ETH97J60.c

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// ////////////////////////////////////////////////////////////////////////////
// ////////////////////////////////////////////////////////////////////////////
/*********************************************************************
 * Software License Agreement
 *
 * Copyright (C) 2002-2008 Microchip Technology Inc.  All rights 
 * reserved.
 *
 * Microchip licenses to you the right to use, modify, copy, and 
 * distribute: 
 * (i)  the Software when embedded on a Microchip microcontroller or 
 *      digital signal controller product ("Device") which is 
 *      integrated into Licensee's product; or
 * (ii) ONLY the Software driver source files ENC28J60.c and 
 *      ENC28J60.h ported to a non-Microchip device used in 
 *      conjunction with a Microchip ethernet controller for the 
 *      sole purpose of interfacing with the ethernet controller. 
 *
 * You should refer to the license agreement accompanying this 
 * Software for additional information regarding your rights and 
 * obligations.
 *
 * THE SOFTWARE AND DOCUMENTATION ARE PROVIDED "AS IS" WITHOUT 
 * WARRANTY OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT 
 * LIMITATION, ANY WARRANTY OF MERCHANTABILITY, FITNESS FOR A 
 * PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT SHALL 
 * MICROCHIP BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT OR 
 * CONSEQUENTIAL DAMAGES, LOST PROFITS OR LOST DATA, COST OF 
 * PROCUREMENT OF SUBSTITUTE GOODS, TECHNOLOGY OR SERVICES, ANY CLAIMS 
 * BY THIRD PARTIES (INCLUDING BUT NOT LIMITED TO ANY DEFENSE 
 * THEREOF), ANY CLAIMS FOR INDEMNITY OR CONTRIBUTION, OR OTHER 
 * SIMILAR COSTS, WHETHER ASSERTED ON THE BASIS OF CONTRACT, TORT 
 * (INCLUDING NEGLIGENCE), BREACH OF WARRANTY, OR OTHERWISE.
 *
 *
/*********************************************************************
 * Author               Date     Comment
 *~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 * Rawin Rojvanit       07/26/05 Stuff
 * Howard Schlunder     11/17/05 Ported to PIC18F97J60
 * Howard Schlunder     06/16/06 Synchronized with ENC28J60 code
 * Howard Schlunder     05/21/07 Fixed a TX lockup problem
********************************************************************/
#define __ETH97J60_C

#include "TCPIP.h"

// MODIFIX: Removed the macro request for the ethernet transceiver.


// Since the Ethernet PHY doesn't support auto-negotiation, full-duplex mode is 
// not compatible with most switches/routers.  If a dedicated network is used 
// where the duplex of the remote node can be manually configured, you may 
// change this configuration.  Otherwise, half duplex should always be used.
#define HALF_DUPLEX
//#define FULL_DUPLEX

// Pseudo Functions
#define LOW(a)                  (a & 0xFF)
#define HIGH(a)                 ((a>>8) & 0xFF)

#define ETHER_IP    (0x00u)
#define ETHER_ARP   (0x06u)

// A header appended at the start of all RX frames by the hardware
typedef struct _ENC_PREAMBLE
{
    WORD            NextPacketPointer;
    RXSTATUS        StatusVector;

    MAC_ADDR        DestMACAddr;
    MAC_ADDR        SourceMACAddr;
    WORD_VAL        Type;
} ENC_PREAMBLE;


// Internal MAC level variables and flags.
static WORD_VAL NextPacketLocation;
static WORD_VAL CurrentPacketLocation;
static BOOL WasDiscarded;
static WORD wTXWatchdog;


/******************************************************************************
 * Function:        void MACInit(void)
 *
 * PreCondition:    None
 *
 * Input:           None
 *
 * Output:          None
 *
 * Side Effects:    None
 *
 * Overview:        MACInit enables the Ethernet module, waits for the 
 *                  to become ready, and programs all registers for future 
 *                  TX/RX operations.
 *
 * Note:            This function blocks for at least 1ms, waiting for the 
 *                  hardware to stabilize.
 *****************************************************************************/
void MACInit(void)
{
    BYTE i;
    
    LATAbits.LATA0 = 0;
    LATAbits.LATA1 = 0;

    TRISAbits.TRISA0 = 0;   // Set LED0 as output
    TRISAbits.TRISA1 = 0;   // Set LED1 as output
    ECON2bits.ETHEN = 1;    // Enable Ethernet!

    // Wait for PHYRDY to become set.
    while(!ESTATbits.PHYRDY);
    
    // Configure the receive buffer boundary pointers 
    // and the buffer write protect pointer (receive buffer read pointer)
    WasDiscarded = TRUE;
    NextPacketLocation.Val = RXSTART;
    ERXST = RXSTART;
    ERXRDPTL = LOW(RXSTOP); // Write low byte first
    ERXRDPTH = HIGH(RXSTOP);// Write high byte last
    ERXND = RXSTOP;
    ETXST = TXSTART;

    // Write a permanant per packet control byte of 0x00
    EWRPT = TXSTART;
    MACPut(0x00);

    // Configure Receive Filters 
    // (No need to reconfigure - Unicast OR Broadcast with CRC checking is 
    // acceptable)
    //ERXFCON = ERXFCON_CRCEN;     // Promiscious mode
    ERXFCON = 0xA3;             // MODIFIX: Enable Multicasts

    // Configure the MAC
    // Enable the receive portion of the MAC
    MACON1 = MACON1_TXPAUS | MACON1_RXPAUS | MACON1_MARXEN; Nop();

