uint16_t W5100Class::send_data_part_begin(SOCKET s)  // returns 'ptr' to be passed to 'send_data_part' and 'send_data_part_end'
{
  return readSnTX_WR(s);
}

void W5100Class::send_data_part(SOCKET s, uint8_t *data, uint16_t len, uint16_t & ptr)
{
  uint16_t offset = ptr & SMASK;
  uint16_t dstAddr = offset + SBASE[s];

  if (offset + len > SSIZE) 
  {
    // Wrap around circular buffer
    uint16_t size = SSIZE - offset;
    write(dstAddr, data, size);
    write(SBASE[s], data + size, len - size);
  } 
  else {
    write(dstAddr, data, len);
  }

  ptr += len;
}

void W5100Class::send_data_part_end(SOCKET s, uint16_t ptr)
{
  writeSnTX_WR(s, ptr);
}

uint16_t W5100Class::recv_data_part_begin(SOCKET s)  // returns ptr (use getRXReceivedSize for size)
{
  return readSnRX_RD(s);
}

void W5100Class::recv_data_part(SOCKET s, uint8_t *data, uint16_t len, uint16_t & ptr)
{
  read_data(s, (uint8_t *)ptr, data, len);
  ptr += len;
}

void W5100Class::recv_data_part_end(SOCKET s, uint16_t ptr)
{
  writeSnRX_RD(s, ptr);
}