BUS_SPACE(9) FreeBSD Kernel Developer's Manual BUS_SPACE(9)
NAME
bus_space, bus_space_barrier, bus_space_copy_region_1,
bus_space_copy_region_2, bus_space_copy_region_4,
bus_space_copy_region_8, bus_space_free, bus_space_map, bus_space_read_1,
bus_space_read_2, bus_space_read_4, bus_space_read_8,
bus_space_read_multi_1, bus_space_read_multi_2, bus_space_read_multi_4,
bus_space_read_multi_8, bus_space_read_region_1, bus_space_read_region_2,
bus_space_read_region_4, bus_space_read_region_8, bus_space_set_region_1,
bus_space_set_region_2, bus_space_set_region_4, bus_space_set_region_8,
bus_space_subregion, bus_space_unmap, bus_space_write_1,
bus_space_write_2, bus_space_write_4, bus_space_write_8,
bus_space_write_multi_1, bus_space_write_multi_2,
bus_space_write_multi_4, bus_space_write_multi_8,
bus_space_write_region_1, bus_space_write_region_2,
bus_space_write_region_4, bus_space_write_region_8 - bus space manipula-
tion functions
SYNOPSIS
#include <machine/bus.h>
int
bus_space_map(bus_space_tag_t space, bus_addr_t address, bus_size_t size,
int flags, bus_space_handle_t *handlep)
void
bus_space_unmap(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t size)
int
bus_space_subregion(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, bus_size_t size, bus_space_handle_t *nhandlep)
int
bus_space_alloc(bus_space_tag_t space, bus_addr_t reg_start,
bus_addr_t reg_end, bus_size_t size, bus_size_t alignment,
bus_size_t boundary, int flags, bus_addr_t *addrp,
bus_space_handle_t *handlep)
void
bus_space_free(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t size)
u_int8_t
bus_space_read_1(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset)
u_int16_t
bus_space_read_2(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset)
u_int32_t
bus_space_read_4(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset)
u_int64_t
bus_space_read_8(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset)
void
bus_space_write_1(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int8_t value)
void
bus_space_write_2(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int16_t value)
void
bus_space_write_4(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int32_t value)
void
bus_space_write_8(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int64_t value)
void
bus_space_barrier(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, bus_size_t length, int flags)
void
bus_space_read_region_1(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int8_t *datap, bus_size_t count)
void
bus_space_read_region_2(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int16_t *datap, bus_size_t count)
void
bus_space_read_region_4(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int32_t *datap, bus_size_t count)
void
bus_space_read_region_8(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int64_t *datap, bus_size_t count)
void
bus_space_write_region_1(bus_space_tag_t space,
bus_space_handle_t handle, bus_size_t offset, u_int8_t *datap,
bus_size_t count)
void
bus_space_write_region_2(bus_space_tag_t space,
bus_space_handle_t handle, bus_size_t offset, u_int16_t *datap,
bus_size_t count)
void
bus_space_write_region_4(bus_space_tag_t space,
bus_space_handle_t handle, bus_size_t offset, u_int32_t *datap,
bus_size_t count)
void
bus_space_write_region_8(bus_space_tag_t space,
bus_space_handle_t handle, bus_size_t offset, u_int64_t *datap,
bus_size_t count)
void
bus_space_copy_region_1(bus_space_tag_t space,
bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset,
bus_size_t count)
void
bus_space_copy_region_2(bus_space_tag_t space,
bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset,
bus_size_t count)
void
bus_space_copy_region_4(bus_space_tag_t space,
bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset,
bus_size_t count)
void
bus_space_copy_region_8(bus_space_tag_t space,
bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset,
bus_size_t count)
void
bus_space_set_region_1(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int8_t value, bus_size_t count)
void
bus_space_set_region_2(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int16_t value, bus_size_t count)
void
bus_space_set_region_4(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int32_t value, bus_size_t count)
void
bus_space_set_region_8(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int64_t value, bus_size_t count)
void
bus_space_read_multi_1(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int8_t *datap, bus_size_t count)
void
bus_space_read_multi_2(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int16_t *datap, bus_size_t count)
void
bus_space_read_multi_4(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int32_t *datap, bus_size_t count)
void
bus_space_read_multi_8(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int64_t *datap, bus_size_t count)
void
bus_space_write_multi_1(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int8_t *datap, bus_size_t count)
void
bus_space_write_multi_2(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int16_t *datap, bus_size_t count)
void
bus_space_write_multi_4(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int32_t *datap, bus_size_t count)
void
bus_space_write_multi_8(bus_space_tag_t space, bus_space_handle_t handle,
bus_size_t offset, u_int64_t *datap, bus_size_t count)
SYNOPSIS
The bus_space functions exist to allow device drivers machine-independent
access to bus memory and register areas. All of the functions and types
described in this document can be used by including the <machine/bus.h>
header file.
