+
+    dev->regs->CR2 |= I2C_CR2_ITEVTEN;
+
+    /* Is this necessary? */
+    while (dev->regs->SR2 & I2C_SR2_BUSY)
+        ;
+
+    dev->state = I2C_STATE_BUSY;
+
+    i2c_start_condition(dev->regs);
+    rc = wait_for_state_change(dev, I2C_STATE_XFER_DONE);
+    if (rc < 0) {
+        goto out;
+    }
+
+    dev->state = I2C_STATE_IDLE;
+    rc = num;
+out:
+    return rc;
+}
+
+static inline int32 wait_for_state_change(i2c_dev *dev, i2c_state state) {
+    int32 rc;
+    i2c_state tmp;
+
+    while (1) {
+        tmp = dev->state;
+        if ((tmp == state) || (tmp == I2C_STATE_ERROR)) {
+            return (tmp == I2C_STATE_ERROR) ? -1 : 0;
+        }
+    }
+}
+
+
+/*
+ * Low level register twiddling functions
+ */
+
+/**
+ * @brief turn on an i2c peripheral
+ * @param map i2c peripheral register base
+ */
+void i2c_peripheral_enable(i2c_reg_map *regs) {
+    regs->CR1 |= I2C_CR1_PE;
+}
+
+/**
+ * @brief turn off an i2c peripheral
+ * @param map i2c peripheral register base
+ */
+void i2c_peripheral_disable(i2c_reg_map *regs) {
+    regs->CR1 &= ~I2C_CR1_PE;
+}
+
+/**
+ * @brief Set input clock frequency, in mhz
+ * @param device to configure
+ * @param freq frequency in megahertz (2-36)
+ */
+void i2c_set_input_clk(i2c_reg_map *regs, uint32 freq) {
+    uint32 cr2 = regs->CR2;
+    cr2 &= ~I2C_CR2_FREQ;
+    cr2 |= freq;
+    regs->CR2 = freq;
+}
+
+void i2c_set_clk_control(i2c_reg_map *regs, uint32 val) {
+    uint32 ccr = regs->CCR;
+    ccr &= ~I2C_CCR_CCR;
+    ccr |= val;
+    regs->CCR = ccr;
+}
+
+void i2c_set_fast_mode(i2c_reg_map *regs) {
+    regs->CCR |= I2C_CCR_FS;
+}
+
+void i2c_set_standard_mode(i2c_reg_map *regs) {
+    regs->CCR &= ~I2C_CCR_FS;
+}
+
+/**
+ * @brief Set SCL rise time
+ * @param
+ */
+
+void i2c_set_trise(i2c_reg_map *regs, uint32 trise) {
+    regs->TRISE = trise;
+}
+
+void i2c_start_condition(i2c_reg_map *regs) {
+    regs->CR1 |= I2C_CR1_START;
+}
+
+void i2c_stop_condition(i2c_reg_map *regs) {
+    regs->CR1 |= I2C_CR1_STOP;
+}
+
+void i2c_send_slave_addr(i2c_reg_map *regs, uint32 addr, uint32 rw) {
+    regs->DR = (addr << 1) | rw;
+}
+
+void i2c_enable_irq(i2c_reg_map *regs, uint32 irqs) {
+    regs->CR2 |= irqs;
+}
+
+void i2c_disable_irq(i2c_reg_map *regs, uint32 irqs) {
+    regs->CR2 &= ~irqs;
+}
+
+void i2c_enable_ack(i2c_reg_map *regs) {
+    regs->CR1 |= I2C_CR1_ACK;
+}
+
+void i2c_disable_ack(i2c_reg_map *regs) {
+    regs->CR1 &= ~I2C_CR1_ACK;
+}
+
+
+
diff --git a/libmaple/i2c.h b/libmaple/i2c.h
new file mode 100644
index 0000000..2e6d00d
--- /dev/null
+++ b/libmaple/i2c.h
@@ -0,0 +1,172 @@
+/* *****************************************************************************
+ * The MIT License
+ *
+ * Copyright (c) 2010 Perry Hung.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ * ****************************************************************************/
