Atmel provided hardware specifics.

Demo/Common/drivers/Atmel/at91lib/peripherals/twi/twi.c

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+/* ----------------------------------------------------------------------------
+ *         ATMEL Microcontroller Software Support 
+ * ----------------------------------------------------------------------------
+ * Copyright (c) 2008, Atmel Corporation
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the disclaimer below.
+ *
+ * Atmel's name may not be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * DISCLAIMER: THIS SOFTWARE IS PROVIDED BY ATMEL "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT ARE
+ * DISCLAIMED. IN NO EVENT SHALL ATMEL BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
+ * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+ * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ * ----------------------------------------------------------------------------
+ */
+
+#ifndef trace_LEVEL
+    #define trace_LEVEL  1
+#endif
+
+//------------------------------------------------------------------------------
+//         Headers
+//------------------------------------------------------------------------------
+
+#include "twi.h"
+#include <utility/math.h>
+#include <utility/assert.h>
+#include <utility/trace.h>
+
+//------------------------------------------------------------------------------
+//         Global functions
+//------------------------------------------------------------------------------
+
+//------------------------------------------------------------------------------
+/// Configures a TWI peripheral to operate in master mode, at the given
+/// frequency (in Hz). The duty cycle of the TWI clock is set to 50%.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+/// \param twck  Desired TWI clock frequency.
+/// \param mck  Master clock frequency.
+//------------------------------------------------------------------------------
+void TWI_Configure(AT91S_TWI *pTwi, unsigned int twck, unsigned int mck)
+{
+    unsigned int ckdiv = 0;
+    unsigned int cldiv;
+    unsigned char ok = 0;
+
+    trace_LOG(trace_DEBUG, "-D- TWI_Configure()\n\r");
+    SANITY_CHECK(pTwi);
+
+    // Reset the TWI
+    pTwi->TWI_CR = AT91C_TWI_SWRST;
+
+    // Set master mode
+    pTwi->TWI_CR = AT91C_TWI_MSEN;
+
+    // Configure clock
+    while (!ok) {
+        
+        cldiv = ((mck / (2 * twck)) - 3) / power(2, ckdiv);
+        if (cldiv <= 255) {
+
+            ok = 1;
+        }
+        else {
+
+            ckdiv++;
+        }
+    }
+
+    ASSERT(ckdiv < 8, "-F- Cannot find valid TWI clock parameters\n\r");
+    trace_LOG(trace_INFO, "-D- Using CKDIV = %u and CLDIV/CHDIV = %u\n\r", ckdiv, cldiv);
+    pTwi->TWI_CWGR = (ckdiv << 16) | (cldiv << 8) | cldiv;
+}
+
+//------------------------------------------------------------------------------
+/// Sends a STOP condition on the TWI.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+//------------------------------------------------------------------------------
+void TWI_Stop(AT91S_TWI *pTwi)
+{
+    SANITY_CHECK(pTwi);
+
+    pTwi->TWI_CR = AT91C_TWI_STOP;
+}
+
+//------------------------------------------------------------------------------
+/// Starts a read operation on the TWI bus with the specified slave, and returns
+/// immediately. Data must then be read using TWI_ReadByte() whenever a byte is
+/// available (poll using TWI_ByteReceived()).
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+/// \param address  Slave address on the bus.
+/// \param iaddress  Optional internal address bytes.
+/// \param isize  Number of internal address bytes.
+//-----------------------------------------------------------------------------
+void TWI_StartRead(
+    AT91S_TWI *pTwi,
+    unsigned char address,
+    unsigned int iaddress,
+    unsigned char isize)
+{
+    trace_LOG(trace_DEBUG, "-D- TWI_StartRead()\n\r");
+    SANITY_CHECK(pTwi);
+    SANITY_CHECK((address & 0x80) == 0);
+    SANITY_CHECK((iaddress & 0xFF000000) == 0);
+    SANITY_CHECK(isize < 4);
+
+    // Set slave address and number of internal address bytes
+    pTwi->TWI_MMR = (isize << 8) | AT91C_TWI_MREAD | (address << 16);
+
+    // Set internal address bytes
+    pTwi->TWI_IADR = iaddress;
+
+    // Send START condition
+    pTwi->TWI_CR = AT91C_TWI_START;
+}
+
+//-----------------------------------------------------------------------------
+/// Reads a byte from the TWI bus. The read operation must have been started
+/// using TWI_StartRead() and a byte must be available (check with
+/// TWI_ByteReceived()).
+/// Returns the byte read.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+//-----------------------------------------------------------------------------
+unsigned char TWI_ReadByte(AT91S_TWI *pTwi)
+{
+    SANITY_CHECK(pTwi);
+
+    return pTwi->TWI_RHR;
+}
+
+//-----------------------------------------------------------------------------
+/// Sends a byte of data to one of the TWI slaves on the bus. This function
+/// must be called once before TWI_StartWrite() with the first byte of data
+/// to send, then it shall be called repeatedly after that to send the
+/// remaining bytes.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+/// \param byte  Byte to send.
