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/*--------------------------------------------------------------------

 * TITLE: Plasma Ethernet MAC

 * AUTHOR: Steve Rhoads (rhoadss@yahoo.com)

 * DATE CREATED: 1/12/08

 * FILENAME: ethernet.c

 * PROJECT: Plasma CPU core

 * COPYRIGHT: Software placed into the public domain by the author.

 *    Software 'as is' without warranty.  Author liable for nothing.

 * DESCRIPTION:

 *    Ethernet MAC implementation.

 *    Data is received from the Ethernet PHY four bits at a time.

 *    After 32-bits are received they are written to 0x13ff0000 + N.

 *    The data is received LSB first for each byte which requires the

 *    nibbles to be swapped.

 *    Transmit data is read from 0x13fe0000.  Write length/4+1 to

 *    ETHERNET_REG to start transfer.

 *--------------------------------------------------------------------*/

#include "plasma.h"

#include "rtos.h"

#include "tcpip.h"

#define POLYNOMIAL  0x04C11DB7   //CRC bit 33 is truncated

#define TOPBIT      (1<<31)

#define BYTE_EMPTY  0xde         //Data copied into receive buffer

#define COUNT_EMPTY 16           //Count to decide there isn't data

#define INDEX_MASK  0xffff       //Size of receive buffer

//void dump(const unsigned char *data, int length);

static unsigned char gDestMac[]={0x5d, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff};

static unsigned int CrcTable[256];

static unsigned char reflect[256];

static unsigned char reflectNibble[256];

static OS_Semaphore_t *SemEthernet, *SemEthTransmit;

static int gIndex;          //byte index into 0x13ff0000 receive buffer

static int gCheckedBefore;

//Read received data from 0x13ff0000.  Data starts with 0x5d+MACaddress.

//Data is being received while processing the data.  Therefore,

//all errors require waiting and then re-processing the data

//to see if the error is fixed by receiving the rest of the packet.

int EthernetReceive(unsigned char *buffer, int length)

{

   int count;

   int start, i, j, shift, offset, index;

   int byte, byteNext;

   unsigned long crc;

   int byteCrc;

   volatile unsigned char *buf = (unsigned char*)ETHERNET_RECEIVE;

   int packetExpected;

   //Find the start of a frame

   packetExpected = MemoryRead(IRQ_STATUS) & IRQ_ETHERNET_RECEIVE;

   MemoryRead(ETHERNET_REG);        //clear receive interrupt

   //Find dest MAC address

   for(offset = 0; offset <= INDEX_MASK; ++offset)

   {

      index = (gIndex + offset) & INDEX_MASK;

      byte = buf[index];

      if(byte == 0x5d)  //bit pattern 01011101

      {

         for(i = 1; i < sizeof(gDestMac); ++i)

         {

            j = (index + i) & INDEX_MASK;

            byte = buf[j];

            if(byte != 0xff && byte != gDestMac[i])

               break;

         }

         if(i == sizeof(gDestMac))

            break;    //found dest MAC

      }

      else if(byte == BYTE_EMPTY && packetExpected == 0)

         return 0;

   }

   if(offset > INDEX_MASK)

      return 0;

   while(gIndex != index)

   {

      buf[gIndex] = BYTE_EMPTY;

      gIndex = (gIndex + 1) & INDEX_MASK;

   }

   //Found start of frame.  Now find end of frame and check CRC.

   start = gIndex;

   gIndex = (gIndex + 1) & INDEX_MASK;           //skip 0x5d byte

   crc = 0xffffffff;

   for(count = 0; count < length; )

   {

      byte = buf[gIndex];

      gIndex = (gIndex + 1) & INDEX_MASK;

      byte = ((byte << 4) & 0xf0) | (byte >> 4); //swap nibbles

      buffer[count++] = (unsigned char)byte;

      byte = reflect[byte] ^ (crc >> 24);        //calculate CRC32

      crc = CrcTable[byte] ^ (crc << 8);

      if(count >= 40)

      {

         //Check if CRC matches to detect end of frame

         byteCrc = reflectNibble[crc >> 24];

         byteNext = buf[gIndex];

         if(byteCrc == byteNext)

         {

            for(i = 1; i < 4; ++i)