+
+/**
+ *  @brief libmaple i2c header
+ */
+
+#ifndef _I2C_H_
+#define _I2C_H_
+
+typedef struct i2c_reg_map {
+    __io uint32 CR1;
+    __io uint32 CR2;
+    __io uint32 OAR1;
+    __io uint32 OAR2;
+    __io uint32 DR;
+    __io uint32 SR1;
+    __io uint32 SR2;
+    __io uint32 CCR;
+    __io uint32 TRISE;
+} i2c_reg_map;
+
+typedef enum i2c_state {
+    I2C_STATE_IDLE,
+    I2C_STATE_XFER_DONE,
+    I2C_STATE_BUSY,
+    I2C_STATE_ERROR             = -1
+} i2c_state;
+
+typedef struct i2c_msg {
+    uint16 addr;
+#define I2C_MSG_READ            0x1
+#define I2C_MSG_10BIT_ADDR      0x2
+    uint16 flags;
+    uint16 length;
+    uint16 xferred;
+    uint8 *data;
+} i2c_msg;
+
+typedef struct i2c_dev {
+    i2c_reg_map *regs;
+    GPIO_Port *gpio_port;
+    uint8 sda_pin;
+    uint8 scl_pin;
+    uint8 clk_line;
+    uint8 ev_nvic_line;
+    uint8 er_nvic_line;
+    volatile uint8 state;
+    uint16 msgs_left;
+    i2c_msg *msg;
+} i2c_dev;
+
+
+extern i2c_dev i2c_dev1;
+extern i2c_dev i2c_dev2;
+
+#define I2C1                    (i2c_dev*)&i2c_dev1
+#define I2C2                    (i2c_dev*)&i2c_dev2
+
+#define I2C1_BASE               0x40005400
+#define I2C2_BASE               0x40005800
+
+/* i2c enable options */
+#define I2C_FAST_MODE           0x1             // 400 khz
+#define I2C_DUTY_16_9           0x2             // 16/9 duty ratio
+
+/* Control register 1 bits */
+#define I2C_CR1_SWRST           BIT(15)         // Software reset
+#define I2C_CR1_ALERT           BIT(13)         // SMBus alert
+#define I2C_CR1_PEC             BIT(12)         // Packet error checking
+#define I2C_CR1_POS             BIT(11)         // Acknowledge/PEC position
+#define I2C_CR1_ACK             BIT(10)         // Acknowledge enable
+#define I2C_CR1_START           BIT(8)          // Start generation
+#define I2C_CR1_STOP            BIT(9)          // Stop generation
+#define I2C_CR1_PE              BIT(0)          // Peripheral Enable
+
+/* Control register 2 bits */
+#define I2C_CR2_LAST            BIT(12)         // DMA last transfer
+#define I2C_CR2_DMAEN           BIT(11)         // DMA requests enable
+#define I2C_CR2_ITBUFEN         BIT(10)         // Buffer interrupt enable
+#define I2C_CR2_ITEVTEN         BIT(9)          // Event interupt enable
+#define I2C_CR2_ITERREN         BIT(8)          // Error interupt enable
+#define I2C_CR2_FREQ            0xFFF           // Peripheral input frequency
+
+/* Clock control register bits */
+#define I2C_CCR_FS              BIT(15)         // Master mode selection
+#define I2C_CCR_CCR             0xFFF           // Clock control bits
+
+/* Status register 1 bits  */
+#define I2C_SR1_SB              BIT(0)          // Start bit
+#define I2C_SR1_ADDR            BIT(1)          // Address sent/matched