    // Pad packets to 60 bytes, add CRC, and check Type/Length field.
#if defined(FULL_DUPLEX)
    MACON3 = MACON3_PADCFG0 | MACON3_TXCRCEN | MACON3_FRMLNEN | MACON3_FULDPX; Nop();
    MABBIPG = 0x15; Nop();
#else
    MACON3 = MACON3_PADCFG0 | MACON3_TXCRCEN | MACON3_FRMLNEN; Nop();
    MABBIPG = 0x12; Nop();
#endif

    // Allow infinite deferals if the medium is continuously busy 
    // (do not time out a transmission if the half duplex medium is 
    // completely saturated with other people's data)
    MACON4 = MACON4_DEFER; Nop();

    // Set non-back-to-back inter-packet gap to 9.6us.  The back-to-back 
    // inter-packet gap (MABBIPG) is set by MACSetDuplex() which is called 
    // later.
    MAIPGL = 0x12; Nop();
    MAIPGH = 0x0C; Nop();

    // Set the maximum packet size which the controller will accept
    MAMXFLL = LOW(6+6+2+1500+4); Nop();
    MAMXFLH = HIGH(6+6+2+1500+4); Nop();
    
    // MODIFIX: Initialize physical MAC address registers from flash.
    MAADR1 = pu8MAC[0]; Nop();
    MAADR2 = pu8MAC[1]; Nop();
    MAADR3 = pu8MAC[2]; Nop();
    MAADR4 = pu8MAC[3]; Nop();
    MAADR5 = pu8MAC[4]; Nop();
    MAADR6 = pu8MAC[5]; Nop();

    // Disable half duplex loopback in PHY and set RXAPDIS bit as per errata 
    WritePHYReg(PHCON2, PHCON2_HDLDIS | PHCON2_RXAPDIS);

    // Configure LEDA to display LINK status, LEDB to display TX/RX activity
    SetLEDConfig(0x3472);
    
    // Set the PHY into the proper duplex state
#if defined(FULL_DUPLEX)
    WritePHYReg(PHCON1, PHCON1_PDPXMD);
#else
    WritePHYReg(PHCON1, 0x0000);
#endif

    // Enable packet reception
    ECON1bits.RXEN = 1;
}//end MACInit


/******************************************************************************
 * Function:        BOOL MACIsLinked(void)
 *
 * PreCondition:    None
 *
 * Input:           None
 *
 * Output:          TRUE: If the PHY reports that a link partner is present 
 *                        and the link has been up continuously since the last 
 *                        call to MACIsLinked()
 *                  FALSE: If the PHY reports no link partner, or the link went 
 *                         down momentarily since the last call to MACIsLinked()
 *
 * Side Effects:    None
 *
 * Overview:        Returns the PHSTAT1.LLSTAT bit.
 *
 * Note:            None
 *****************************************************************************/
/*BOOL MACIsLinked(void)
{
    // LLSTAT is a latching low link status bit.  Therefore, if the link 
    // goes down and comes back up before a higher level stack program calls
    // bMACIsLinked(), bMACIsLinked() will still return FALSE.  The next 
    // call to MACIsLinked() will return TRUE (unless the link goes down 
    // again).
    return ReadPHYReg(PHSTAT1).PHSTAT1bits.LLSTAT;
}
*/
BOOL MACIsLinked( void )
{
    // MODIFIX: We simply check the link status LED, whether there is a link.
    return PORTAbits.RA0;
}

/******************************************************************************
 * Function:        BOOL MACIsTxReady(void)
 *
 * PreCondition:    None
 *
 * Input:           None
 *
 * Output:          TRUE: If no Ethernet transmission is in progress
 *                  FALSE: If a previous transmission was started, and it has 
 *                         not completed yet.  While FALSE, the data in the 
 *                         transmit buffer and the TXST/TXND pointers must not
 *                         be changed.
 *
 * Side Effects:    None
 *
 * Overview:        Returns the ECON1.TXRTS bit
 *
 * Note:            None
 *****************************************************************************/
BOOL MACIsTxReady(void)
{
    if(!ECON1bits.TXRTS)
        return TRUE;

    // Retry transmission if the current packet seems to be not completing
    // Wait 3ms before triggering the retry.
    if((WORD)TickGet() - wTXWatchdog >= (3ull*TICK_SECOND/1000ull))
    {
        ECON1bits.TXRTS = 0;
        MACFlush();
    }
    
    return FALSE;
}

/******************************************************************************
 * Function:        void MACDiscardRx(void)
 *
 * PreCondition:    None
 *
 * Input:           None
 *
 * Output:          None
 *
 * Side Effects:    None
 *
 * Overview:        Marks the last received packet (obtained using 
 *                  MACGetHeader())as being processed and frees the buffer 
 *                  memory associated with it
 *
 * Note:            Is is safe to call this function multiple times between 
 *                  MACGetHeader() calls.  Extra packets won't be thrown away 
 *                  until MACGetHeader() makes it available.
 *****************************************************************************/
void MACDiscardRx(void)
{
    WORD_VAL NewRXRDLocation;

    // Make sure the current packet was not already discarded
    if(WasDiscarded)
        return;
    WasDiscarded = TRUE;

    // Decrement the next packet pointer before writing it into 
    // the ERXRDPT registers.  This is a silicon errata workaround.
    // RX buffer wrapping must be taken into account if the 
    // NextPacketLocation is precisely RXSTART.
    NewRXRDLocation.Val = NextPacketLocation.Val - 1;
#if RXSTART == 0
    if(NewRXRDLocation.Val > RXSTOP)
#else
    if(NewRXRDLocation.Val < RXSTART || NewRXRDLocation.Val > RXSTOP)
#endif
    {
        NewRXRDLocation.Val = RXSTOP;
    }

