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ISA(9) NetBSD Kernel Developer's Manual ISA(9)
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Maintained for NetBSD
by Kimmo Suominen.
Based on man-cgi by Panagiotis Christias.
ISA, isa_intr_alloc, isa_intr_establish, isa_intr_disestablish,
isa_intr_evcnt, isa_dmamap_create, isa_dmamap_destroy, isa_dmamem_alloc,
isa_dmamem_free, isa_dmamem_map, isa_dmamem_unmap, isa_malloc, isa_free,
isa_dmastart, isa_dmaabort, isa_dmacount, isa_dmadone, isa_dmamaxsize,
isa_drq_alloc, isa_drq_free, isa_drq_isfree, isa_dmacascade, isa_mappage
-- Industry-standard Architecture
isa_intr_alloc(isa_chipset_tag_t ic, int mask, int type, int *irq);
const struct evcnt *
isa_intr_evcnt(isa_chipset_tag_t ic, int irq);
isa_intr_establish(isa_chipset_tag_t ic, int irq, int type, int level,
int (*handler)(void *), void *arg);
isa_intr_disestablish(isa_chipset_tag_t ic, void *ih);
isa_dmamap_create(isa_chipset_tag_t ic, int chan, bus_size_t size,
isa_dmamap_destroy(isa_chipset_tag_t ic, int chan);
isa_dmamem_alloc(isa_chipset_tag_t ic, int chan, bus_size_t size,
bus_addr_t *addrp, int flags);
isa_dmamem_free(isa_chipset_tag_t ic, int chan, bus_addr_t addr,
isa_dmamem_map(isa_chipset_tag_t ic, int chan, bus_addr_t addr,
bus_size_t size, void **kvap, int flags);
isa_dmamem_unmap(isa_chipset_tag_t ic, int chan, void *kva, size_t size);
isa_malloc(isa_chipset_tag_t ic, int chan, size_t size, int pool,
isa_free(void *addrp, int pool);
isa_dmastart(isa_chipset_tag_t ic, int chan, bus_addr_t addr,
bus_size_t size, struct lwp *lwp, int flags, int bf);
isa_dmaabort(isa_chipset_tag_t ic, int chan);
isa_dmacount(isa_chipset_tag_t ic, int chan);
isa_dmadone(isa_chipset_tag_t ic, int chan);
isa_dmamaxsize(isa_chipset_tag_t ic, int chan);
isa_drq_alloc(isa_chipset_tag_t ic, int chan);
isa_drq_free(isa_chipset_tag_t ic, int chan);
isa_drq_isfree(isa_chipset_tag_t ic, int chan);
isa_dmacascade(isa_chipset_tag_t ic, int chan);
isa_mappage(void *mem, off_t offset, int prot);
The machine-independent ISA subsystem provides support for the ISA bus.
The ISA bus was introduced on the IBM PC/AT. It is an extension to the
original bus found on the original IBM PC. The ISA bus is essentially
the host bus of the Intel 80286 processor, however the widespread accep-
tance of the bus as a de facto standard has seen it appear on systems
without Intel processors.
The ISA bus has a 16-bit data bus, a 24-bit memory address bus, a 16-bit
I/O address bus, and operates at 8MHz. It provides 15 interrupt lines
and 8 DMA channels supporting DMA transfers of 64KB or 128KB transfers
depending on the width of the channel being used. Historically, some
devices only decoded the 10 lowest bits of the I/O address bus, prevent-
ing use of the full 16-bit address space.
On newer machines, the ISA bus is no longer connected directly to the
host bus, and is usually connected via a PCI-ISA bridge. Either way, the
bus looks the same to the device driver.
Drivers for devices attached to the ISA bus will make use of the follow-
ing data types:
Chipset tag for the ISA bus.
Location hints for devices are recorded in this structure. It
contains the following members:
bus_space_tag_t ia_iot; /* isa i/o space tag */
bus_space_tag_t ia_memt; /* isa mem space tag */
bus_dma_tag_t ia_dmat; /* DMA tag */
int ia_iobase; /* base i/o address */
int ia_iosize; /* span of ports used */
int ia_maddr; /* physical mem addr */
u_int ia_msize; /* size of memory */
int ia_irq; /* interrupt request */
int ia_drq; /* DMA request */
int ia_drq2; /* second DMA request */
void *ia_aux; /* driver specific */
isa_intr_alloc(ic, mask, type, irq)
This function is generally not required by device drivers. It
is used by bridges attaching other busses to the ISA bus.
Returns the event counter associated with interrupt line irq.
isa_intr_establish(ic, irq, type, level, handler, arg)
To establish an ISA interrupt handler, a driver calls
isa_intr_establish() with the interrupt number irq, type type,
and level level. When the interrupt occurs the function handler
is called with argument arg. Valid values for type are:
Reserve interrupt, but don't actually establish.
isa_intr_establish() returns an opaque handle to an event
descriptor if it succeeds, and returns NULL on failure.
Dis-establish the interrupt handler with handle ih. The handle
was returned from isa_intr_establish().
Reserves the DMA channel chan for future use. Normally, this
call precedes an isa_dmamap_create() call. It is an error to
start DMA on a channel that has not been reserved with
Marks the DMA channel chan as available again.
isa_dmamap_create(ic, chan, size, flags)
Creates a DMA map for channel chan. It is initialised to accept
maximum DMA transfers of size size. Valid values for the flags
argument are the same as for bus_dmamap_create() (see
bus_dma(9)). This function returns zero on success or an error
value on failure.
