Constructor

1) Check and increment the device index.

  static int dev;
  ....
  if (dev >= SNDRV_CARDS)
          return -ENODEV;
  if (!enable[dev]) {
          dev++;
          return -ENOENT;
  }
            

At each time probe callback is called, check the availability of the device. If not available, simply increment the device index and returns. dev will be incremented also later (step 7).

2) Create a card instance

  struct snd_card *card;
  ....
  card = snd_card_new(index[dev], id[dev], THIS_MODULE, 0);
            

The detail will be explained in the section Management of Cards and Components.

3) Create a main component

In this part, the PCI resources are allocated.

  struct mychip *chip;
  ....
  if ((err = snd_mychip_create(card, pci, &chip)) < 0) {
          snd_card_free(card);
          return err;
  }
            

4) Set the driver ID and name strings.

  strcpy(card->driver, "My Chip");
  strcpy(card->shortname, "My Own Chip 123");
  sprintf(card->longname, "%s at 0x%lx irq %i",
          card->shortname, chip->ioport, chip->irq);
            

The shortname field is a string shown as more verbose name. The longname field contains the information which is shown in /proc/asound/cards.

5) Create other components, such as mixer, MIDI, etc.

Here you define the basic components such as PCM, mixer (e.g. AC97), MIDI (e.g. MPU-401), and other interfaces. Also, if you want a proc file, define it here, too.

6) Register the card instance.

  if ((err = snd_card_register(card)) < 0) {
          snd_card_free(card);
          return err;
  }
            

Will be explained in the section Management of Cards and Components, too.

7) Set the PCI driver data and return zero.

        pci_set_drvdata(pci, card);
        dev++;
        return 0;