    // Decrement the RX packet counter register, EPKTCNT
    ECON2bits.PKTDEC = 1;

    // Move the receive read pointer to unwrite-protect the memory used by the 
    // last packet.  The writing order is important: set the low byte first, 
    // high byte last.
    ERXRDPTL = NewRXRDLocation.v[0];
    ERXRDPTH = NewRXRDLocation.v[1];
    
    // The PKTIF flag should automatically be cleared by hardware, but 
    // early beta silicon requires that you manually clear it.  This should be 
    // unneeded for production A0 silicon and later.
    EIRbits.PKTIF = 0;
}


/******************************************************************************
 * Function:        WORD MACGetFreeRxSize(void)
 *
 * PreCondition:    None
 *
 * Input:           None
 *
 * Output:          A WORD estimate of how much RX buffer space is free at 
 *                  the present time.
 *
 * Side Effects:    None
 *
 * Overview:        None
 *
 * Note:            None
 *****************************************************************************/
WORD MACGetFreeRxSize(void)
{
    WORD_VAL ReadPT, WritePT;

    // Read the Ethernet hardware buffer write pointer.  Because packets can be 
    // received at any time, it can change between reading the low and high 
    // bytes.  A loop is necessary to make certain a proper low/high byte pair
    // is read.
    do {
        // Save EPKTCNT in a temporary location
        ReadPT.v[0] = EPKTCNT;
    
        WritePT.Val = ERXWRPT;  
    } while(EPKTCNT != ReadPT.v[0]);
    
    // Determine where the write protection pointer is
    ReadPT.Val = ERXRDPT;

    
    // Calculate the difference between the pointers, taking care to account 
    // for buffer wrapping conditions
    if(WritePT.Val > ReadPT.Val)
    {
        return (RXSTOP - RXSTART) - (WritePT.Val - ReadPT.Val);
    }
    else if(WritePT.Val == ReadPT.Val)
    {
        return RXSIZE - 1;
    }
    else
    {
        return ReadPT.Val - WritePT.Val - 1;
    }
}

/******************************************************************************
 * Function:        BOOL MACGetHeader(MAC_ADDR *remote, BYTE* type)
 *
 * PreCondition:    None
 *
 * Input:           *remote: Location to store the Source MAC address of the 
 *                           received frame.
 *                  *type: Location of a BYTE to store the constant 
 *                         MAC_UNKNOWN, ETHER_IP, or ETHER_ARP, representing 
 *                         the contents of the Ethernet type field.
 *
 * Output:          TRUE: If a packet was waiting in the RX buffer.  The 
 *                        remote, and type values are updated.
 *                  FALSE: If a packet was not pending.  remote and type are 
 *                         not changed.
 *
 * Side Effects:    Last packet is discarded if MACDiscardRx() hasn't already
 *                  been called.
 *
 * Overview:        None
 *
 * Note:            None
 *****************************************************************************/
BOOL MACGetHeader(MAC_ADDR *remote, BYTE* type)
{
    ENC_PREAMBLE header;

    // Test if at least one packet has been received and is waiting
    if(EPKTCNT == 0u)
    {
        return FALSE;
    }

    // Make absolutely certain that any previous packet was discarded
    if(WasDiscarded == FALSE)
    {
        MACDiscardRx();
        return FALSE;
    }
    // Save the location of this packet
    CurrentPacketLocation.Val = NextPacketLocation.Val;

    // Set the read pointer to the beginning of the next unprocessed packet
    ERDPT = CurrentPacketLocation.Val;

    // Obtain the MAC header from the Ethernet buffer
    MACGetArray((BYTE*)&header, sizeof(header));

    // The EtherType field, like most items transmitted on the Ethernet medium
    // are in big endian.
    header.Type.Val = swaps(header.Type.Val);

    // Do a sanity check.  There might be a bug in code someplace if this 
    // Reset() ever happens.  Check for potential errors in array/pointer writing code.
    if(header.NextPacketPointer > RXSTOP || ((BYTE_VAL*)(&header.NextPacketPointer))->bits.b0 ||
       header.StatusVector.bits.Zero ||
       header.StatusVector.bits.CRCError ||
       header.StatusVector.bits.ByteCount > 1518u ||
       !header.StatusVector.bits.ReceiveOk)
    {
        Reset();
    }

    // Save the location where the hardware will write the next packet to
    NextPacketLocation.Val = header.NextPacketPointer;

    // Return the Ethernet frame's Source MAC address field to the caller
    // This parameter is useful for replying to requests without requiring an 
    // ARP cycle.
    memcpy((void*)remote->v, (void*)header.SourceMACAddr.v, sizeof(*remote));

    // Return a simplified version of the EtherType field to the caller
    *type = MAC_UNKNOWN;
    if( (header.Type.v[1] == 0x08u) && 
        ((header.Type.v[0] == ETHER_IP) || (header.Type.v[0] == ETHER_ARP)) )
    {
        *type = header.Type.v[0];
    }

    // Mark this packet as discardable
    WasDiscarded = FALSE;   
    return TRUE;
}


/******************************************************************************
 * Function:        void MACPutHeader(MAC_ADDR *remote, BYTE type, WORD dataLen)
 *
 * PreCondition:    MACIsTxReady() must return TRUE.
 *
 * Input:           *remote: Pointer to memory which contains the destination
 *                           MAC address (6 bytes)
 *                  type: The constant ETHER_ARP or ETHER_IP, defining which 
 *                        value to write into the Ethernet header's type field.
 *                  dataLen: Length of the Ethernet data payload
 *
 * Output:          None
 *
 * Side Effects:    None
 *
 * Overview:        None
 *
 * Note:            Because of the dataLen parameter, it is probably 
 *                  advantagous to call this function immediately before 
 *                  transmitting a packet rather than initially when the 
 *                  packet is first created.  The order in which the packet
 *                  is constructed (header first or data first) is not 
 *                  important.
 *****************************************************************************/
void MACPutHeader(MAC_ADDR *remote, BYTE type, WORD dataLen)
{
    // Set the write pointer to the beginning of the transmit buffer
    EWRPT = TXSTART + 1;