Destroy the DMA map for DMA channel chan.
isa_dmamem_alloc(ic, chan, size, addrp, flags)
Allocate DMA-safe memory of size size for channel chan. Valid
values for the flags argument are the same as for
bus_dmamem_alloc() (see bus_dma(9)). The bus-address of the
memory is returned in addrp. This function returns zero on suc-
cess or an error value on failure.
isa_dmamem_free(ic, chan, addr, size)
Frees memory previously allocated by isa_dmamem_alloc() for
channel chan. The bus-address and size of the memory are speci-
fied by addr and size respectively.
isa_dmamem_map(ic, chan, addr, size, kvap, flags)
Maps DMA-safe memory (allocated with isa_dmamem_alloc()) speci-
fied by bus-address addr and of size size into kernel virtual
address space for DMA channel chan. Valid values for the flags
argument are the same as for bus_dmamem_map() (see bus_dma(9)).
The kernel virtual address is returned in kvap. This function
returns zero on success or an error value on failure.
isa_dmamem_unmap(ic, chan, kva, size)
Unmaps memory (previously mapped with isa_dmamem_map()) of size
size for channel chan. The kernel virtual address space used by
the mapping is freed.
isa_malloc(ic, chan, size, pool, flags)
This function is a shortcut for allocating and mapping DMA-safe
memory in a single step. The arguments correspond with the
arguments to isa_dmamem_alloc() and isa_dmamem_map(). The argu-
ment pool is a pool to record the memory allocation. This func-
tion returns a pointer to the DMA-safe memory.
This function is a shortcut for unmapping and deallocating DMA-
safe memory in a single step. It replaces isa_dmamem_unmap()
and isa_dmamem_free(). The argument addrp is the pointer to the
DMA-safe memory returned by isa_malloc(). The argument pool is
the same as the value passed to isa_malloc().
isa_dmastart(ic, chan, addr, size, lwp, flags, bf)
Load DMA memory specified by address addr of size size into the
DMA controller at channel chan and set it in motion. The argu-
ment lwp is used to indicate the address space in which the
buffer is located. If NULL, the buffer is assumed to be in ker-
nel space. Otherwise, the buffer is assumed to be in lwp lwp 's
address space. The argument flags describes the type of ISA
DMA. Valid values are:
DMA transfer from host to device.
DMA transfer to host from device.
Transfer buffer once and stop.
Transfer buffer continuously in loop until notified to
Transfer buffer continuously in loop and demand mode.
The argument bf is the bus-space flags. Valid values are the
same as for bus_dmamap_load() (see bus_dma(9)).
Abort a DMA transfer on channel chan.
Returns the offset in the DMA memory of the current DMA transfer
on channel chan.
Unloads the DMA memory on channel chan after a DMA transfer has
Returns the maximum allowable DMA transfer size for channel
If the ia_drq or ia_drq2 members of struct isa_attach_args are
wildcarded, then the driver is expected to probe the hardware
for valid DMA channels. In this case, the driver can check to
see if the hardware-supported DMA channel chan is available for
Programs the 8237 DMA controller channel chan to accept external
DMA control by the device hardware.
isa_mappage(mem, offset, prot)
Provides support for user mmap(2)'ing of DMA-safe memory.
The ISA bus is an indirect-connection bus. During autoconfiguration each
driver is required to probe the bus for the presence of a device. An ISA
driver will receive a pointer to struct isa_attach_args hinting at "loca-
tions" on the ISA bus where the device may be located. They should use
the ia_iobase, ia_iosize, ia_maddr, and ia_msize members. Not all of
these hints will be necessary; locators may be wildcarded with IOBASEUNK
and MADDRUNK for ia_iobase and ia_maddr respectively. If a driver can
probe the device for configuration information at default locations, it
may update the members of struct isa_attach_args. The IRQ and DMA loca-
tors can also be wildcarded with IRQUNK and DRQUNK respectively.
During the driver attach step, the I/O and memory address spaces should
be mapped (see bus_space(9)).
Extensive DMA facilities are provided for the ISA bus. A driver can use
up to two DMA channels simultaneously. The DMA channels allocated during
autoconfiguration are passed to the driver during the driver attach using
the ia_drq and ia_drq2 members of struct isa_attach_args.
Before allocating resources for DMA transfers on the ISA bus, a driver
should check the maximum allowable DMA transfer size for the DMA channel
A DMA map should be created first using isa_dmamap_create(). A DMA map
describes how DMA memory is loaded into the DMA controllers. Only DMA-
safe memory can be used for DMA transfers. DMA-safe memory is allocated
using isa_dmamem_alloc(). The memory allocated by isa_dmamem_alloc()
must now be mapped into kernel virtual address space by isa_dmamem_map()
so that it can be accessed by the driver.
For a DMA transfer from the host to the device, the driver will fill the
DMA memory with the data to be transferred. The DMA-transfer of the mem-
ory is started using isa_dmastart() with flags containing DMAMODE_WRITE.
When the DMA transfer is completed, a call to isa_dmadone() cleans up the
DMA transfer by unloading the memory from the controller.
For a DMA transfer from the device to the host, the DMA-transfer is
started using isa_dmastart() with flags containing DMAMODE_READ. When
the DMA transfer is completed, a call to isa_dmadone() cleans up the DMA
transfer by unloading the memory from the controller. The memory can now
be access by the driver.
When the DMA resources are no longer required they should be released
using isa_dmamem_unmap(), isa_dmamem_free() and isa_dmamap_destroy().
The ISA subsystem itself is implemented within the files
sys/dev/isa/isa.c and sys/dev/isa/isadma.c.
isa(4), autoconf(9), bus_dma(9), bus_space(9), driver(9), isapnp(9)
The machine-independent ISA subsystem appeared in NetBSD 1.2.
The previous behaviour of isa_intr_establish() was to invoke panic() on
failure. isa_intr_establish() now returns NULL on failure. Some old
drivers written for the former behaviour discard the return value.
NetBSD 9.99 January 29, 2006 NetBSD 9.99