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from an engineer Understanding the VXI/VME Interrupt and Signal Acknowledge Cycle
The VME bus specification defines the Priority Interrupt Bus in order that a VME gadget can
asynchronously request support from a controller. This offers a VME/VXI device a way of finding
the controller’s attention at any time.
A VXI/VME bus method has seven interrupt lines bodily related to all slots in the chassis.
This document addresses interrupts on each VME and VXI systems.
Interrupt line seven has the highest priority, and interrupt line one has the lowest priority.
Additionally to your real interrupt lines, the Priority Interrupt Bus also consists of a
daisy-chained interrupt acknowledge signal and aspects of the Data Transfer Bus
(the info lines, the data acknowledge line, as well as the reduce three handle lines).
The table beneath summarizes every signal used in the Priority Interrupt Bus and
summarizes the perform of every signal. A system that requests service by asserting
one particular from the interrupt lines is called an interrupter. A useful device known as
an interrupt handler companies the interrupt. There might be more than one
interrupt handler in a VXI/VMEbus program. Countrywide Instruments embedded controllers
and exterior MXI bus controllers enable you to configure multiple interrupt handlers
(from 1 to 7).
Table I. Priority Interrupt Bus Signals
Signal
Function
IRQ1*-IRQ7*
An interrupter uses this signal to indicate that it is requesting services.
IACK*
An interrupt handler uses this signal to indicate that it has received an interrupt and is ready to receive a status/ID that will tell the handler how to proceed with servicing the interrupt.
IACKIN*/
IACKOUT*
A module receives the IACK* on IACKIN*. It places a status/ID on the bus if the interrupt level being serviced matches the module’s interrupt level and if the device is interrupting. Otherwise, the module passes the signal on using IACKOUT*.
A01-A03
The interrupt handler asserts these lines with the value corresponding to
the interrupt level being serviced.
D00-D31
The interrupter being serviced places the status/ID on these lines once IACK* has been received.
DTACK*
The interrupter uses this signal to indicate that its status/ID is asserted on the knowledge lines.
A much more detailed explanation of what happens inside the interrupt cycle is outlined below.
A gadget that requests support by asserting 1 of your interrupt lines is known as an interrupter. A useful gadget known as an interrupt handler services the interrupt. There might be over 1 interrupt handler within a VXI/VME bus program. However, there can only be a single interrupt handler per interrupt level inside the program. Countrywide Instruments embedded controllers and external MXI bus controllers let you configure multiple interrupt handlers (from one to seven).
Therefore,
Office Professional Product Key, two types of interrupt handler methods are possible:
A single handler system A distributed system
Within a single handler program, one particular interrupt handler gadget services all interrupt lines. In a distributed system, there are two or far more handlers, every single servicing an exclusive subset of your 7 interrupt lines. Most systems are single handler methods, where the program controller handles all interrupt lines in the chassis. It is possible for VXI devices to act as programmable interrupt handlers, but this is not very common. The Useful resource manager detects programmable VXI interrupt handlers and uses information stored in the device’s configuration registers to assign the interrupt levels that will be handled by the VXI device. Note that VME devices do not define a standard set of configuration registers - you must use Test and Measurement Explorer or VXI Edit/vxitedit to enter any configuration information associated with the VME system.
There are two types of interrupters:
Release On ACKnowledge (ROAK) Release On Register Access (RORA)
Most VXI and VME instruments fall under the ROAK category and also the sequence of events described under is only applicable to ROAK devices.
The Sequence of Events During an Interrupt (IACK*) Cycle
After a gadget asserts an interrupt, it waits for a response from the interrupt handler. When the interrupt handler detects that an interrupt line has been asserted,
Office 2007 Professional Plus Product Key, the interrupt handler asserts the IACK* (interrupt acknowledge) signal. It also sets the reduced 3 tackle lines A01 – A03 to indicate which interrupt line it is trying to acknowledge with the IACK* signal. The IACK* line that the handler drives is related to your IACKIN* pin of slot 0 from the chassis (Slot one in VME bus techniques). If the module in the first slot is not asserting the interrupt line being acknowledged,
Microsoft Office Standard, the module must propagate the IACK* signal to its IACKOUT* pin, which is related for the next slot’s IACKIN* pin. The propagation with the IACK* signal from slot to slot continues until the IACK* signal reaches the first module that is interrupting on the line being acknowledged. When the interrupter sees IACK*, it places its status/ID on the data/bus.
The interrupt handler reads the status/ID. Because the interrupt lines are open collector lines, more than one particular gadget can assert the same interrupt line at the same time. Therefore, the module asserting the interrupt does not propagate the IACK* signal. This action prevents other devices that are interrupting on the same line from finding the IACK* signal and attempting to respond at the same time. After the interrupt handler companies the interrupter, the interrupter releases the line. If other devices are interrupting on the same line, the handler then begins another interrupt acknowledge cycle to services the next interrupter on that line. The following figure illustrates the interrupt acknowledge daisy-chain.