            {

               shift = 24 - (i << 3);

               byteCrc = reflectNibble[(crc >> shift) & 0xff];

               byteNext = buf[(gIndex + i) & 0xffff];

               if(byteCrc != byteNext)

               {

                  //printf("nope %d %d 0x%x 0x%x\n", count, i, byteCrc, byteNext);

                  i = 99;

               }

            }

            if(i == 4)

            {

               //Found end of frame -- set used bytes to BYTE_EMPTY

               //printf("Found it! %d\n", count);

               gIndex = (gIndex + 4) & INDEX_MASK;

               for(i = 0; i < count+5; ++i)

                  buf[(start + i) & INDEX_MASK] = BYTE_EMPTY;

               while(gIndex & 3)

               {

                  buf[gIndex] = BYTE_EMPTY;

                  gIndex = (gIndex + 1) & INDEX_MASK;

               }

               gCheckedBefore = 0;

               return count;

            }

         }

      }

   }

   gIndex = start;

   if(gCheckedBefore++ > 1)

   {

      buf[gIndex] = BYTE_EMPTY;

      gIndex = (gIndex + 1) & INDEX_MASK;

   }

   return 0;        //wait for more data

}

//Copy transmit data to 0x13fe0000 with preamble and CRC32

void EthernetTransmit(unsigned char *buffer, int length)

{

   int i, byte, shift;

   unsigned long crc;

   volatile unsigned char *buf = (unsigned char*)ETHERNET_TRANSMIT;

   OS_SemaphorePend(SemEthTransmit, OS_WAIT_FOREVER);

   //Wait for previous transfer to complete

   for(i = 0; i < 10000; ++i)

   {

      if(MemoryRead(IRQ_STATUS) & IRQ_ETHERNET_TRANSMIT)

         break;

   }

   //if(i > 100)

   //   printf("wait=%d ", i);

   Led(2, 2);

   while(length < 60 || (length & 3) != 0)

      buffer[length++] = 0;

   //Start of Ethernet frame

   for(i = 0; i < 7; ++i)

      buf[i] = 0x55;

   buf[7] = 0x5d;

   //Calculate CRC32

   crc = 0xffffffff;

   for(i = 0; i < length; ++i)

   {

      byte = buffer[i];

      buf[i + 8] = (unsigned char)((byte << 4) | (byte >> 4)); //swap nibbles

      byte = reflect[byte] ^ (crc >> 24);        //calculate CRC32

      crc = CrcTable[byte] ^ (crc << 8);

   }

   //Output CRC32

   for(i = 0; i < 4; ++i)

   {

      shift = 24 - (i << 3);

      byte = reflectNibble[(crc >> shift) & 0xff];

      buf[length + 8 + i] = (unsigned char)byte;

   }

   //Start transfer

   length = (length + 12 + 4) >> 2;

   MemoryWrite(ETHERNET_REG, length);

   Led(2, 0);

   OS_SemaphorePost(SemEthTransmit);

}

void EthernetThread(void *arg)

{

   int length;

   int rc;

   unsigned int ticks, ticksLast=0;

   int ticksWait=50;

   IPFrame *ethFrame=NULL;

   (void)arg;

   for(;;)

   {

      OS_InterruptMaskSet(IRQ_ETHERNET_RECEIVE);      //enable interrupt

      rc = OS_SemaphorePend(SemEthernet, ticksWait);  //wait for interrupt

      if(rc)

         ticksWait = 50;

      else

         ticksWait = 2;

      //Process all received packets

      for(;;)

      {

         if(ethFrame == NULL)

            ethFrame = IPFrameGet(FRAME_COUNT_RCV);

         if(ethFrame == NULL)

            break;

         length = EthernetReceive(ethFrame->packet, PACKET_SIZE);

         if(length == 0)

            break;

         Led(1, 1);

         rc = IPProcessEthernetPacket(ethFrame, length);

         Led(1, 0);

         if(rc)

            ethFrame = NULL;

      }

      ticks = OS_ThreadTime();

      if(ticks - ticksLast >= 50)

      {

         IPTick();

         ticksLast = ticks;

      }

   }

}

void EthernetIsr(void *arg)

{

   (void)arg;

   OS_InterruptMaskClear(IRQ_ETHERNET_RECEIVE);

   OS_SemaphorePost(SemEthernet);

}

/******************* CRC32 calculations **********************

 * The CRC32 code is modified from Michale Barr's article in

 * Embedded Systems Programming January 2000.