Many common devices are used on multiple architectures, but are accessed
differently on each because of architectural constraints. For instance,
a device which is mapped in one systems's I/O space may be mapped in mem-
ory space on a second system. On a third system, architectural limita-
tions might change the way registers need to be accessed (e.g. creating
a non-linear register space). In some cases, a single driver may need to
access the same type of device in multiple ways in a single system or ar-
chitecture. The goal of the bus_space functions is to allow a single
driver source file to manipulate a set of devices on different system ar-
chitectures, and to allow a single driver object file to manipulate a set
of devices on multiple bus types on a single architecture.
Not all busses have to implement all functions described in this docu-
ment, though that is encouraged if the operations are logically supported
by the bus. Unimplemented functions should cause compile-time errors if
possible.
All of the interface definitions described in this document are shown as
function prototypes and discussed as if they were required to be func-
tions. Implementations are encouraged to implement prototyped (type-
checked) versions of these interfaces, but may implement them as macros
if appropriate. Machine-dependent types, variables, and functions should
be marked clearly in <machine/bus.h> to avoid confusion with the machine-
independent types and functions, and, if possible, should be given names
which make the machine-dependence clear.
CONCEPTS AND GUIDELINES
Bus spaces are described by bus space tags, which can be created only by
machine-dependent code. A given machine may have several different types
of bus space (e.g. memory space and I/O space), and thus may provide mul-
tiple different bus space tags. Individual busses or devices on a ma-
chine may use more than one bus space tag. For instance, ISA devices are
given an ISA memory space tag and an ISA I/O space tag. Architectures
may have several different tags which represent the same type of space,
for instance because of multiple different host bus interface chipsets.
A range in bus space is described by a bus address and a bus size. The
bus address describes the start of the range in bus space. The bus size
describes the size of the range in bytes. Busses which are not byte ad-
dressable may require use of bus space ranges with appropriately aligned
addresses and properly rounded sizes.
Access to regions of bus space is facilitated by use of bus space han-
dles, which are usually created by mapping a specific range of a bus
space. Handles may also be created by allocating and mapping a range of
bus space, the actual location of which is picked by the implementation
within bounds specified by the caller of the allocation function.
All of the bus space access functions require one bus space tag argument,
at least one handle argument, and at least one offset argument (a bus
size). The bus space tag specifies the space, each handle specifies a
region in the space, and each offset specifies the offset into the region
of the actual location(s) to be accessed. Offsets are given in bytes,
though busses may impose alignment constraints. The offset used to ac-
cess data relative to a given handle must be such that all of the data
being accessed is in the mapped region that the handle describes. Trying
to access data outside that region is an error.
Because some architectures' memory systems use buffering to improve memo-
ry and device access performance, there is a mechanism which can be used
to create ``barriers'' in the bus space read and write stream. There are
three types of barriers: read, write, and read/write. All reads started
to the region before a read barrier must complete before any reads after
the read barrier are started. (The analogous requirement is true for
write barriers.) Read/write barriers force all reads and writes started
before the barrier to complete before any reads or writes after the bar-
rier are started. Correctly-written drivers will include all appropriate
barriers, and assume only the read/write ordering imposed by the barrier
operations.
