X-Git-Url: http://git.linex4red.de/pub/lufa.git/blobdiff_plain/88d022a75245e7492ecd11a5e1ea5c553acf0b2c..18b82b3575162c2c6d462c8f34a7d942f77a88ec:/LUFA/Drivers/Peripheral/AVR8/TWI_AVR8.h

diff --git a/LUFA/Drivers/Peripheral/AVR8/TWI_AVR8.h b/LUFA/Drivers/Peripheral/AVR8/TWI_AVR8.h
index 705ef530c..56697ff99 100644
--- a/LUFA/Drivers/Peripheral/AVR8/TWI_AVR8.h
+++ b/LUFA/Drivers/Peripheral/AVR8/TWI_AVR8.h
@@ -1,13 +1,13 @@
 /*
              LUFA Library
-     Copyright (C) Dean Camera, 2011.
+     Copyright (C) Dean Camera, 2012.
 
   dean [at] fourwalledcubicle [dot] com
            www.lufa-lib.org
 */
 
 /*
-  Copyright 2011  Dean Camera (dean [at] fourwalledcubicle [dot] com)
+  Copyright 2012  Dean Camera (dean [at] fourwalledcubicle [dot] com)
 
   Permission to use, copy, modify, distribute, and sell this
   software and its documentation for any purpose is hereby granted
@@ -52,8 +52,8 @@
  *
  *  <b>Low Level API Example:</b>
  *  \code
- *      // Initialize the TWI driver before first use
- *      TWI_Init(TWI_BIT_PRESCALE_1, 10);
+ *      // Initialize the TWI driver before first use at 200KHz
+ *      TWI_Init(TWI_BIT_PRESCALE_1, TWI_BITLENGTH_FROM_FREQ(1, 200000));
  *
  *      // Start a write session to device at device address 0xA0, internal address 0xDC with a 10ms timeout
  *      if (TWI_StartTransmission(0xA0 | TWI_ADDRESS_WRITE, 10) == TWI_ERROR_NoError)
@@ -88,11 +88,11 @@
  *          }
  *      }
  *  \endcode
- * 
+ *
  *  <b>High Level API Example:</b>
  *  \code
- *      // Initialize the TWI driver before first use
- *      TWI_Init(TWI_BIT_PRESCALE_1, 10);
+ *      // Initialize the TWI driver before first use at 200KHz
+ *      TWI_Init(TWI_BIT_PRESCALE_1, TWI_BITLENGTH_FROM_FREQ(1, 200000));
  *
  *      // Start a write session to device at device address 0xA0, internal address 0xDC with a 10ms timeout
  *      uint8_t InternalWriteAddress = 0xDC;
@@ -154,10 +154,10 @@
 			 *  or \ref TWI_ADDRESS_WRITE to obtain the device's read and write address respectively.
 			 */
 			#define TWI_DEVICE_ADDRESS_MASK  0xFE
-			
+
 			/** Bit length prescaler for \ref TWI_Init(). This mask multiplies the TWI bit length prescaler by 1. */
 			#define TWI_BIT_PRESCALE_1       ((0 << TWPS1) | (0 << TWPS0))
-			
+
 			/** Bit length prescaler for \ref TWI_Init(). This mask multiplies the TWI bit length prescaler by 4. */
 			#define TWI_BIT_PRESCALE_4       ((0 << TWPS1) | (1 << TWPS0))
 
@@ -166,7 +166,18 @@
 
 			/** Bit length prescaler for \ref TWI_Init(). This mask multiplies the TWI bit length prescaler by 64. */
 			#define TWI_BIT_PRESCALE_64      ((1 << TWPS1) | (1 << TWPS0))
-			
+
+			/** Calculates the length of each bit on the TWI bus for a given target frequency. This may be used with
+			 *  the \ref TWI_Init() function to convert a bus frequency to a number of clocks for the \c BitLength
+			 *  parameter.
+			 *
+			 *  \param[in] Prescale   Prescaler set on the TWI bus.
+			 *  \param[in] Frequency  Desired TWI bus frequency in Hz.
+			 *
+			 *  \return Bit length in clocks for the given TWI bus frequency at the given prescaler value.
+			 */
+			#define TWI_BITLENGTH_FROM_FREQ(Prescale, Frequency) ((((F_CPU / (Prescale)) / (Frequency)) - 16) / 2)
+
 		/* Enums: */
 			/** Enum for the possible return codes of the TWI transfer start routine and other dependant TWI functions. */
 			enum TWI_ErrorCodes_t
@@ -178,7 +189,7 @@
 				TWI_ERROR_SlaveNotReady        = 4, /**< Slave NAKed the TWI bus START condition. */
 				TWI_ERROR_SlaveNAK             = 5, /**< Slave NAKed whilst attempting to send data to the device. */
 			};
-	
+
 		/* Inline Functions: */
 			/** Initializes the TWI hardware into master mode, ready for data transmission and reception. This must be
 			 *  before any other TWI operations.
@@ -245,7 +256,7 @@
 			                     const bool LastByte) ATTR_NON_NULL_PTR_ARG(1);
 			bool TWI_ReceiveByte(uint8_t* const Byte,
 			                     const bool LastByte);
-					 
+
 			/** High level function to perform a complete packet transfer over the TWI bus to the specified
 			 *  device.
 			 *