+#define I2C_SR1_BTF             BIT(2)          // Byte transfer finished
+#define I2C_SR1_ADD10           BIT(3)          // 10-bit header sent
+#define I2C_SR1_STOPF           BIT(4)          // Stop detection
+#define I2C_SR1_RXNE            BIT(6)          // Data register not empty
+#define I2C_SR1_TXE             BIT(7)          // Data register empty
+#define I2C_SR1_BERR            BIT(8)          // Bus error
+#define I2C_SR1_ARLO            BIT(9)          // Arbitration lost
+#define I2C_SR1_AF              BIT(10)         // Acknowledge failure
+#define I2C_SR1_OVR             BIT(11)         // Overrun/underrun
+#define I2C_SR1_PECERR          BIT(12)         // PEC Error in reception
+#define I2C_SR1_TIMEOUT         BIT(14)         // Timeout or Tlow error
+#define I2C_SR1_SMBALERT        BIT(15)         // SMBus alert
+
+/* Status register 2 bits */
+#define I2C_SR2_MSL             BIT(0)          // Master/slave
+#define I2C_SR2_BUSY            BIT(1)          // Bus busy
+#define I2C_SR2_TRA             BIT(2)          // Transmitter/receiver
+#define I2C_SR2_GENCALL         BIT(4)          // General call address
+#define I2C_SR2_SMBDEFAULT      BIT(5)          // SMBus device default address
+#define I2C_SR2_SMBHOST         BIT(6)          // SMBus host header
+#define I2C_SR2_DUALF           BIT(7)          // Dual flag
+#define I2C_SR2_PEC             0xFF00          // Packet error checking register
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void i2c_master_enable(i2c_dev *dev, uint32 flags);
+int32 i2c_master_xfer(i2c_dev *dev, i2c_msg *msgs, uint16 num);
+
+void i2c_start_condition(i2c_reg_map *regs);
+void i2c_stop_condition(i2c_reg_map *regs);
+void i2c_send_slave_addr(i2c_reg_map *regs, uint32 addr, uint32 rw);
+void i2c_set_input_clk(i2c_reg_map *regs, uint32 freq);
+void i2c_set_clk_control(i2c_reg_map *regs, uint32 val);
+void i2c_set_fast_mode(i2c_reg_map *regs);
+void i2c_set_standard_mode(i2c_reg_map *regs);
+void i2c_set_trise(i2c_reg_map *regs, uint32 trise);
+void i2c_enable_ack(i2c_reg_map *regs);
+void i2c_disable_ack(i2c_reg_map *regs);
+
+/* interrupt flags */
+#define I2C_IRQ_ERROR              I2C_CR2_ITERREN
+#define I2C_IRQ_EVENT              I2C_CR2_ITEVTEN
+#define I2C_IRQ_BUFFER             I2C_CR2_ITBUFEN
+void i2c_enable_irq(i2c_reg_map *regs, uint32 irqs);
+void i2c_disable_irq(i2c_reg_map *regs, uint32 irqs);
+void i2c_peripheral_enable(i2c_reg_map *regs);
+void i2c_peripheral_disable(i2c_reg_map *regs);
+
+static inline void i2c_write(i2c_reg_map *regs, uint8 byte) {
+    regs->DR = byte;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+
diff --git a/libmaple/nvic.c b/libmaple/nvic.c
index b1da605..28ca169 100644
--- a/libmaple/nvic.c
+++ b/libmaple/nvic.c
@@ -27,6 +27,7 @@
  */
 
