[xv6 學習紀錄 11-3] E1000 mannual 與其中概念的程式碼實做

void
pci_init()
{
  // we'll place the e1000 registers at this address.
  // vm.c maps this range.
  // 我們會把 e1000 registers 放到這個位置
  // 如下圖，他會被放在 unused and other I/O devices 的區塊
  // vm.c 會負責做這個 mapping
  uint64 e1000_regs = 0x40000000L;

  // qemu -machine virt puts PCIe config space here.
  // vm.c maps this range.
  // 這裡則是在 mapping PCIe config
  // 跟前面一樣，是放在 unused and other I/O devices 的區塊
  // ECAM for Extended Configuration Access Mechanism
  uint32  *ecam = (uint32 *) 0x30000000L;
  
  // look at each possible PCI device on bus 0.
  // bus == 0 是固定的，只掃描 Primary Bus
  // dev: 0 ~ 31 設備號碼，每一個代表一個獨立設備例如 E1000 網卡、顯示卡，現在要尋找 E1000
  // func: 功能號碼，每一個設備可以有多個 function, 這裡只需要尋找第 0 個功能，E1000 也只有一個功能
  // offset: 指向配置空間中特定 4 位元組暫存器的偏移量, 設為 0
  // off: 透過上面的資訊取得總 offset
  for(int dev = 0; dev < 32; dev++){
    int bus = 0;
    int func = 0;
    int offset = 0;
    uint32 off = (bus << 16) | (dev << 11) | (func << 8) | (offset);
    volatile uint32 *base = ecam + off;
    uint32 id = base[0];
    
    // 100e:8086 is an e1000
    if(id == 0x100e8086){
      // command and status register.
      // bit 0 : I/O access enable
      // bit 1 : memory access enable
      // bit 2 : enable mastering
      base[1] = 7;
      __sync_synchronize();

      for(int i = 0; i < 6; i++){
        uint32 old = base[4+i];

        // writing all 1's to the BAR causes it to be
        // replaced with its size.
        base[4+i] = 0xffffffff;
        __sync_synchronize();

        base[4+i] = old;
      }

      // tell the e1000 to reveal its registers at
      // physical address 0x40000000.
      base[4+0] = e1000_regs;

      e1000_init((uint32*)e1000_regs);
    }
  }
}

// called by pci_init().
// xregs is the memory address at which the
// e1000's registers are mapped.
void
e1000_init(uint32 *xregs)
{
  int i;

  initlock(&e1000_lock, "e1000");

  regs = xregs;

  // Reset the device
  regs[E1000_IMS] = 0; // disable interrupts
  regs[E1000_CTL] |= E1000_CTL_RST;
  regs[E1000_IMS] = 0; // redisable interrupts
  __sync_synchronize();

  // [E1000 14.5] Transmit initialization
  memset(tx_ring, 0, sizeof(tx_ring));
  for (i = 0; i < TX_RING_SIZE; i++) {
    tx_ring[i].status = E1000_TXD_STAT_DD;
    tx_mbufs[i] = 0;
  }
  regs[E1000_TDBAL] = (uint64) tx_ring;
  if(sizeof(tx_ring) % 128 != 0)
    panic("e1000");
  regs[E1000_TDLEN] = sizeof(tx_ring);
  regs[E1000_TDH] = regs[E1000_TDT] = 0;
  
  // [E1000 14.4] Receive initialization
  memset(rx_ring, 0, sizeof(rx_ring));
  for (i = 0; i < RX_RING_SIZE; i++) {
    rx_mbufs[i] = mbufalloc(0);
    if (!rx_mbufs[i])
      panic("e1000");
    rx_ring[i].addr = (uint64) rx_mbufs[i]->head;
  }
  regs[E1000_RDBAL] = (uint64) rx_ring;
  if(sizeof(rx_ring) % 128 != 0)
    panic("e1000");
  regs[E1000_RDH] = 0;
  regs[E1000_RDT] = RX_RING_SIZE - 1;
  regs[E1000_RDLEN] = sizeof(rx_ring);

  // filter by qemu's MAC address, 52:54:00:12:34:56
  regs[E1000_RA] = 0x12005452;
  regs[E1000_RA+1] = 0x5634 | (1<<31);
  // multicast table
  for (int i = 0; i < 4096/32; i++)
    regs[E1000_MTA + i] = 0;

  // transmitter control bits.
  regs[E1000_TCTL] = E1000_TCTL_EN |  // enable
    E1000_TCTL_PSP |                  // pad short packets
    (0x10 << E1000_TCTL_CT_SHIFT) |   // collision stuff
    (0x40 << E1000_TCTL_COLD_SHIFT);
  regs[E1000_TIPG] = 10 | (8<<10) | (6<<20); // inter-pkt gap

  // receiver control bits.
  regs[E1000_RCTL] = E1000_RCTL_EN | // enable receiver
    E1000_RCTL_BAM |                 // enable broadcast
    E1000_RCTL_SZ_2048 |             // 2048-byte rx buffers
    E1000_RCTL_SECRC;                // strip CRC
  
  // ask e1000 for receive interrupts.
  regs[E1000_RDTR] = 0; // interrupt after every received packet (no timer)
  regs[E1000_RADV] = 0; // interrupt after every packet (no timer)
  regs[E1000_IMS] = (1 << 7); // RXDW -- Receiver Descriptor Write Back
}