Paper presented at EuroPLoP 2006 Meeting real-time constraints using “Sandwich Delays” Michael J. Pont, Susan Kurian and Ricardo Bautista Embedded Systems Laboratory, University of Leicester, University Road, LEICESTER LE1 7RH, UK. M.Pont@le.ac.uk ; sk183@le.ac.uk ; rb169@le.ac.uk http://www.le.ac.uk/eg/embedded/ Abstract This short paper is concerned with the use of patterns to support the development of software for reliable, resource-constrained, embedded systems. The paper introduces one new pattern (SANDWICH DELAY) and describes one possible implementation of this pattern for use with a popular family of ARM-based microcontrollers. Introduction In this paper, we are concerned with the development of software for a class of embedded systems in which there are two (sometimes conflicting) constraints. First, we wish to implement the design on a microcontroller with a cost of around $1.00 (US). This type of platform might include an 8-bit or 16/32-bit microcontroller with very limited memory and CPU performance. Second, we wish to produce a system with extremely predictable behaviour. These behavioural constraints are of a hard real-time nature: for example, we typically require that the interval between the start times of periodic tasks does not vary by more than 1 µs (preferably less). To support the development of this type of software, we have previously described a “language” consisting of more than seventy patterns (e.g. see Pont, 2001). Work began on these patterns in 1996, and they have since been used it in a range of industrial systems, numerous university research projects, as well as in undergraduate and postgraduate teaching on many university courses (e.g. see Pont, 2003; Pont and Banner, 2004). This brief paper describes one new pattern (SANDWICH DELAY) and illustrates – using what we call a “pattern implementation example” (e.g. see Kurian and Pont, 2005) one possible implementation of this pattern for use with a popular family of ARM-based microcontrollers. Acknowledgements Many thanks to Bob Hanmer, who provided numerous useful suggestions during the shepherding process. Copyright Copyright © 2006 by Michael J. Pont, Susan Kurian and Ricardo Bautista. Permission is granted to copy this paper for use in association with the EuroPLoP 2006 conference. MT3-1