 #include "libmaple.h"
+#include "scb.h"
 #include "nvic.h"
 #include "systick.h"
 
@@ -64,11 +65,32 @@ void nvic_irq_disable_all(void) {
     __write(NVIC_ICER1, 0xFFFFFFFF);
 }
 
+
+/**
+ * @brief Set interrupt priority for an interrupt line
+ *      Note: The STM32 only implements 4 bits of priority, ignoring
+ *      the lower 4 bits. This means there are only 16 levels of priority.
+ *      Bits[3:0] read as zero and ignore writes.
+ * @param irqn device to set
+ * @param priority priority to set, 0 being highest priority and 15 being
+ * lowest.
+ */
+void nvic_irq_set_priority(int32 irqn, uint8 priority) {
+    if (irqn < 0) {
+        /* This interrupt is in the system handler block  */
+        SCB->SHP[((uint32)irqn & 0xF) - 4] = (priority & 0xF) << 4;
+    } else {
+        NVIC->IP[irqn] = (priority & 0xF) << 4;
+    }
+}
+
 /**
  * @brief Initialize the NVIC according to VECT_TAB_FLASH,
  * VECT_TAB_RAM, or VECT_TAB_BASE.
  */
 void nvic_init(void) {
+    uint32 i;
+
 #ifdef VECT_TAB_FLASH
     nvic_set_vector_table(USER_ADDR_ROM, 0x0);
 #elif defined VECT_TAB_RAM
@@ -78,4 +100,15 @@ void nvic_init(void) {
 #else
 #error "You must set a base address for the vector table!"
 #endif
+
+    /*
+     * Lower priority level for all peripheral interrupts to lowest
+     * possible.
+     */
+    for (i = 0; i < NR_INTERRUPTS; i++) {
+        nvic_irq_set_priority(i, 0xF);
+    }
+
+    /* Lower systick interrupt priority to lowest level */
+    nvic_irq_set_priority(NVIC_SYSTICK, 0xF);
 }
diff --git a/libmaple/nvic.h b/libmaple/nvic.h
index 6004c36..fe9990f 100644
--- a/libmaple/nvic.h
+++ b/libmaple/nvic.h
@@ -47,10 +47,43 @@ extern "C"{
 #define NVIC_ICER1          0xE000E184
 /* NVIC_ICER2 only on connectivity line */
 
+/* NVIC Priority  */
+#define NVIC_PRI_BASE       0xE000E400
+
 /* System control registers  */
 #define SCB_VTOR            0xE000ED08  // Vector table offset register
 
+#define NVIC_VectTab_RAM             ((u32)0x20000000)
+#define NVIC_VectTab_FLASH           ((u32)0x08000000)
+
+#define NVIC_BASE           0xE000E100
+#define NVIC                ((nvic_reg_map*)NVIC_BASE)
+
+typedef struct nvic_reg_map {
+  __io uint32 ISER[8];                 // Interrupt Set Enable Registers
+       uint32 RESERVED0[24];
+  __io uint32 ICER[8];                 // Interrupt Clear Enable Registers
+       uint32 RSERVED1[24];
+  __io uint32 ISPR[8];                 // Interrupt Set Pending Registers
+       uint32 RESERVED2[24];
+  __io uint32 ICPR[8];                 // Interrupt Clear Pending Registers
+       uint32 RESERVED3[24];
+  __io uint32 IABR[8];                 // Interrupt Active bit Registers
+       uint32 RESERVED4[56];
+  __io uint8  IP[240];                 // Interrupt Priority Registers
+       uint32 RESERVED5[644];
+  __io uint32 STIR;                    // Software Trigger Interrupt Registers
+} nvic_reg_map;
+
 enum {
+    NVIC_NMI          = -14,
+    NVIC_MEM_MANAGE   = -12,
+    NVIC_BUS_FAULT    = -11,
+    NVIC_USAGE_FAULT  = -10,
+    NVIC_SVC          = -5,
+    NVIC_DEBUG_MON    = -4,
+    NVIC_PEND_SVC     = -2,
+    NVIC_SYSTICK      = -1,
     NVIC_TIMER1       = 27,
     NVIC_TIMER2       = 28,
     NVIC_TIMER3       = 29,
@@ -80,7 +113,12 @@ enum {
     NVIC_DMA_CH4      = 14,
     NVIC_DMA_CH5      = 15,
     NVIC_DMA_CH6      = 16,
-    NVIC_DMA_CH7      = 17
+    NVIC_DMA_CH7      = 17,
+
+    NVIC_I2C1_EV      = 31,
+    NVIC_I2C1_ER      = 32,
+    NVIC_I2C2_EV      = 33,
+    NVIC_I2C2_ER      = 34
 };
 
 
@@ -91,6 +129,7 @@ void nvic_init(void);
 void nvic_irq_enable(uint32 device);
 void nvic_irq_disable(uint32 device);
 void nvic_irq_disable_all(void);
+void nvic_set_priority(int32 irqn, uint8 priority);
 
