intr(D2)intr(D2)NAMEintr - process a device interrupt
SYNOPSIS
void prefixintr(int ivec);
Arguments
ivec Number used by the operating system to associate a driver's
interrupt handler with an interrupting device. For a VME
device, this number can be the logical device number, the
interrupt vector number, or the address which is set by
vme_ivec_set(). For a SCSI device, this number is a pointer to
a scsi_request_t type structure.
DESCRIPTION
The intr routine is the interrupt handler for both block and character
hardware drivers, as well as for non-driver hardware modules.
Return Values
None
USAGE
This entry point is only required for those modules that interface to
hardware that interrupts the host computer. It is not used with software
drivers.
The interrupt handler is responsible for determining the reason for an
interrupt, servicing the interrupt, and waking up any base-level driver
processes sleeping on any events associated with the interrupt.
For example, when a disk drive has transferred information to the host to
satisfy a read request, the disk drive's controller generates an
interrupt. The CPU acknowledges the interrupt and calls the interrupt
handler associated with that controller and disk drive. The interrupt
routine services the interrupt and then wakes up the driver base-level
process waiting for data. The base-level portion of the driver then
conveys the data to the user.
In general, most interrupt routines do the following tasks:
keep a record of interrupt occurrences
return immediately if no devices controlled by a driver caused the
interrupt (only for systems supporting shared interrupts)
interpret the interrupt routine argument ivec
reject requests for devices that are not served by the device's
controller
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process interrupts that happen without cause (called spurious
interrupts)
handle all possible device errors
wake processes that are sleeping on any events associated with the
interrupt
There are also many tasks the intr routine must perform that are driver-
type and device specific. For example, the following types of drivers
require different functions from their intr routines:
A block driver dequeues requests and wakes up processes sleeping on
an I/O request.
A terminal driver receives and sends characters.
A printer driver ensures that characters are sent.
In addition, the functions of an intr routine are device dependent. You
should know the exact chip set that produces the interrupt for your
device. You need to know the exact bit patterns of the device's control
and status register and how data is transmitted into and out of your
computer. These specifics differ for every device you access.
The intr routine for an intelligent controller that does not use
individual interrupt vectors for each subdevice must access the
completion queue to determine which subdevice generated the interrupt.
It must also update the status information, set/clear flags, set/clear
error indicators, and so forth to complete the handling of a job. The
code should also be able to handle a spurious completion interrupt
identified by an empty completion queue. When the routine finishes, it
should advance the unload pointer to the next entry in the completion
queue.
If the driver called biowait(D3) or sleep(D3) to await the completion of
an operation, the intr routine must call biodone(D3) or wakeup(D3) to
signal the process to resume.
The interrupt routine runs at the processor level associated with the
interrupt level for the given device. Lower priority interrupts are
deferred while the interrupt routine is active. Certain processor levels
can block different interrupts. See spl(D3) for more information.
uiomove(D3), ureadc(D3), and uwritec(D3) cannot be used in an interrupt
routine when the uio_segflg member of the uio(D4) structure is set to
UIO_USERSPACE (indicating a transfer between user and kernel space).
Synchronization Constraints
The intr routine must never:
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use functions that sleep
drop the interrupt priority level below the level at which the
interrupt routine was entered
call any function or routine that requires user context (that is, if
it accesses or alters information associated with the running
process)
REFERENCESbiodone(D3), biowait(D3), spl(D3), wakeup(D3), vme_ivec_set(D3X)
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