    // Calculate where to put the TXND pointer
    dataLen += (WORD)sizeof(ETHER_HEADER) + TXSTART;

    // Write the TXND pointer into the registers, given the dataLen given
    ETXND = dataLen;

    // Set the per-packet control byte and write the Ethernet destination 
    // address
    MACPutArray((BYTE*)remote, sizeof(*remote));

    // MODIFIX: Write our MAC address from flash in the Ethernet source field
    MACPutROMArray( ( ROM BYTE * ) pu8MAC, sizeof( MAC_ADDR ) );

    // Write the appropriate Ethernet Type WORD for the protocol being used
    MACPut(0x08);
    MACPut((type == MAC_IP) ? ETHER_IP : ETHER_ARP);
}

/******************************************************************************
 * Function:        void MACFlush(void)
 *
 * PreCondition:    A packet has been created by calling MACPut() and 
 *                  MACPutHeader().
 *
 * Input:           None
 *
 * Output:          None
 *
 * Side Effects:    None
 *
 * Overview:        MACFlush causes the current TX packet to be sent out on 
 *                  the Ethernet medium.  The hardware MAC will take control
 *                  and handle CRC generation, collision retransmission and 
 *                  other details.
 *
 * Note:            After transmission completes (MACIsTxReady() returns TRUE), 
 *                  the packet can be modified and transmitted again by calling 
 *                  MACFlush() again.  Until MACPutHeader() or MACPut() is 
 *                  called (in the TX data area), the data in the TX buffer 
 *                  will not be corrupted.
 *****************************************************************************/
void MACFlush(void)
{
    // Reset the Ethernet TX logic.  This is a (suspected) errata workaround to 
    // prevent the TXRTS bit from getting stuck set indefinitely, causing the 
    // stack to lock up under certain bad conditions.
    ECON1bits.TXRST = 1;
    ECON1bits.TXRST = 0;    

    // Wait at least 1.6us after TX Reset before setting TXRTS.
    // If you don't wait long enough, the TX logic won't be finished resetting.
    {volatile BYTE i = 8; while(i--);}  
    EIRbits.TXERIF = 0;

    // Start the transmission
    // After transmission completes (MACIsTxReady() returns TRUE), the packet 
    // can be modified and transmitted again by calling MACFlush() again.
    // Until MACPutHeader() is called, the data in the TX buffer will not be 
    // corrupted.
    ECON1bits.TXRTS = 1;
    wTXWatchdog = TickGet();
}


/******************************************************************************
 * Function:        void MACSetReadPtrInRx(WORD offset)
 *
 * PreCondition:    A packet has been obtained by calling MACGetHeader() and 
 *                  getting a TRUE result.
 *
 * Input:           offset: WORD specifying how many bytes beyond the Ethernet 
 *                          header's type field to relocate the SPI read 
 *                          pointer.
 *
 * Output:          None
 *
 * Side Effects:    None
 *
 * Overview:        SPI read pointer are updated.  All calls to 
 *                  MACGet() and MACGetArray() will use these new values.
 *
 * Note:            RXSTOP must be statically defined as being > RXSTART for 
 *                  this function to work correctly.  In other words, do not 
 *                  define an RX buffer which spans the 0x1FFF->0x0000 memory
 *                  boundary.
 *****************************************************************************/
void MACSetReadPtrInRx(WORD offset)
{
    WORD_VAL ReadPT;

    // Determine the address of the beginning of the entire packet
    // and adjust the address to the desired location
    ReadPT.Val = CurrentPacketLocation.Val + sizeof(ENC_PREAMBLE) + offset;
    
    // Since the receive buffer is circular, adjust if a wraparound is needed
    if(ReadPT.Val > RXSTOP)
        ReadPT.Val -= RXSIZE;
    
    // Set the read pointer to the new calculated value
    ERDPTL = ReadPT.v[0];
    ERDPTH = ReadPT.v[1];
}

WORD_VAL u16MACGetCurrentReadPtrPos(void)
{
    WORD_VAL ReadPT;
    ReadPT.v[0] = ERDPTL;
    ReadPT.v[1] = ERDPTH;
    return ReadPT;
}

void MACSetCurrentReadPtrPos(WORD_VAL u16Pos)
{
    ERDPTL = u16Pos.v[0];
    ERDPTH = u16Pos.v[1];
}