People trying to write portable drivers with the bus_space functions
should try to make minimal assumptions about what the system allows. In
particular, they should expect that the system requires bus space ad-
dresses being accessed to be naturally aligned (i.e. base address of han-
dle added to offset is a multiple of the access size), and that the sys-
tem does alignment checking on pointers (i.e. pointer to objects being
read and written must point to properly-aligned data).
The descriptions of the bus_space functions given below all assume that
they are called with proper arguments. If called with invalid arguments
or arguments that are out of range (e.g. trying to access data outside of
the region mapped when a given handle was created), undefined behaviour
results. In that case, they may cause the system to halt, either inten-
tionally (via panic) or unintentionally (by causing a fatal trap of by
some other means) or may cause improper operation which is not immediate-
ly fatal. Functions which return void or which return data read from bus
space (i.e., functions which don't obviously return an error code) do not
fail. They could only fail if given invalid arguments, and in that case
their behaviour is undefined.
TYPES
Several types are defined in <machine/bus.h> to facilitate use of the
bus_space functions by drivers.
bus_addr_t
The bus_addr_t type is used to describe bus addresses. It must be an un-
signed integral type capable of holding the largest bus address usable by
the architecture. This type is primarily used when mapping and unmapping
bus space.
bus_size_t
The bus_size_t type is used to describe sizes of ranges in bus space. It
must be an unsigned integral type capable of holding the size of the
largest bus address range usable on the architecture. This type is used
by virtually all of the bus_space functions, describing sizes when map-
ping regions and offsets into regions when performing space access opera-
tions.
bus_space_tag_t
The bus_space_tag_t type is used to describe a particular bus space on a
machine. Its contents are machine-dependent and should be considered
opaque by machine-independent code. This type is used by all bus_space
functions to name the space on which they're operating.
bus_space_handle_t
The bus_space_handle_t type is used to describe a mapping of a range of
bus space. Its contents are machine-dependent and should be considered
opaque by machine-independent code. This type is used when performing
bus space access operations.
MAPPING AND UNMAPPING BUS SPACE
Bus space must be mapped before it can be used, and should be unmapped
when it is no longer needed. The bus_space_map() and bus_space_unmap()
functions provide these capabilities.
Some drivers need to be able to pass a subregion of already-mapped bus
space to another driver or module within a driver. The
bus_space_subregion() function allows such subregions to be created.
bus_space_map(space, address, size, flags, handlep)
The bus_space_map() function maps the region of bus space named by the
space, address, and size arguments. If successful, it returns zero and
fills in the bus space handle pointed to by handlep with the handle that
can be used to access the mapped region. If unsuccessful, it will return
non-zero and leave the bus space handle pointed to by handlep in an unde-
fined state.
The flags argument controls how the space is to be mapped. Supported
flags include:
BUS_SPACE_MAP_CACHEABLE Try to map the space so that accesses can
be cached and/or prefetched by the system.
If this flag is not specified, the imple-
mentation should map the space so that it
will not be cached or prefetched.
This flag must have a value of 1 on all
implementations for backward compatibili-
ty.
BUS_SPACE_MAP_LINEAR Try to map the space so that its contents
can be accessed linearly via normal memory
access methods (e.g. pointer dereferencing
and structure accesses). This is useful
when software wants to do direct access to
a memory device, e.g. a frame buffer. If
this flag is specified and linear mapping
is not possible, the bus_space_map() call
should fail. If this flag is not speci-
fied, the system may map the space in
whatever way is most convenient.
Not all combinations of flags make sense or are supported with all
spaces. For instance, BUS_SPACE_MAP_CACHEABLE may be meaningless when
used on many systems' I/O port spaces, and on some systems
BUS_SPACE_MAP_LINEAR without BUS_SPACE_MAP_CACHEABLE may never work. When
the system hardware or firmware provides hints as to how spaces should be
mapped (e.g. the PCI memory mapping registers' "prefetchable" bit), those
hints should be followed for maximum compatibility. On some systems, re-
questing a mapping that cannot be satisfied (e.g. requesting a non-
cacheable mapping when the system can only provide a cacheable one) will
cause the request to fail.