 * A CRC is really modulo-2 binary division.  Substraction means XOR. */

static unsigned int Reflect(unsigned int value, int bits)

{

   unsigned int num=0;

   int i;

   for(i = 0; i < bits; ++i)

   {

      num = (num << 1) | (value & 1);

      value >>= 1;

   }

   return num;

}

static void CrcInit(void)

{

   unsigned int remainder;

   int dividend, bit, i;

   //Compute the remainder of each possible dividend

   for(dividend = 0; dividend < 256; ++dividend)

   {

      //Start with the dividend followed by zeros

      remainder = dividend << 24;

      //Perform modulo-2 division, a bit at a time

      for(bit = 8; bit > 0; --bit)

      {

         //Try to divide the current data bit

         if(remainder & TOPBIT)

            remainder = (remainder << 1) ^ POLYNOMIAL;

         else

            remainder = remainder << 1;

      }

      CrcTable[dividend] = remainder;

   }

   for(i = 0; i < 256; ++i)

   {

      reflect[i] = (unsigned char)Reflect(i, 8);

      reflectNibble[i] = (unsigned char)((Reflect((i >> 4) ^ 0xf, 4) << 4) |

         Reflect(i ^ 0xf, 4));

   }

}

static void SpinWait(int clocks)

{

   int value = *(volatile int*)COUNTER_REG + clocks;

   while(*(volatile int*)COUNTER_REG - value < 0)

      ;

}

void EthernetInit(unsigned char MacAddress[6])

{

   //Format of SMI data: 0101 A4:A0 R4:R0 00 D15:D0

   unsigned long data=0x5f800100; //SMI R0 = 10Mbps full duplex

   //unsigned long data=0x5f800000; //SMI R0 = 10Mbps half duplex

   int i, value;

   volatile unsigned char *buf = (unsigned char*)ETHERNET_RECEIVE;

   CrcInit();

   if(MacAddress)

   {

      for(i = 0; i < 6; ++i)

      {

         value = MacAddress[i];

         gDestMac[i+1] = (unsigned char)((value >> 4) | (value << 4));

      }

   }

   //Configure Ethernet PHY for 10Mbps full duplex via SMI interface

   MemoryWrite(GPIO0_OUT, ETHERNET_MDIO | ETHERNET_MDIO_WE | ETHERENT_MDC);

   for(i = 0; i < 34; ++i)

   {

      MemoryWrite(GPIO0_OUT, ETHERENT_MDC);    //clock high

      SpinWait(10);

      MemoryWrite(GPIO0_CLEAR, ETHERENT_MDC);  //clock low

      SpinWait(10);

   }

   for(i = 31; i >= 0; --i)

   {

      value = (data >> i) & 1;

      if(value)

         MemoryWrite(GPIO0_OUT, ETHERNET_MDIO);

      else

         MemoryWrite(GPIO0_CLEAR, ETHERNET_MDIO);

      MemoryWrite(GPIO0_OUT, ETHERENT_MDC);    //clock high

      SpinWait(10);

      MemoryWrite(GPIO0_CLEAR, ETHERENT_MDC);  //clock low

      SpinWait(10);

   }

   MemoryWrite(GPIO0_CLEAR, ETHERNET_MDIO_WE | ETHERNET_ENABLE);

   //Clear receive buffer

   for(i = 0; i <= INDEX_MASK; ++i)

      buf[i] = BYTE_EMPTY;

   if(SemEthernet == NULL)

   {

      SemEthernet = OS_SemaphoreCreate("eth", 0);

      SemEthTransmit = OS_SemaphoreCreate("ethT", 1);

      OS_ThreadCreate("eth", EthernetThread, NULL, 240, 0);

   }

   //Setup interrupts for receiving data

   OS_InterruptRegister(IRQ_ETHERNET_RECEIVE, EthernetIsr);

   //Start receive DMA

   MemoryWrite(GPIO0_OUT, ETHERNET_ENABLE);

}