/******************************************************************************
 * Function:        WORD MACSetWritePtr(WORD Address)
 *
 * PreCondition:    None
 *
 * Input:           Address: Address to seek to
 *
 * Output:          WORD: Old EWRPT location
 *
 * Side Effects:    None
 *
 * Overview:        SPI write pointer is updated.  All calls to 
 *                  MACPut() and MACPutArray() will use this new value.
 *
 * Note:            None
 *****************************************************************************/
WORD MACSetWritePtr(WORD address)
{
    WORD oldVal;

    oldVal = EWRPT;
    EWRPT = address;
    return oldVal;
}

/******************************************************************************
 * Function:        WORD MACSetReadPtr(WORD Address)
 *
 * PreCondition:    None
 *
 * Input:           Address: Address to seek to
 *
 * Output:          WORD: Old ERDPT value
 *
 * Side Effects:    None
 *
 * Overview:        SPI write pointer is updated.  All calls to 
 *                  MACPut() and MACPutArray() will use this new value.
 *
 * Note:            None
 *****************************************************************************/
WORD MACSetReadPtr(WORD address)
{
    WORD oldVal;

    oldVal = ERDPT;
    ERDPT = address;
    return oldVal;
}


/******************************************************************************
 * Function:        WORD MACCalcRxChecksum(WORD offset, WORD len)
 *
 * PreCondition:    None
 *
 * Input:           offset  - Number of bytes beyond the beginning of the 
 *                          Ethernet data (first byte after the type field) 
 *                          where the checksum should begin
 *                  len     - Total number of bytes to include in the checksum
 *
 * Output:          16-bit checksum as defined by RFC 793.
 *
 * Side Effects:    None
 *
 * Overview:        This function performs a checksum calculation in the MAC
 *                  buffer itself
 *
 * Note:            None
 *****************************************************************************/
WORD MACCalcRxChecksum(WORD offset, WORD len)
{
    WORD temp;
    WORD RDSave;

    // Add the offset requested by firmware plus the Ethernet header
    temp = CurrentPacketLocation.Val + sizeof(ENC_PREAMBLE) + offset;
    if(temp > RXSTOP)       // Adjust value if a wrap is needed
    {
        temp -= RXSIZE;
    }

    RDSave = ERDPT;
    ERDPT = temp;
    temp = CalcIPBufferChecksum(len);
    ERDPT = RDSave;

    return temp;
}


/******************************************************************************
 * Function:        WORD CalcIPBufferChecksum(WORD len)
 *
 * PreCondition:    Read buffer pointer set to starting of checksum data
 *
 * Input:           len: Total number of bytes to calculate the checksum over. 
 *                       The first byte included in the checksum is the byte 
 *                       pointed to by ERDPT, which is updated by calls to 
 *                       MACGet(), MACSetRxBuffer(), MACSetTxBuffer(), etc.
 *
 * Output:          16-bit checksum as defined by RFC 793
 *
 * Side Effects:    None
 *
 * Overview:        This function performs a checksum calculation in the MAC
 *                  buffer itself.  The MAC has a hardware DMA module 
 *                  which can calculate the checksum faster than software, so 
 *                  this function replaces the CaclIPBufferChecksum() function 
 *                  defined in the helpers.c file.  Through the use of 
 *                  preprocessor defines, this replacement is automatic.
 *
 * Note:            This function works either in the RX buffer area or the TX
 *                  buffer area.  No validation is done on the len parameter.
 *****************************************************************************/
/*
WORD CalcIPBufferChecksum(WORD len)
{
    WORD_VAL temp;

    // Take care of special cases which the DMA cannot be used for
    if(len == 0u)
    {
        return 0xFFFF;
    }
    else if(len == 1u)
    {
        return ~((WORD)MACGet());
    }
        

    // Set the DMA starting address to the RAM read pointer value
    temp.Val = ERDPT;
    EDMAST = temp.Val;
    
    // See if we are calculating a checksum within the RX buffer (where 
    // wrapping rules apply) or TX/unused area (where wrapping rules are 
    // not applied)
#if RXSTART == 0
    if(temp.Val <= RXSTOP)
#else
    if(temp.Val >= RXSTART && temp.Val <= RXSTOP)
#endif
    {
        // Calculate the DMA ending address given the starting address and len 
        // parameter.  The DMA will follow the receive buffer wrapping boundary.
        temp.Val += len-1;
        if(temp.Val > RXSTOP)
        {
            temp.Val -= RXSIZE;
        }
    }
    else
    {
        temp.Val += len-1;
    }   

    // Write the DMA end address
    EDMAND = temp.Val;
    
    // Begin the DMA checksum calculation and wait until it is finished
    ECON1bits.CSUMEN = 1;
    ECON1bits.DMAST = 1;
    while(ECON1bits.DMAST);

    // Return the resulting good stuff
    return (((WORD)EDMACSL)<<8) | EDMACSH;
}
*/

/******************************************************************************
 * Function:        WORD CalcIPBufferChecksum(WORD len)
 *
 * PreCondition:    Read buffer pointer set to starting of checksum data
 *
 * Input:           len: Total number of bytes to calculate the checksum over. 
 *                       The first byte included in the checksum is the byte 
 *                       pointed to by ERDPT, which is updated by calls to 
 *                       MACSetReadPtr(), MACGet(), MACGetArray(), 
 *                       MACGetHeader(), etc.
 *
 * Output:          16-bit checksum as defined by RFC 793
 *
 * Side Effects:    None
 *
 * Overview:        This function performs a checksum calculation in the MAC
 *                  buffer itself
 *
 * Note:            This function works either in the RX buffer area or the TX
 *                  buffer area.  No validation is done on the len parameter.
 *****************************************************************************/
WORD CalcIPBufferChecksum(WORD len)
{
    WORD Start;
    DWORD_VAL Checksum = {0x00000000ul};
    WORD ChunkLen;
    BYTE DataBuffer[20];    // Must be an even size
    WORD *DataPtr;

    // Save the read pointer starting address
    Start = ERDPT;

    while(len)
    {
        // Obtain a chunk of data (less SPI overhead compared 
        // to requesting one byte at a time)
        ChunkLen = len > sizeof(DataBuffer) ? sizeof(DataBuffer) : len;
        MACGetArray(DataBuffer, ChunkLen);

        len -= ChunkLen;

        // Take care of a last odd numbered data byte
        if(((WORD_VAL*)&ChunkLen)->bits.b0)
        {
            DataBuffer[ChunkLen] = 0x00;
            ChunkLen++;
        }