Some implementations may keep track of use of bus space for some or all
bus spaces and refuse to allow duplicate allocations. This is encouraged
for bus spaces which have no notion of slot-specific space addressing,
such as ISA and VME, and for spaces which coexist with those spaces (e.g.
EISA and PCI memory and I/O spaces co-existing with ISA memory and I/O
spaces).
Mapped regions may contain areas for which no there is no device on the
bus. If space in those areas is accessed, the results are bus-dependent.
bus_space_unmap(space, handle, size)
The bus_space_unmap() function unmaps a region of bus space mapped with
bus_space_map(). When unmapping a region, the size specified should be
the same as the size given to bus_space_map() when mapping that region.
After bus_space_unmap() is called on a handle, that handle is no longer
valid. (If copies were made of the handle they are no longer valid, ei-
ther.)
This function will never fail. If it would fail (e.g. because of an ar-
gument error), that indicates a software bug which should cause a panic.
In that case, bus_space_unmap() will never return.
bus_space_subregion(space, handle, offset, size, nhandlep)
The bus_space_subregion() function is a convenience function which makes
a new handle to some subregion of an already-mapped region of bus space.
The subregion described by the new handle starts at byte offset offset
into the region described by handle, with the size give by size, and must
be wholly contained within the original region.
If successful, bus_space_subregion() returns zero and fills in the bus
space handle pointed to by nhandlep. If unsuccessful, it returns non-zero
and leaves the bus space handle pointed to by nhandlep in an undefined
state. In either case, the handle described by handle remains valid and
is unmodified.
When done with a handle created by bus_space_subregion(), the handle
should be thrown away. Under no circumstances should bus_space_unmap()
be used on the handle. Doing so may confuse any resource management be-
ing done on the space, and will result in undefined behaviour. When
bus_space_unmap() or bus_space_free() is called on a handle, all subre-
gions of that handle become invalid.
ALLOCATING AND FREEING BUS SPACE
Some devices require or allow bus space to be allocated by the operating
system for device use. When the devices no longer need the space, the
operating system should free it for use by other devices. The
bus_space_alloc() and bus_space_free() functions provide these capabili-
ties.
bus_space_alloc(space, reg_start, reg_end, size, alignment, boundary,
flags, addrp, handlep)
The bus_space_alloc() function allocates and maps a region of bus space
with the size given by size, corresponding to the given constraints. If
successful, it returns zero, fills in the bus address pointed to by addrp
with the bus space address of the allocated region, and fills in the bus
space handle pointed to by handlep with the handle that can be used to
access that region. If unsuccessful, it returns non-zero and leaves the
bus address pointed to by addrp and the bus space handle pointed to by
handlep in an undefined state.
Constraints on the allocation are given by the reg_start, reg_end,
alignment, and boundary parameters. The allocated region will start at
or after reg_start and end before or at reg_end. The alignment constraint
must be a power of two, and the allocated region will start at an address
that is an even multiple of that power of two. The boundary constraint,
if non-zero, ensures that the region is allocated so that first address
in region / boundary has the same value as last address in region /
boundary. If the constraints cannot be met, bus_space_alloc() will fail.
It is an error to specify a set of constraints that can never be met (for
example, size greater than boundary).
The flags parameter is the same as the like-named parameter to
bus_space_map, the same flag values should be used, and they have the
same meanings.
Handles created by bus_space_alloc() should only be freed with
bus_space_free(). Trying to use bus_space_unmap() on them causes unde-
fined behaviour. The bus_space_subregion() function can be used on han-
dles created by bus_space_alloc().
bus_space_free(space, handle, size)
The bus_space_free() function unmaps and frees a region of bus space
mapped and allocated with bus_space_alloc(). When unmapping a region,
the size specified should be the same as the size given to
bus_space_alloc() when allocating the region.
After bus_space_free() is called on a handle, that handle is no longer
valid. (If copies were made of the handle, they are no longer valid, ei-
ther.)
This function will never fail. If it would fail (e.g. because of an ar-
gument error), that indicates a software bug which should cause a panic.
In that case, bus_space_free() will never return.
