Configuring the Arbiter Component

Configuration of an Arbiter component is performed using the Configure OpenBus Arbiter dialog (Figure 1). Access this dialog by right-clicking over the component and choosing the Configure command from the menu that appears. Alternatively, double-click on the component to access the dialog directly.

Figure 1. Configuration dialog for the Arbiter component.

If you are familiar with configuration of the WB_MULTIMASTER component in the schematic world, you will appreciate the reduced level of information required to configure the Arbiter component. The OpenBus System handles much of the configuration for you, so information such as data and address bus widths are no longer defined manually.

Only two pieces of information are required through the dialog to configure the Arbiter – the mode in which the masters access the shared slave(s), and which master will be granted immediate access to the slave(s) when the Arbiter is in an "Idle" state. These are the access Type and the Master With No Delay properties, respectively.

Type

Use this area of the dialog to specify the way in which the bus masters contest for the slave device. Although the modes of access are the same as those for the WB_MULTIMASTER, the workings of each mode are different:

• Round Robin – masters access the slave in sequence, starting with the master that has been set to have no delay. For example, if you have four masters linked to the Arbiter component via slave ports s0..s4, and the master with no delay is set to be s3, then the order of access will be s3, s4, s0, s1, s2, s3, and so on.

• Priority – masters access the slave in strict sequence, starting with the slave connected to port s0 (highest priority). For example, if you have four masters linked to the Arbiter component via slave ports s0..s4, then the order of access will be s0, s1, s2, s3, s4.

Visible port numbers allow you to quickly identify each slave port of an Arbiter component and therefore simplifies wiring up the master devices in the required order.

Master With No Delay

Use this option to specify one master to be granted instant access to the bus when the Arbiter component is 'idle'. This reduces latency as the nominated master experiences no delay in acquiring access. Typically, when operating in Priority mode, the master specified here will be the one assigned highest priority, and so would be connected to port s0 of the Arbiter.

The master with no delay is distinguished graphically on the Arbiter component by use of red text for its port number (Figure 2).

Figure 2. Graphically depicting the master with no delay.