        // Calculate the checksum over this chunk
        DataPtr = (WORD*)&DataBuffer[0];
        while(ChunkLen)
        {
            Checksum.Val += *DataPtr++;
            ChunkLen -= 2;
        }
    }

    // Restore old read pointer location
    ERDPT = Start;
    
    // Do an end-around carry (one's complement arrithmatic)
    Checksum.Val = (DWORD)Checksum.w[0] + (DWORD)Checksum.w[1];

    // Do another end-around carry in case if the prior add 
    // caused a carry out
    Checksum.w[0] += Checksum.w[1];

    // Return the resulting checksum
    return ~Checksum.w[0];
}

/******************************************************************************
 * Function:        void MACMemCopyAsync(WORD destAddr, WORD sourceAddr, WORD len)
 *
 * PreCondition:    None
 *
 * Input:           destAddr:   Destination address in the Ethernet memory to 
 *                              copy to.  If the MSb is set, the current EWRPT 
 *                              value will be used instead.
 *                  sourceAddr: Source address to read from.  If the MSb is 
 *                              set, the current ERDPT value will be used 
 *                              instead.
 *                  len:        Number of bytes to copy
 *
 * Output:          None
 *
 * Side Effects:    None
 *
 * Overview:        Bytes are asynchrnously transfered within the buffer.  Call 
 *                  MACIsMemCopyDone() to see when the transfer is complete.  
 *
 * Note:            If a prior transfer is already in progress prior to 
 *                  calling this function, this function will block until it 
 *                  can start this transfer.
 *****************************************************************************/
void MACMemCopyAsync(WORD destAddr, WORD sourceAddr, WORD len)
{
    WORD_VAL ReadSave, WriteSave;
    BOOL UpdateWritePointer = FALSE;
    BOOL UpdateReadPointer = FALSE;

    if(((WORD_VAL*)&destAddr)->bits.b15)
    {
        UpdateWritePointer = TRUE;
        destAddr = EWRPT;
    }
    if(((WORD_VAL*)&sourceAddr)->bits.b15)
    {
        UpdateReadPointer = TRUE;
        sourceAddr = ERDPT;
    }

    // Handle special conditions where len == 0 or len == 1
    // The DMA module is not capable of handling those corner cases
    if(len <= 1u)
    {
        ReadSave.Val = ERDPT;
        WriteSave.Val = EWRPT;
        ERDPT = sourceAddr;
        EWRPT = destAddr;
        while(len--)
            MACPut(MACGet());
        if(!UpdateReadPointer)
        {
            ERDPT = ReadSave.Val;
        }
        if(!UpdateWritePointer)
        {
            EWRPT = WriteSave.Val;
        }
    }
    else
    {
        if(UpdateWritePointer)
        {
            WriteSave.Val = destAddr + len;
            EWRPT = WriteSave.Val;
        }
        len += sourceAddr - 1;
        while(ECON1bits.DMAST);
        EDMAST = sourceAddr;
        EDMADST = destAddr;
        if((sourceAddr <= RXSTOP) && (len > RXSTOP)) //&& (sourceAddr >= RXSTART))
            len -= RXSIZE;
        EDMAND = len;
        ECON1bits.CSUMEN = 0;
        ECON1bits.DMAST = 1;
        while(ECON1bits.DMAST);         // DMA errata workaround: Must not access EDATA while DMA active

        if(UpdateReadPointer)
        {
            len++;
            if((sourceAddr <= RXSTOP) && (len > RXSTOP)) //&& (sourceAddr >= RXSTART))
                len -= RXSIZE;
            ERDPT = len;
        }
    }
}

/*
void MACMemCopyAsync(WORD destAddr, WORD sourceAddr, WORD len)
{
    WORD_VAL ReadSave, WriteSave;
    BOOL UpdateWritePointer = FALSE;
    BOOL UpdateReadPointer = FALSE;

    if(((WORD_VAL*)&destAddr)->bits.b15)
    {
        UpdateWritePointer = TRUE;
        destAddr = EWRPT;
    }
    if(((WORD_VAL*)&sourceAddr)->bits.b15)
    {
        UpdateReadPointer = TRUE;
        sourceAddr = ERDPT;
    }

    ReadSave.Val = ERDPT;
    WriteSave.Val = EWRPT;
    ERDPT = sourceAddr;
    EWRPT = destAddr;
    while(len--)
    {
        MACPut(MACGet());
    }

    if(!UpdateReadPointer)
    {
        ERDPT = ReadSave.Val;
    }
    if(!UpdateWritePointer)
    {
        EWRPT = WriteSave.Val;
    }
}
*/

BOOL MACIsMemCopyDone(void)
{
    return !ECON1bits.DMAST;
}

/******************************************************************************
 * Function:        BYTE MACGet()
 *
 * PreCondition:    ERDPT must point to the place to read from.
 *
 * Input:           None
 *
 * Output:          Byte read from the Ethernet's buffer RAM
 *
 * Side Effects:    None
 *
 * Overview:        MACGet returns the byte pointed to by ERDPT and 
 *                  increments ERDPT so MACGet() can be called again.  The 
 *                  increment will follow the receive buffer wrapping boundary.
 *
 * Note:            For better performance, implement this function as a macro:
 *                  #define MACGet()    (EDATA)
 *****************************************************************************/
BYTE MACGet()
{
    return EDATA;
}//end MACGet