READING AND WRITING SINGLE DATA ITEMS
The simplest way to access bus space is to read or write a single data
item. The bus_space_read_N() and bus_space_write_N() families of func-
tions provide the ability to read and write 1, 2, 4, and 8 byte data
items on busses which support those access sizes.
bus_space_read_1(space, handle, offset)
bus_space_read_2(space, handle, offset)
bus_space_read_4(space, handle, offset)
bus_space_read_8(space, handle, offset)
The bus_space_read_N() family of functions reads a 1, 2, 4, or 8 byte da-
ta item from the offset specified by offset into the region specified by
handle of the bus space specified by space. The location being read must
lie within the bus space region specified by handle.
For portability, the starting address of the region specified by handle
plus the offset should be a multiple of the size of data item being read.
On some systems, not obeying this requirement may cause incorrect data to
be read, on others it may cause a system crash.
Read operations done by the bus_space_read_N() functions may be executed
out of order with respect to other pending read and write operations un-
less order is enforced by use of the bus_space_barrier() function.
These functions will never fail. If they would fail (e.g. because of an
argument error), that indicates a software bug which should cause a pan-
ic. In that case, they will never return.
bus_space_write_1(space, handle, offset, value)
bus_space_write_2(space, handle, offset, value)
bus_space_write_4(space, handle, offset, value)
bus_space_write_8(space, handle, offset, value)
The bus_space_write_N() family of functions writes a 1, 2, 4, or 8 byte
data item to the offset specified by offset into the region specified by
handle of the bus space specified by space. The location being written
must lie within the bus space region specified by handle.
For portability, the starting address of the region specified by handle
plus the offset should be a multiple of the size of data item being writ-
ten. On some systems, not obeying this requirement may cause incorrect
data to be written, on others it may cause a system crash.
Write operations done by the bus_space_write_N() functions may be execut-
ed out of order with respect to other pending read and write operations
unless order is enforced by use of the bus_space_barrier() function.
These functions will never fail. If they would fail (e.g. because of an
argument error), that indicates a software bug which should cause a pan-
ic. In that case, they will never return.
BARRIERS
In order to allow high-performance buffering implementations to avoid bus
activity on every operation, read and write ordering should be specified
explicitly by drivers when necessary. The bus_space_barrier() function
provides that ability.
bus_space_barrier(space, handle, offset, datap, count)
The bus_space_barrier() function enforces ordering of bus space read and
write operations for the specified subregion (described by the offset and
length parameters) of the region named by handle in the space named by
space.
The flags argument controls what types of operations are to be ordered.
Supported flags are:
BUS_SPACE_BARRIER_READ Synchronize read operations.
BUS_SPACE_BARRIER_WRITE Synchronize write operations.
Those flags can be combined (or-ed together) to enforce ordering on both
read and write operations.
All of the specified type(s) of operation which are done to the region
before the barrier operation are guaranteed to complete before any of the
specified type(s) of operation done after the barrier.
Example: Consider a hypothetical device with two single-byte ports, one
write-only input port (at offset 0) and a read-only output port (at off-
set 1). Operation of the device is as follows: data bytes are written to
the input port, and are placed by the device on a stack, the top of which
is read by reading from the output port. The sequence to correctly write
two data bytes to the device then read those two data bytes back would
be:
/*
* t and h are the tag and handle for the mapped device's
* space.
*/
bus_space_write_1(t, h, 0, data0);
bus_space_barrier(t, h, 0, 1, BUS_SPACE_BARRIER_WRITE); /* 1 */
bus_space_write_1(t, h, 0, data1);
bus_space_barrier(t, h, 0, 2,
BUS_SPACE_BARRIER_READ|BUS_SPACE_BARRIER_WRITE); /* 2 */
ndata1 = bus_space_read_1(t, h, 1);
bus_space_barrier(t, h, 1, 1, BUS_SPACE_BARRIER_READ); /* 3 */
ndata0 = bus_space_read_1(t, h, 1);
/* data0 == ndata0, data1 == ndata1 */
The first barrier makes sure that the first write finishes before the
second write is issued, so that two writes to the input port are done in
order and are not collapsed into a single write. This ensures that the
data bytes are written to the device correctly and in order.
