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Supported flags

• bits 0-3: chipset forced mode(s)

  PPB_COMPATIBLE  0x0     /* Centronics compatible mode */
  PPB_NIBBLE      0x1     /* reverse 4 bit mode */
  PPB_PS2         0x2     /* PS/2 byte mode */
  PPB_EPP         0x4     /* EPP mode, 32 bit */
  PPB_ECP         0x8     /* ECP mode */

  And any mixed values.

• bit 4: EPP protocol (0 EPP 1.9, 1 EPP 1.7)
• bit 5: activate IRQ (1 IRQ disabled, 0 IRQ enabled)
• bit 6: disable chipset specific detection
• bit 7: disable FIFO detection

Supported chipsets

Some parallel port chipsets are explicitly supported: detection and initialisation code has been written according to their datasheets.

• SMC FDC37C665GT and FDC37C666GT chipsets
• Natsemi PC873xx-family (PC87332 and PC87306)
• Winbond W83877xx-family (W83877F and W83877AF)
• SMC-like chipsets with mixed modes (see ppbus(4))

Adding support to a new chipset

You may want to add support for the newest chipset your motherboard was sold with. For the ISA bus, just retrieve the specs of the chipset and write the corresponding ppc_mychipset_detect() function. Then add an entry to the general purpose ppc_detect() function.

Your ppc_mychipset_detect() function should ensure that if the mode field of the flags boot variable is not null, then the operating mode is forced to the given mode and no other mode is available and ppb->ppb_avm field contains the available modes of the chipset.