Published online by Cambridge University Press: 26 February 2010
This chapter focuses on synthesis-based asynchronous controller design. Such designs use a bounded delay model, similarly to synchronous circuits. In this particular design methodology the datapath is decoupled from the control logic. Often the very same synchronous datapath can be used directly, with minor modifications.
Figure 8.1 below illustrates a synthesis-based controller in a synchronous pipeline, providing the clock (Clk) to the flip-flops. A separate synthesis-based controller can be designed uniquely for each stage of the pipeline, or a more general circuit can be specified and synthesized to fit all pipeline stages. Figure 8.1(a) illustrates a standard synchronous pipeline. In Figure 8.1(b) the Clk signal has been stripped out of the pipeline, and the controllers are placed so as to provide the latching signal for the flip-flops.
In this chapter we will first present some background on burst-mode circuits and on ways to build these controllers. We will then review approaches for building input–output circuits from signal transition graph specifications.
Fundamental-mode Huffman circuits
In the fundamental-mode style, circuits consist of a network of combinational gates that take inputs, move the circuit from one state to another, generate outputs, and also generate the next-state logic, similarly to the way in which standard synchronous circuits operate. The next-state outputs feed back through the delay elements and arrive at the inputs of the controller as the current state. Sometimes delays on feedback paths are necessary, however, they are not shown explicitly in Figure 8.2.
To save this book to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.