Figure 1. Interrupt Acknowledge Daisy-Chain
Note: RORA devices require you to read/write a device certain register in order to complete the interrupt acknowledge cycle.
In this figure, the device in slot 4 has asserted an interrupt. The figure shows that if a lot more than one particular gadget asserts the same interrupt line, the system closest to slot 0 (slot 1 in VME) has the highest priority for interrupt services because it receives the IACK* signal first. The next closest device has the next highest priority, and so on. It is important to remember that the IACK daisy chain must be connected across unoccupied backplane slots, or else interrupts coming from devices to your right with the empty slot will not be acknowledged. Most chassis have jumperless backplanes where this daisy-chain connection happens automatically. However, on older backplanes that are jumpered, jumpers must be employed to connect the IACK daisy chain across unoccupied slots. On jumpered backplanes, you should also pull the jumpers from the occupied slots to ensure that the IACK daisy-chain is not mistakenly related through the slot containing the interrupter.
Status/ID Value
The status/ID in most VME techniques is an 8-bit value. In VXI techniques, the status/ID is either a 16-bit or 32-bit status/ID value. Message-Based devices that have interrupter capability must return at least a 16-bit status/ID with an optional 32-bit value. Currently, 32-bit status/IDs are uncommon. In VME systems, the status/ID is usually a vector. The processor uses this vector to calculate an address to a position in an interrupt jump table. The entry in that table is the tackle of your start of the interrupt support routine.
Therefore, when the processor handles the interrupt and receives the status/ID,
Office Home And Student 2010 Key, it jumps directly to the beginning from the interrupt services routine and executes the interrupt support routine code. The technique integrator installs the interrupt service routine at the memory location that the jump table specifies.
In VXI methods (and all Countrywide Instruments VXI/VME Controllers), the status/ID is no longer a
vector. It is de-coupled from the processor operation. After the interrupt handler receives the
status/ID, controller software invokes the appropriate support subroutine and passes the
status/ID value towards the subroutine.
The general format of the status/ID for a Register-Based VXI gadget is shown
inside the following table.
Table II. General Status/ID Format for VXI Bus Devices
Bits
31-16
15-8
7-0
Contents
Device-Dependent
Cause/Status
(Device-Dependent)
Logical Address
of Interrupter
For Message-Based VXI devices, there is a further definition of your status/ID format. The status/ID can take on either a Response format or an Event format. Under the Event Format, bit 15 with the status/ID must be set. The values of status/ID bits 8 through 14 define the Event condition. The VXI bus specification currently defines these bits for three specific events. It also defines a syntax for defining your own events. The events defined from the VXI bus specification and their corresponding values for status/ID bits 8 through 15 are listed below.
No Cause Given (0xFF) - This event is sent by a Register-Based gadget that has only one reason to signal its Commander. Usually, this event is issued when an operation completes.
Request True (0xFD) — This event is sent by a device when the device requires service.
Request False (0xFC) — This event is sent by the device when the system no longer requires support. The VXI bus specification also defines a syntax for sending user-defined
events. This format specifies that bit 15 must be 1 and bit 14 must be 0. Bits 8 – 13 can then be used to specify a user-defined event, as shown in the following table.
Table III. Message-Based System Status/ID—User-Defined Event Format
Bits
31-16
15
14
13-8
7-0
Contents
Device-Dependent
1
0
User-Defined Event
Logical Address
of Interrupter
Except for defining the decrease 8 bits of your status/ID value to be the logical handle of the interrupter,
Windows 7 Professional, the VXI bus specification defines only a few specific values of the status/ID. Usually, when you are working with a device capable of producing interrupts, you need to refer to your documentation accompanying the gadget to see what meaning, if any, the other bits of your status/ID have. Often, you control the conditions under which the interrupt is generated, along with the true status/ID is not important because you will know in advance why the device is sending interrupts.
Signals
Instead of asserting an interrupt line, some devices can request service by producing a signal. "Signal" in this context is not an electrical signal (such as the backplane signals discussed earlier inside the course), but rather a write of the 16-bit value for the signal register of another device. The signal register is simply a VXI configuration register that has a value written to it by another system capable of taking control of your bus. Not all devices implement a signal register. The term signal originates from its use in UNIX, where a signal is a means of inter-process communication. To use signals, the following two conditions must apply:
The signaling gadget must be able to take control with the VXI bus The gadget to which the signal is being sent must implement a signal register.
The signaling gadget uses the Info Transfer Bus to write a 16-bit value towards the signal register, which is located at offset 8 from the configuration registers for the system being signaled. The 16-bit value has exactly the same format as the 16-bit status/ID.
The procedure for handling a signal through software is the same as for an interrupt. The processes discussed above for signals and the interrupt cycle happen completely on the hardware level. These processes are transparent to a user’s application. When a controller senses an interrupt or sees that its signal register has been written to, the controller generates a local processor interrupt that lets the software driver know the event has occurred.
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