MCA(9) | Kernel Developer's Manual | MCA(9)

# NAME

`MCA`, `mca_intr_establish`, `mca_intr_disestablish`, `mca_intr_evcnt`, `mca_conf_read`, `mca_conf_write` —
MicroChannel Architecture bus

# SYNOPSIS

`#include <sys/bus.h>`
`#include <dev/mca/mcavar.h>`
`#include <dev/mca/mcadevs.h>`

void *
`mca_intr_establish`(mca_chipset_tag_t mc, mca_intr_handle_t hdl, int level, int (*handler)(void *), void *arg);

void
`mca_intr_disestablish`(mca_chipset_tag_t mc, mca_intr_handle_t hdl);

const struct evcnt *
`mca_intr_evcnt`(mca_chipset_tag_t mc, mca_intr_handle_t hdl);

int
`mca_conf_read`(mca_chipset_tag_t mc, int slot, int reg);

void
`mca_conf_write`(mca_chipset_tag_t mc, int slot, int reg, int data);

# DESCRIPTION

The `MCA` device provides support for IBM's MicroChannel Architecture bus found on IBM PS/2 systems and selected workstations. It was designed as a replacement bus for the ISA bus found on IBM's older machines. However, the bus specifications were only available under license, so MCA did not achieve widespread acceptance in the industry.

Being a replacement for the ISA bus, the MCA bus does share some similar aspects with the ISA bus. Some MCA devices can be detected via the usual ISA-style probing. However, most device detection is done through the Programmable Option Select (POS) registers. These registers provide a window into a device to determine device-specific properties and configuration. The configuration of devices and their POS registers is performed using IBM's system configuration software.

The MCA bus uses level-triggered interrupts while the ISA bus uses edge-triggered interrupts. Level triggered interrupts have the advantage that they can be shared among multiple device. Therefore, most MCA-specific devices should be coded with shared interrupts in mind.

# DATA TYPES

Drivers for devices attached to the MCA bus will make use of the following data types:

mca_chipset_tag_t
  Chipset tag for the MCA bus.
mca_intr_handle_t
  The opaque handle describing an established interrupt handler.
struct mca_attach_args
  A structure use to inform the driver of MCA bus properties. It contains the following members:

      	bus_space_tag_t ma_iot;		/* MCA I/O space tag */
      	bus_space_tag_t ma_memt;	/* MCA mem space tag */
      	bus_dma_tag_t ma_dmat;		/* MCA DMA tag */
      	int ma_slot;			/* MCA slot number */
      	int ma_pos[8];			/* MCA POS values */
      	int ma_id;			/* MCA device */

# FUNCTIONS

`mca_intr_establish`(mc, hdl, level, handler, arg)
  Establish a MCA interrupt handler on the MCA bus specified by mc for the interrupt described completely by hdl. The priority of the interrupt is specified by level. When the interrupt occurs the function handler is called with argument arg.
`mca_intr_disestablish`(mc, hdl)
  Dis-establish the interrupt handler on the MCA bus specified by mc for the interrupt described completely hdl.
`mca_intr_evcnt`(mc, hdl)
  Do interrupt event counting on the MCA bus specified by mc for the event described completely by hdl.
`mca_conf_read`(mc, slot, reg)
  Read the POS register reg for the device in slot slot on the MCA bus specified by mc.
`mca_conf_write`(mc, slot, reg, data)
  Write data data to the POS register reg for the device in slot slot on the MCA bus specified by mc.

# AUTOCONFIGURATION

The MCA bus is a direct-connection bus. During autoconfiguration, the parent specifies the MCA device ID for the found device in the ma_id member of the mca_attach_args structure. Drivers should match on the device ID. Device capabilities and configuration information should be read from device POS registers using `mca_conf_read`(). Some important configuration information found in the POS registers include the I/O base address, memory base address and interrupt number. The location of these configurable options with the POS registers are device specific.

# DMA SUPPORT

The MCA bus supports 32-bit, bidirectional DMA transfers. Currently, no machine-independent support for MCA DMA is available.

# CODE REFERENCES

The MCA subsystem itself is implemented within the file sys/dev/mca/mca_subr.c. Machine-dependent portions can be found in sys/arch/<arch>/mca/mca_machdep.c. The database of known devices exists within the file sys/dev/mca/mcadevs_data.h and is generated automatically from the file sys/dev/mca/mcadevs. New vendor and product identifiers should be added to this file. The database can be regenerated using the Makefile sys/dev/mca/Makefile.mcadevs.

A good source of information about MCA devices is IBM's system configuration disk. The disk contains .adf files which describe the location of device configuration options in the POS registers.

# SEE ALSO

mca(4), autoconf(9), bus_dma(9), bus_space(9), driver(9), isa(9)

# BUGS

The machine-independent `MCA` driver does not currently support DMA. MCA devices which require DMA operation currently access the DMA capabilities directly.

October 7, 2001 | NetBSD 9.2