/******************************************************************************
 * Function:        WORD MACGetArray(BYTE *val, WORD len)
 *
 * PreCondition:    ERDPT must point to the place to read from.
 *
 * Input:           *val: Pointer to storage location
 *                  len:  Number of bytes to read from the data buffer.
 *
 * Output:          Byte(s) of data read from the data buffer.
 *
 * Side Effects:    None
 *
 * Overview:        Reads several sequential bytes from the data buffer 
 *                  and places them into local memory.  ERDPT is incremented 
 *                  after each byte, following the same rules as MACGet().
 *
 * Note:            None
 *****************************************************************************/
WORD MACGetArray(BYTE *val, WORD len)
{
    WORD w;
    volatile BYTE i;
    
    w = len;
    if(val)
    {
        while(w--)
        {
            *val++ = EDATA;
        }
    }
    else
    {
        while(w--)
        {
            i = EDATA;
        }
    }

    return len;
}//end MACGetArray


/******************************************************************************
 * Function:        void MACPut(BYTE val)
 *
 * PreCondition:    EWRPT must point to the location to begin writing.
 *
 * Input:           Byte to write into the Ethernet buffer memory
 *
 * Output:          None
 *
 * Side Effects:    None
 *
 * Overview:        Writes to the EDATA register, which will indirectly 
*                   increment EWRPTH:EWRPTL.
 *
 * Note:            None
 *****************************************************************************/
void MACPut(BYTE val)
{
    // Note:  Due to a PIC18F97J60 bug, you must use the MOVFF instruction to 
    // write to EDATA or else the read pointer (ERDPT) will inadvertently 
    // increment.
    PRODL = val;
    #if defined(HI_TECH_C)
        asm("movff  _PRODL, _EDATA");
    #else
        _asm movff  PRODL, EDATA _endasm
    #endif
}//end MACPut


/******************************************************************************
 * Function:        void MACPutArray(BYTE *val, WORD len)
 *
 * PreCondition:    EWRPT must point to the location to begin writing.
 *
 * Input:           *val: Pointer to source of bytes to copy.
 *                  len:  Number of bytes to write to the data buffer.
 *
 * Output:          None
 *
 * Side Effects:    None
 *
 * Overview:        MACPutArray writes several sequential bytes to the 
 *                  Ethernet buffer RAM.  It performs faster than multiple MACPut()
 *                  calls.  EWRPT is incremented by len.
 *
 * Note:            None
 *****************************************************************************/
void MACPutArray(BYTE *val, WORD len)
{
    while(len--)
    {
        // Note:  Due to a PIC18F97J60 bug, you must use the MOVFF instruction to 
        // write to EDATA or else the read pointer (ERDPT) will inadvertently 
        // increment.
        PRODL = *val++;
        #if defined(HI_TECH_C)
            asm("movff  _PRODL, _EDATA");
        #else
            _asm movff  PRODL, EDATA _endasm
        #endif
    }
}//end MACPutArray

void MACPutROMArray(ROM BYTE *val, WORD len)
{
    while(len--)
    {
        // Note:  Due to a PIC18F97J60 bug, you must use the MOVFF instruction to 
        // write to EDATA or else the read pointer (ERDPT) will inadvertently 
        // increment.
        PRODL = *val++;
        #if defined(HI_TECH_C)
            asm("movff  _PRODL, _EDATA");
        #else
            _asm movff  PRODL, EDATA _endasm
        #endif
    }
}//end MACPutROMArray


/******************************************************************************
 * Function:        ReadPHYReg
 *
 * PreCondition:    Ethernet module must be enabled (ECON1.ETHEN = 1).
 *
 * Input:           Address of the PHY register to read from.
 *
 * Output:          16 bits of data read from the PHY register.
 *
 * Side Effects:    None
 *
 * Overview:        ReadPHYReg performs an MII read operation.  While in 
 *                  progress, it simply polls the MII BUSY bit wasting time 
 *                  (10.24us).
 *
 * Note:            None
 *****************************************************************************/
PHYREG ReadPHYReg(BYTE Register)
{
    PHYREG Result;

    // Set the right address and start the register read operation
    MIREGADR = Register; Nop();
    MICMD = MICMD_MIIRD; Nop();

    // Loop to wait until the PHY register has been read through the MII
    // This requires 10.24us
    while(MISTATbits.BUSY);

    // Stop reading
    MICMD = 0x00; Nop();
    
    // Obtain results and return
    Result.VAL.v[0] = MIRDL;
    Nop();
    Result.VAL.v[1] = MIRDH;

    return Result;
}//end ReadPHYReg


/******************************************************************************
 * Function:        WritePHYReg
 *
 * PreCondition:    Ethernet module must be enabled (ECON1.ETHEN = 1).
 *
 * Input:           Address of the PHY register to write to.
 *                  16 bits of data to write to PHY register.
 *
 * Output:          None
 *
 * Side Effects:    None
 *
 * Overview:        WritePHYReg performs an MII write operation.  While in 
 *                  progress, it simply polls the MII BUSY bit wasting time 
 *                  (10.24us).
 *
 * Note:            None
 *****************************************************************************/
void WritePHYReg(BYTE Register, WORD Data)
{
    BYTE GIESave;

    // Write the register address
    MIREGADR = Register;