The second barrier makes sure that the writes to the output port finish
before any of the reads to the input port are issued, thereby making sure
that all of the writes are finished before data is read. This ensures
that the first byte read from the device really is the last one that was
written.
The third barrier makes sure that the first read finishes before the sec-
ond read is issued, ensuring that data is read correctly and in order.
The barriers in the example above are specified to cover the absolute
minimum number of bus space locations. It is correct (and often easier)
to make barrier operations cover the device's whole range of bus space,
that is, to specify an offset of zero and the size of the whole region.
REGION OPERATIONS
Some devices use buffers which are mapped as regions in bus space. Of-
ten, drivers want to copy the contents of those buffers to or from memo-
ry, e.g. into mbufs which can be passed to higher levels of the system or
from mbufs to be output to a network. In order to allow drivers to do
this as efficiently as possible, the bus_space_read_region_N() and
bus_space_write_region_N() families of functions are provided.
Drivers occasionally need to copy one region of a bus space to another,
or to set all locations in a region of bus space to contain a single val-
ue. The bus_space_copy_region_N() family of functions and the
bus_space_set_region_N() family of functions allow drivers to perform
these operations.
bus_space_read_region_1(space, handle, offset, datap, count)
bus_space_read_region_2(space, handle, offset, datap, count)
bus_space_read_region_4(space, handle, offset, datap, count)
bus_space_read_region_8(space, handle, offset, datap, count)
The bus_space_read_region_N() family of functions reads count 1, 2, 4, or
8 byte data items from bus space starting at byte offset offset in the
region specified by handle of the bus space specified by space and writes
them into the array specified by datap. Each successive data item is read
from an offset 1, 2, 4, or 8 bytes after the previous data item (depend-
ing on which function is used). All locations being read must lie within
the bus space region specified by handle.
For portability, the starting address of the region specified by handle
plus the offset should be a multiple of the size of data items being read
and the data array pointer should be properly aligned. On some systems,
not obeying these requirements may cause incorrect data to be read, on
others it may cause a system crash.
Read operations done by the bus_space_read_region_N() functions may be
executed in any order. They may also be executed out of order with re-
spect to other pending read and write operations unless order is enforced
by use of the bus_space_barrier() function. There is no way to insert
barriers between reads of individual bus space locations executed by the
bus_space_read_region_N() functions.
These functions will never fail. If they would fail (e.g. because of an
argument error), that indicates a software bug which should cause a pan-
ic. In that case, they will never return.
bus_space_write_region_1(space, handle, offset, datap, count)
bus_space_write_region_2(space, handle, offset, datap, count)
bus_space_write_region_4(space, handle, offset, datap, count)
bus_space_write_region_8(space, handle, offset, datap, count)
The bus_space_write_region_N() family of functions reads count 1, 2, 4,
or 8 byte data items from the array specified by datap and writes them to
bus space starting at byte offset offset in the region specified by
handle of the bus space specified by space. Each successive data item is
written to an offset 1, 2, 4, or 8 bytes after the previous data item
(depending on which function is used). All locations being written must
lie within the bus space region specified by handle.
For portability, the starting address of the region specified by handle
plus the offset should be a multiple of the size of data items being
written and the data array pointer should be properly aligned. On some
systems, not obeying these requirements may cause incorrect data to be
written, on others it may cause a system crash.
Write operations done by the bus_space_write_region_N() functions may be
executed in any order. They may also be executed out of order with re-
spect to other pending read and write operations unless order is enforced
by use of the bus_space_barrier() function. There is no way to insert
barriers between writes of individual bus space locations executed by the
bus_space_write_region_N() functions.
