2.1. About the functions

Figure 2.1 shows the CoreLink QoS-301 Network Interconnect Advanced Quality of Service in position in the CoreLink NIC-301 Network Interconnect.

Figure 2.1. CoreLink NIC-301 Network Interconnect with CoreLink QoS-301 Advanced Quality of Service top-level diagram

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Example 2.1 contains an animation that shows the following masters, on the left-hand side of a NIC-301 interconnect:

These masters send random requests to the DMC slave on the right-hand side of the interconnect through the switches inside the interconnect. The DMC must process the requests and send responses back to the masters to service them. When a master sends a request, the number of outstanding transactions in the counter on the right-hand side of the animation increases by one. When the DMC slave services one of these transactions by sending a response, the number of outstanding transactions on the DMC decreases by one. In a system that does not use QoS-301, the number of outstanding transactions can increase up to the limit of the memory controller, at which point, the last master to send a request is not serviced. In Example 2.1, the memory controller can handle a maximum of 12 transactions.

The animation in Example 2.1 shows a situation in which the DMC slave cannot process the requests quickly enough, and the number of outstanding transactions reaches the critical limit of the maximum number of outstanding transactions.

Example 2.1. Animation showing transactions and responses in a NIC-301 interconnect that does not use QoS-301

To play the movie for the first time after opening the PDF file, left-click on the diagram. Acrobat Gives you the following choices for how to play the movie:

Play the multimedia content this one time

If you select this option, Acrobat plays the animation once, but the next time you open the PDF file, Acrobat prompts you with the same question and does not consider the document to be trusted. Acrobat prompts you with the same question each time you open the PDF file from new.

Play the multimedia content and add this document to my list of trusted documents

If you select this option, Acrobat plays the animation once, and the next time you open the PDF file, it remembers that this is a trusted document, and does not prompt you with the same question again.

To play the movie again after the first time, right-click on the animation below and select Play. If you right-click and select Loop, the next time you play the movie, Acrobat repeats the movie continuously from start to end.

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Example 2.2. Animation showing transactions and responses in a NIC-301 interconnect that uses QoS-301

The masters send random requests to the DMC slave on the right-hand side of the interconnect through the QoS-301 regulators and switches. The QoS-301 regulators for the DMA controller and graphics processor each have a maximum number of outstanding transactions that you specify, in this example, four and five respectively. In the same way as in Example 2.1, the DMC must service the requests by sending responses back to the masters. With QoS-301 implemented, the DMC services the requests it receives for each master, until the Qos regulator for that master reaches its limit, the maximum number of outstanding transactions. This means that real-time-critical masters such as the LCD controller never fail to have their requests serviced, and no visible disruption occurs because by not adding a QoS-301 regulator for the LCD controller, as is the case in Example 2.2, whenever the LCD controller issues a request, the DMC services it immediately. The ARM processor also has no regulator, so its requests gain priority over the DMA controller and the graphics processor.

The animation in Example 2.2 shows the situation where the DMC responds to requests for the LCD controller and ARM processor when the other channels, for the DMA controller and graphics processor, are blocked because they have reached their individual limits for the maximum number of outstanding transactions.

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QoS configuration options are available on:

Note

You program the QoS-301 blocks from the NIC-301 global programmers view.

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