+//-----------------------------------------------------------------------------
+void TWI_WriteByte(AT91S_TWI *pTwi, unsigned char byte)
+{
+    SANITY_CHECK(pTwi);
+
+    pTwi->TWI_THR = byte;
+}
+
+//-----------------------------------------------------------------------------
+/// Starts a write operation on the TWI to access the selected slave, then
+/// returns immediately. A byte of data must be provided to start the write;
+/// other bytes are written next.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+/// \param address  Address of slave to acccess on the bus.
+/// \param iaddress  Optional slave internal address.
+/// \param isize  Number of internal address bytes.
+/// \param byte  First byte to send.
+//-----------------------------------------------------------------------------
+void TWI_StartWrite(
+    AT91S_TWI *pTwi,
+    unsigned char address,
+    unsigned int iaddress,
+    unsigned char isize,
+    unsigned char byte)
+{
+    trace_LOG(trace_DEBUG, "-D- TWI_StartWrite()\n\r");
+    SANITY_CHECK(pTwi);
+    SANITY_CHECK((address & 0x80) == 0);
+    SANITY_CHECK((iaddress & 0xFF000000) == 0);
+    SANITY_CHECK(isize < 4);
+
+    // Set slave address and number of internal address bytes
+    pTwi->TWI_MMR = (isize << 8) | (address << 16);
+
+    // Set internal address bytes
+    pTwi->TWI_IADR = iaddress;
+
+    // Write first byte to send
+    TWI_WriteByte(pTwi, byte);
+}
+
+//-----------------------------------------------------------------------------
+/// Returns 1 if a byte has been received and can be read on the given TWI
+/// peripheral; otherwise, returns 0. This function resets the status register
+/// of the TWI.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+//-----------------------------------------------------------------------------
+unsigned char TWI_ByteReceived(AT91S_TWI *pTwi)
+{
+    return ((pTwi->TWI_SR & AT91C_TWI_RXRDY) == AT91C_TWI_RXRDY);
+}
+
+//-----------------------------------------------------------------------------
+/// Returns 1 if a byte has been sent, so another one can be stored for
+/// transmission; otherwise returns 0. This function clears the status register
+/// of the TWI.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+//-----------------------------------------------------------------------------
+unsigned char TWI_ByteSent(AT91S_TWI *pTwi)
+{
+    return ((pTwi->TWI_SR & AT91C_TWI_TXRDY) == AT91C_TWI_TXRDY);
+}
+
+//-----------------------------------------------------------------------------
+/// Returns 1 if the current transmission is complete (the STOP has been sent);
+/// otherwise returns 0.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+//-----------------------------------------------------------------------------
+unsigned char TWI_TransferComplete(AT91S_TWI *pTwi)
+{
+    return ((pTwi->TWI_SR & AT91C_TWI_TXCOMP) == AT91C_TWI_TXCOMP);
+}
+
+//-----------------------------------------------------------------------------
+/// Enables the selected interrupts sources on a TWI peripheral.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+/// \param sources  Bitwise OR of selected interrupt sources.
+//-----------------------------------------------------------------------------
+void TWI_EnableIt(AT91S_TWI *pTwi, unsigned int sources)
+{
+    SANITY_CHECK(pTwi);
+    SANITY_CHECK((sources & 0xFFFFFEF8) == 0);
+
+    pTwi->TWI_IER = sources;
+}
+
+//-----------------------------------------------------------------------------
+/// Disables the selected interrupts sources on a TWI peripheral.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+/// \param sources  Bitwise OR of selected interrupt sources.
+//-----------------------------------------------------------------------------
+void TWI_DisableIt(AT91S_TWI *pTwi, unsigned int sources)
+{
+    SANITY_CHECK(pTwi);
+    SANITY_CHECK((sources & 0xFFFFFEF8) == 0);
+
+    pTwi->TWI_IDR = sources;
+}
+
+//-----------------------------------------------------------------------------
+/// Returns the current status register of the given TWI peripheral. This
+/// resets the internal value of the status register, so further read may yield
+/// different values.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+//-----------------------------------------------------------------------------
+unsigned int TWI_GetStatus(AT91S_TWI *pTwi)
+{
+    SANITY_CHECK(pTwi);
+
+    return pTwi->TWI_SR;
+}
+
+//-----------------------------------------------------------------------------
+/// Returns the current status register of the given TWI peripheral, but
+/// masking interrupt sources which are not currently enabled.
+/// This resets the internal value of the status register, so further read may
+/// yield different values.
+/// \param pTwi  Pointer to an AT91S_TWI instance.
+//-----------------------------------------------------------------------------
+unsigned int TWI_GetMaskedStatus(AT91S_TWI *pTwi)
+{
+    unsigned int status;
+    
+    SANITY_CHECK(pTwi);
+    
+    status = pTwi->TWI_SR;
+    status &= pTwi->TWI_IMR;
+
+    return status;
+}
+