These functions will never fail. If they would fail (e.g. because of an
argument error), that indicates a software bug which should cause a pan-
ic. In that case, they will never return.
bus_space_copy_region_1(space, srchandle, srcoffset, dsthandle,
dstoffset, count)
bus_space_copy_region_2(space, srchandle, srcoffset, dsthandle,
dstoffset, count)
bus_space_copy_region_4(space, srchandle, srcoffset, dsthandle,
dstoffset, count)
bus_space_copy_region_8(space, srchandle, srcoffset, dsthandle,
dstoffset, count)
The bus_space_copy_region_N() family of functions copies count 1, 2, 4,
or 8 byte data items in bus space from the area starting at byte offset
srcoffset in the region specified by srchandle of the bus space specified
by space to the area starting at byte offset dstoffset in the region
specified by dsthandle in the same bus space. Each successive data item
read or written has an offset 1, 2, 4, or 8 bytes after the previous data
item (depending on which function is used). All locations being read and
written must lie within the bus space region specified by their respec-
tive handles.
For portability, the starting addresses of the regions specified by the
each handle plus its respective offset should be a multiple of the size
of data items being copied. On some systems, not obeying this require-
ment may cause incorrect data to be copied, on others it may cause a sys-
tem crash.
Read and write operations done by the bus_space_copy_region_N() functions
may be executed in any order. They may also be executed out of order
with respect to other pending read and write operations unless order is
enforced by use of the bus_space_barrier(function). There is no way to
insert barriers between reads or writes of individual bus space locations
executed by the bus_space_copy_region_N() functions.
Overlapping copies between different subregions of a single region of bus
space are handled correctly by the bus_space_copy_region_N() functions.
These functions will never fail. If they would fail (e.g. because of an
argument error), that indicates a software bug which should cause a pan-
ic. In that case, they will never return.
bus_space_set_region_1(space, handle, offset, value, count)
bus_space_set_region_2(space, handle, offset, value, count)
bus_space_set_region_4(space, handle, offset, value, count)
bus_space_set_region_8(space, handle, offset, value, count)
The bus_space_set_region_N() family of functions writes the given value
to count 1, 2, 4, or 8 byte data items in bus space starting at byte off-
set offset in the region specified by handle of the bus space specified
by space. Each successive data item has an offset 1, 2, 4, or 8 bytes af-
ter the previous data item (depending on which function is used). All
locations being written must lie within the bus space region specified by
handle.
For portability, the starting address of the region specified by handle
plus the offset should be a multiple of the size of data items being
written. On some systems, not obeying this requirement may cause incor-
rect data to be written, on others it may cause a system crash.
Write operations done by the bus_space_set_region_N() functions may be
executed in any order. They may also be executed out of order with re-
spect to other pending read and write operations unless order is enforced
by use of the bus_space_barrier() function. There is no way to insert
barriers between writes of individual bus space locations executed by the
bus_space_set_region_N() functions.
These functions will never fail. If they would fail (e.g. because of an
argument error), that indicates a software bug which should cause a pan-
ic. In that case, they will never return.
READING AND WRITING A SINGLE LOCATION MULTIPLE TIMES
Some devices implement single locations in bus space which are to be read
or written multiple times to communicate data, e.g. some ethernet de-
vices' packet buffer FIFOs. In order to allow drivers to manipulate
these types of devices as efficiently as possible, the
bus_space_read_multi_N() and bus_space_write_multi_N() families of func-
tions are provided.
bus_space_read_multi_1(space, handle, offset, datap, count)
bus_space_read_multi_2(space, handle, offset, datap, count)
bus_space_read_multi_4(space, handle, offset, datap, count)
bus_space_read_multi_8(space, handle, offset, datap, count)
The bus_space_read_multi_N() family of functions reads count 1, 2, 4, or
8 byte data items from bus space at byte offset offset in the region
specified by handle of the bus space specified by space and writes them
into the array specified by datap. Each successive data item is read from
the same location in bus space. The location being read must lie within
the bus space region specified by handle.
For portability, the starting address of the region specified by handle
plus the offset should be a multiple of the size of data items being read
and the data array pointer should be properly aligned. On some systems,
not obeying these requirements may cause incorrect data to be read, on
others it may cause a system crash.
Read operations done by the bus_space_read_multi_N() functions may be ex-
ecuted out of order with respect to other pending read and write opera-
tions unless order is enforced by use of the bus_space_barrier() func-
tion. Because the bus_space_read_multi_N() functions read the same bus
space location multiple times, they place an implicit read barrier be-
tween each successive read of that bus space location.