    // Write the data through the MIIM interface
    // Order is important: write low byte first, high byte last
    //
    // Due to a silicon problem, you cannot access any register with LSb address 
    // bits of 0x16 between your write to MIWRL and MIWRH or else the value in 
    // MIWRL will be corrupted.  This inline assembly prevents this by copying 
    // the value to PRODH:PRODL first, which is at fixed locations of 
    // 0xFF4:0xFF3.  These addresses have LSb address bits of 0x14 and 0x13.
    // Interrupts must be disabled to prevent arbitrary ISR code from accessing
    // memory with LSb bits of 0x16 and corrupting the MIWRL value.
    PRODL = ((WORD_VAL*)&Data)->v[0];
    PRODH = ((WORD_VAL*)&Data)->v[1];
    GIESave = INTCON & 0xC0;        // Save GIEH and GIEL bits
    INTCON &= 0x3F;                 // Clear INTCONbits.GIEH and INTCONbits.GIEL
    #if defined(HI_TECH_C)
        asm("movff  _PRODL, _MIWRL");
        asm("nop");
        asm("movff  _PRODH, _MIWRH");
    #else
        _asm
        movff   PRODL, MIWRL
        nop
        movff   PRODH, MIWRH
        _endasm
    #endif
    INTCON |= GIESave;              // Restore GIEH and GIEL value

    // Wait until the PHY register has been written
    // This operation requires 10.24us
    while(MISTATbits.BUSY);
}//end WritePHYReg


/******************************************************************************
 * Function:        void MACPowerDown(void)
 *
 * PreCondition:    None
 *
 * Input:           None
 *
 * Output:          None
 *
 * Side Effects:    None
 *
 * Overview:        MACPowerDown disables the Ethernet module.
 *                  All MAC and PHY registers should not be accessed.
 *
 * Note:            Normally, this function would be called before putting the 
 *                  PIC to sleep.  If a packet is being transmitted while this 
 *                  function is called, this function will block until it is 
 *                  it complete. If anything is being received, it will be 
 *                  completed.
 *                  
 *                  The Ethernet module will continue to draw significant 
 *                  power in sleep mode if this function is not called first.
 *****************************************************************************/
void MACPowerDown(void)
{
    // Disable packet reception
    ECON1bits.RXEN = 0;

    // Make sure any last packet which was in-progress when RXEN was cleared 
    // is completed
    while(ESTATbits.RXBUSY);

    // If a packet is being transmitted, wait for it to finish
    while(ECON1bits.TXRTS);
    
    // Disable the Ethernet module
    ECON2bits.ETHEN = 0;

    // Switch off LEDs.
    LATAbits.LATA0 = 0;
    LATAbits.LATA1 = 0;

}//end MACPowerDown

/******************************************************************************
 * Function:        void MACPowerUp(void)
 *
 * PreCondition:    None
 *
 * Input:           None
 *
 * Output:          None
 *
 * Side Effects:    None
 *
 * Overview:        MACPowerUp returns the Ethernet module back to normal operation
 *                  after a previous call to MACPowerDown().  Calling this 
 *                  function when already powered up will have no effect.
 *
 * Note:            If a link partner is present, it will take 10s of 
 *                  milliseconds before a new link will be established after
 *                  waking up.  While not linked, packets which are 
 *                  transmitted will most likely be lost.  MACIsLinked() can 
 *                  be called to determine if a link is established.
 *****************************************************************************/
void MACPowerUp(void)
{   
    // Power up the Ethernet module
    ECON2bits.ETHEN = 1;

    // Wait for PHY to become ready
    while(!ESTATbits.PHYRDY)

    // Enable packet reception
    ECON1bits.RXEN = 1;
}//end MACPowerUp



/******************************************************************************
 * Function:        void SetRXHashTableEntry(MAC_ADDR DestMACAddr)
 *
 * PreCondition:    SPI bus must be initialized (done in MACInit()).
 *
 * Input:           DestMACAddr: 6 byte group destination MAC address to allow 
 *                               through the Hash Table Filter
 *
 * Output:          Sets the appropriate bit in the EHT* registers to allow 
 *                  packets sent to DestMACAddr to be received if the Hash 
 *                  Table receive filter is enabled
 *
 * Side Effects:    None
 *
 * Overview:        Calculates a CRC-32 using polynomial 0x4C11DB7 and then, 
 *                  using bits 28:23 of the CRC, sets the appropriate bit in 
 *                  the EHT* registers
 *
 * Note:            This code is commented out to save code space on systems 
 *                  that do not need this function.  Change the "#if 0" line 
 *                  to "#if 1" to uncomment it.
 *****************************************************************************/
#if 0
void SetRXHashTableEntry(MAC_ADDR DestMACAddr)
{
    DWORD_VAL CRC = {0xFFFFFFFF};
    BYTE *HTRegister;
    BYTE i, j;

    // Calculate a CRC-32 over the 6 byte MAC address 
    // using polynomial 0x4C11DB7
    for(i = 0; i < sizeof(MAC_ADDR); i++)
    {
        BYTE  crcnext;
    
        // shift in 8 bits
        for(j = 0; j < 8; j++)
        {
            crcnext = 0;
            if(((BYTE_VAL*)&(CRC.v[3]))->bits.b7)
                crcnext = 1;
            crcnext ^= (((BYTE_VAL*)&DestMACAddr.v[i])->bits.b0);
    
            CRC.Val <<= 1;
            if(crcnext)
                CRC.Val ^= 0x4C11DB7;
            // next bit
            DestMACAddr.v[i] >>= 1;
        }
    }
    
    // CRC-32 calculated, now extract bits 28:23
    // Bits 25:23 define where within the Hash Table byte the bit needs to be set
    // Bits 28:26 define which of the 8 Hash Table bytes that bits 25:23 apply to
    i = CRC.v[3] & 0x1F;
    HTRegister = (i >> 2) + &EHT0;
    i = (i << 1) & 0x06;
    ((BYTE_VAL*)&i)->bits.b0 = ((BYTE_VAL*)&CRC.v[2])->bits.b7;
    
    // Set the proper bit in the Hash Table
    *HTRegister |= 1<<i;
}
#endif

---