 #ifdef __cplusplus
 }
diff --git a/libmaple/rcc.c b/libmaple/rcc.c
index 2841af3..d3fb6a3 100644
--- a/libmaple/rcc.c
+++ b/libmaple/rcc.c
@@ -76,6 +76,8 @@ static const struct rcc_dev_info rcc_dev_table[] = {
     [RCC_DMA2]   = { .clk_domain = AHB,  .line_num = 1 }, // High-density only
     [RCC_PWR]    = { .clk_domain = APB1, .line_num = 28},
     [RCC_BKP]    = { .clk_domain = APB1, .line_num = 27}
+    [RCC_I2C1]   = { .clk_domain = APB1, .line_num = 21 }, // High-density only
+    [RCC_I2C2]   = { .clk_domain = APB1, .line_num = 22 }, // High-density only
 };
 
 /**
diff --git a/libmaple/rcc.h b/libmaple/rcc.h
index 410ab8b..569da57 100644
--- a/libmaple/rcc.h
+++ b/libmaple/rcc.h
@@ -180,6 +180,8 @@ typedef enum {
     RCC_DMA2,        // High-density devices only (Maple Native)
     RCC_PWR,
     RCC_BKP,
+    RCC_I2C1,
+    RCC_I2C2
 } rcc_clk_id;
 
 
diff --git a/libmaple/rules.mk b/libmaple/rules.mk
index b87595d..3d8171f 100644
--- a/libmaple/rules.mk
+++ b/libmaple/rules.mk
@@ -22,6 +22,7 @@ cSRCS_$(d) := adc.c                    \
               gpio.c                   \
               iwdg.c                   \
               nvic.c                   \
+              i2c.c                    \
               rcc.c                    \
               spi.c                    \
               syscalls.c               \
diff --git a/libmaple/scb.h b/libmaple/scb.h
new file mode 100644
index 0000000..f851a08
--- /dev/null
+++ b/libmaple/scb.h
@@ -0,0 +1,58 @@
+/* *****************************************************************************
+ * The MIT License
+ *
+ * Copyright (c) 2010 Perry Hung.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ * ****************************************************************************/
+
+/**
+ *  @brief System control block header
+ */
+
+#ifndef _SCB_H_
+#define _SCB_H_
+
+typedef struct scb_reg_map {
+  __io uint32 CPUID;            // CPU ID Base Register
+  __io uint32 ICSR;             // Interrupt Control State Register
+  __io uint32 VTOR;             // Vector Table Offset Register
+  __io uint32 AIRCR;            // Application Interrupt / Reset Control Register
+  __io uint32 SCR;              // System Control Register
+  __io uint32 CCR;              // Configuration Control Register
+  __io uint8  SHP[12];          // System Handlers Priority Registers (4-7, 8-11, 12-15)
+  __io uint32 SHCSR;            // System Handler Control and State Register
+  __io uint32 CFSR;             // Configurable Fault Status Register
+  __io uint32 HFSR;             // Hard Fault Status Register
+  __io uint32 DFSR;             // Debug Fault Status Register
+  __io uint32 MMFAR;            // Mem Manage Address Register
+  __io uint32 BFAR;             // Bus Fault Address Register
+  __io uint32 AFSR;             // Auxiliary Fault Status Register
+  __io uint32 PFR[2];           // Processor Feature Register
+  __io uint32 DFR;              // Debug Feature Register
+  __io uint32 ADR;              // Auxiliary Feature Register
+  __io uint32 MMFR[4];          // Memory Model Feature Register
+  __io uint32 ISAR[5];          // ISA Feature Register
+} scb_reg_map;
+
+#define SCB_BASE            0xE000ED00
+#define SCB                 ((scb_reg_map*)(SCB_BASE))
+
+#endif
+
diff --git a/libmaple/stm32.h b/libmaple/stm32.h
new file mode 100644
index 0000000..e65b28c
--- /dev/null
+++ b/libmaple/stm32.h
@@ -0,0 +1,12 @@
+/**
+ *  @brief General STM32 specific definitions
+ */
+
+#ifndef _STM32_H_
+#define _STM32_H_
+
+#define PCLK1   36000000U
+#define PCLK2   72000000U
+
+#endif
+