These functions will never fail. If they would fail (e.g. because of an
argument error), that indicates a software bug which should cause a pan-
ic. In that case, they will never return.
bus_space_write_multi_1(space, handle, offset, datap, count)
bus_space_write_multi_2(space, handle, offset, datap, count)
bus_space_write_multi_4(space, handle, offset, datap, count)
bus_space_write_multi_8(space, handle, offset, datap, count)
The bus_space_write_multi_N() family of functions reads count 1, 2, 4, or
8 byte data items from the array specified by datap and writes them into
bus space at byte offset offset in the region specified by handle of the
bus space specified by space. Each successive data item is written to the
same location in bus space. The location being written must lie within
the bus space region specified by handle.
For portability, the starting address of the region specified by handle
plus the offset should be a multiple of the size of data items being
written and the data array pointer should be properly aligned. On some
systems, not obeying these requirements may cause incorrect data to be
written, on others it may cause a system crash.
Write operations done by the bus_space_write_multi_N() functions may be
executed out of order with respect to other pending read and write opera-
tions unless order is enforced by use of the bus_space_barrier() func-
tion. Because the bus_space_write_multi_N() functions write the same bus
space location multiple times, they place an implicit write barrier be-
tween each successive write of that bus space location.
These functions will never fail. If they would fail (e.g. because of an
argument error), that indicates a software bug which should cause a pan-
ic. In that case, they will never return.
EXPECTED CHANGES TO THE BUS_SPACE FUNCTIONS
The definition of the bus_space functions should not yet be considered
finalized. There are several changes and improvements which should be
explored, including:
o Providing a mechanism by which incorrectly-written drivers will be
automatically given barriers and properly-written drivers won't be
forced to use more barriers than they need. This should probably be
done via a #define in the incorrectly-written drivers. Unfortunate-
ly, at this time, few drivers actually use barriers correctly (or at
all). Because of that, bus_space implementations on architectures
which do buffering must always do the barriers inside the bus_space
calls, to be safe. That has a potentially significant performance
impact.
o Exporting the bus_space functions to user-land so that applications
(such as X servers) have easier, more portable access to device
space.
o Redefining bus space tags and handles so that machine-independent bus
interface drivers (for example PCI to VME bridges) could define and
implement bus spaces without requiring machine-dependent code. If
this is done, it should be done in such a way that machine-dependent
optimizations should remain possible.
o Converting bus spaces (such as PCI configuration space) which cur-
rently use space-specific access methods to use the bus_space func-
tions where that is appropriate.
o Redefining the way bus space is mapped and allocated, so that mapping
and allocation are done with bus specific functions which return bus
space tags. This would allow further optimization than is currently
possible, and would also ease translation of the bus_space functions
into user space (since mapping in user space would look like it just
used a different bus-specific mapping function).
COMPATIBILITY
The current version of the bus_space interface specification differs
slightly from the original specification that came into wide use. A few
of the function names and arguments have changed for consistency and in-
creased functionality. Drivers that were written to the old, deprecated
specification can be compiled by defining the __BUS_SPACE_COMPAT_OLDDEFS
preprocessor symbol before including <machine/bus.h>.
HISTORY
The bus_space functions were introduced in a different form (memory and
I/O spaces were accessed via different sets of functions) in NetBSD 1.2.
The functions were merged to work on generic ``spaces'' early in the
NetBSD 1.3 development cycle, and many drivers were converted to use
them. This document was written later during the NetBSD 1.3 development
cycle and the specification was updated to fix some consistency problems
and to add some missing functionality.
AUTHORS
The bus_space interfaces were designed and implemented by the NetBSD de-
veloper community. Primary contributors and implementors were Chris
Demetriou, Jason Thorpe, and Charles Hannum, but the rest of the NetBSD
developers and the user community played a significant role in develop-
ment.
Chris Demetriou wrote this manual page.
SEE ALSO
bus_dma(9)
NetBSD August 13, 1997 14