OpenBus System - Configuring Clock, Reset and Interrupt Lines

Management of the clock, reset and interrupt lines for the system are handled in the OpenBus Signal Manager dialog – accessed by clicking on the button on the OpenBus toolbar (or using the Tools » OpenBus Signal Manager command). These signals are handled separately from the bus interface, leaving the interface to be just the base set of standard bus signals.

Clock and reset signals across all components in the system are listed over the Clocks and Resets tabs of the dialog, respectively (Figure 1).

Figure 1. Defining clock and reset lines for the OpenBus System.

You can have all clock/reset lines connected to a single, default clock/reset net, such as CLK_I/RST_I. Alternatively, you can specify a particular net to which to connect to, on an individual component basis.

Use of processor interrupt pins by slave peripheral devices is determined on the Interrupts tab of the dialog (Figure 2).

Figure 2. Defining interrupt lines for the OpenBus system.

All interrupt-generating slave peripheral devices defined in the OpenBus System are listed, further broken down into the individual interrupt lines they can provide. Each processor used in the system will have a dedicated column. Use this column to specify which of the processor's interrupt pins, if any, are to be used by the interrupt lines of each slave device.

Figure 3. Assigning a
processor interrupt line to a
slave peripheral device.

Each interrupt line has an accompanying (and uneditable) graphical depiction of its Kind – whether it is level-sensitive or edge-triggered – as well as its polarity.

Beneath the specific list of defined OpenBus peripherals and their interrupts, there is a complete listing of all interrupt pins for the processor, allowing the ability to export interrupt lines.

If an interrupt line is not currently assigned to an OpenBus peripheral, it can be made available as an input pin on the top-level design schematic. This enables you to import an interrupt from a peripheral device external to the OpenBus System document. Simply use the associated drop-down field and set the entry to Exported (as input pin).

Figure 4. Exporting a processor interrupt line for use as input by an external peripheral device.

The Kind and Polarity field will become editable, from where you can specify the type of interrupt being imported on this line (Figure 5).

Figure 5. Setting interrupt kind for the external interrupt.

If an interrupt line is currently assigned to an OpenBus peripheral, it can be made available as an output pin on the top-level design schematic. This enables you, for example, to export an interrupt for debugging purposes, or for connection to a processor that resides on the schematic sheet. Simply set the entry in the associated field for the interrupt to Exported (as output pin). Figure 6 illustrates this for a series of processor interrupt pins assigned for use by internal OpenBus peripheral devices.

Figure 6. Exporting processor interrupt lines for use outside of the OpenBus System.

Note: An exported interrupt will change from being an input pin to an output pin, if that interrupt becomes assigned to an OpenBus peripheral component. If the interrupt is no longer connected to the OpenBus peripheral, the exported interrupt will change from output pin to input pin. In all cases, resynchronization between the sheet entries on the top sheet and the ports of the OpenBus System document must be performed.

For interrupt pin INT_I0, there is an additional entry that can be chosen – Internal. This allows for the situation where the INT_I0 line of the processor is actually the logical OR of the interrupt generated by a Programmable Interval Timer, internal to the processor, and the interrupt line zero. Provided the interrupt is not assigned to an OpenBus peripheral, the Internal entry will be available. When this option is used, the interrupt pin will not be exported for use outside the OpenBus System. Note however, that precedence is given to use of the interrupt line by an OpenBus peripheral. If you have set the Internal option for the pin, then subsequently assign INT_I0 for a peripheral's interrupt line, the setting will automatically be changed to Exported (as output pin).

For an example of exporting interrupt lines, see Handling External Interrupts in an OpenBus System.