MCA, mca_intr_establish, mca_intr_disestablish, mca_intr_evcnt,
mca_conf_read, mca_conf_write - MicroChannel Architecture bus
mca_intr_establish(mca_chipset_tag_t mc, mca_intr_handle_t hdl,
int level, int (*handler)(void *), void *arg);
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);
mca_conf_read(mca_chipset_tag_t mc, int slot, int reg);
mca_conf_write(mca_chipset_tag_t mc, int slot, int reg, int data);
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 edgetriggered
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.
Drivers for devices attached to the MCA bus will make use of the following
Chipset tag for the MCA bus.
The opaque handle describing an established interrupt handler.
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; /* MCA POS values */
int ma_id; /* MCA device */
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.
Dis-establish the interrupt handler on the MCA bus specified by
mc for the interrupt described completely 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.
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.
The MCA bus supports 32-bit, bidirectional DMA transfers. Currently, no
machine-independent support for MCA DMA is available.
This section describes places within the NetBSD source tree where actual
code implementing or utilising the machine-independent MCA subsystem can
be found. All pathnames are relative to /usr/src.
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
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.
mca(4), autoconf(9), bus_dma(9), bus_space(9), driver(9), isa(9)
The machine-independent MCA driver does not currently support DMA. MCA
devices which require DMA operation currently access the DMA capabilities
BSD October 7, 2001 BSD
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