Handle starting/ending reads/writes to I2C

src/usci-i2c.cpp

@@ -4,20 +4,26 @@ namespace mardev::msp430::usci::i2c
 {
     namespace usci = mardev::msp430::usci;
 
-    void __send_signal(const uint8_t signal_mask)
-    {
-        *usci::registers::UCB0CTL1 |= signal_mask;
-        while(*usci::registers::UCB0CTL1 & signal_mask);
-
-        return;
-    }
-
-    void read_begin()
+    bool read_begin()
     {
+        // Set receive mode and generate the start condition.
         *usci::registers::UCB0CTL1 ^= registers::masks::UCTR;
-        start();
+        __start();
 
-        return;
+        // Wait to be ACKed or NACKed.
+        while(*usci::registers::UCB0CTL1 & registers::masks::UCTXSTT);
+
+        // Read starts without any other intervention.
+        // Checking UCTXNACK will discern an issue with communication.
+        if(*usci::registers::UCB0STAT ^ registers::masks::UCNACKIFG)
+        {
+            return true;
+        }
+        else
+        {
+            __stop();
+            return false;
+        }
     }
 
     uint8_t read()
@@ -27,12 +33,30 @@ namespace mardev::msp430::usci::i2c
         return *usci::registers::UCB0RXBUF;
     }
 
-    void write_begin()
+    uint8_t read_end()
     {
+        __stop();
+        return *usci::registers::UCB0RXBUF;
+    }
+
+    bool write_begin()
+    {
+        // Set transmit mode and generate the start condition.
         *usci::registers::UCB0CTL1 |= registers::masks::UCTR;
-        start();
+        __start();
 
-        return;
+        // Wait to be ACKed or NACKed.
+        while(*usci::registers::UCB0CTL1 & registers::masks::UCTXSTT);
+
+        if(*interrupt::registers::IFG2 & usci::registers::masks::UCB0TXIFG)
+        {
+            return true;
+        }
+        else
+        {
+            __stop();
+            return false;
+        }
     }
 
     void write(const uint8_t data)

src/usci-i2c.h

@@ -123,13 +123,15 @@ namespace mardev::msp430::usci::i2c
         *registers::UCB0I2CSA = address;
     }
 
-    void __send_signal(const uint8_t signal_mask);
+    inline void __send_signal(const uint8_t signal_mask) { *usci::registers::UCB0CTL1 |= signal_mask; }
 
     inline void __nack() { __send_signal(registers::masks::UCTXNACK); }
 
-    inline void stop() { __send_signal(registers::masks::UCTXSTP); }
+    /** Issue a stop condition.
+     */
+    inline void __stop() { __send_signal(registers::masks::UCTXSTP); }
 
-    inline void start() { __send_signal(registers::masks::UCTXSTT); }
+    inline void __start() { __send_signal(registers::masks::UCTXSTT); }
 
     /** Returns true if the I2C clock signal is held low.
      */
@@ -161,9 +163,12 @@ namespace mardev::msp430::usci::i2c
 
     /** Start a read from a peripheral.
      *
-     * The peripheral address needs to be set with set_periph_address() or set_periph_address10() before calling this function.
+     * The peripheral address needs to be set prior.
+     * See set_periph_address() or set_periph_address10().
+     *
+     * \returns True if reception is ready to begin.
      */
-    void read_begin();
+    bool read_begin();
 
     /** Read a byte from the peripheral.
      *
@@ -174,18 +179,32 @@ namespace mardev::msp430::usci::i2c
      */
     uint8_t read();
 
+    /** End a read from a peripheral.
+     *
+     * Generates a stop condition to end a read.
+     * \returns The last byte read from the peripheral.
+     */
+    uint8_t read_end();
+
     /** Start a write to a peripheral.
      *
-     * The peripheral address needs to be set with set_periph_address() or set_periph_address10() before calling this function.
+     * The peripheral address needs to be set.
+     * See set_periph_address() and set_periph_address10().
+     *
+     * \returns True if transmission is ready to begin.
      */
-    void write_begin();
+    bool write_begin();
 
     /** Write a byte to the peripheral.
      *
      * Synchronously writes a byte to the peripheral.
      * A write must have been started with write_begin() before calling this function.
      */
     void write(const uint8_t data);
+
+    /** End a write from a peripheral.
+     */
+    inline void write_end() { __stop(); }
 }
 
 #endif