Bailey O.H.Embedded systems.Desktop integration.2005

Development Strategy

Unlike the BASIC Stamp, we will be using several languages and components to demonstrate the PIC implementation. We will develop two solutions using PIC processors; here’s why: The PIC processor line has an older part that supports low-speed USB. This part comes in a 28and 40-pin version (16C747/16C765). These parts are “one-time” programmable, which means they can’t be reprogrammed. These chips are used in two different demo kits: the PICKit 1 and the PICDEM USB. The PICKit 1 is a very inexpensive (under $40) tool that uses the 16C745 part as a USB programmer for other Microchip parts. The board has a flash-based 12F675 part that can be programmed via the USB port on a Windows PC. There are LEDs for simulating output on the target part, a push button switch, and pot for input. There is also another program that expands the variety of parts that the board can program. All of the source code to the USB part, the Windows portion, and sample target programs are included along with data books in PDF format. The board has a “break-away” prototype board that can be used to interface the sample 12F675 to the world.

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What Is HIDmaker?

HIDmaker is a unique product that assists embedded developers who use the 16C745 chips to develop their data flow and Windows HID interface. To understand the usefulness of this product you need to first understand what HID is. In the Windows operating system Microsoft implemented a tiered device driver scheme so developers of human interface devices (HID) like trackballs, mice, and keyboards could quickly bring their products to market. If this sounds unique to Microsoft, it isn’t. The USB specification includes the HID driver interface. The idea is that all human interface devices share some common properties, so the USB implementer forum decided to include a higher level interface just for such devices. The device type determines how the low-level driver that is part of the operating system will handle data to and from these devices and use one of the built-in handlers or a vendor-installed handler.

HIDmaker wraps code around the PIC USB firmware to bring the embedded systems into the HID data handling specification. So code is generated for the embedded processor, and a Windows HID driver interface with the data handling layout and scheme are also generated. When completed, the wrapper code for the PIC is embedded into the chip along with the USB firmware and a listing in the language of your choice is created for the Windows driver. So what about Linux and UNIX? This is a book about cross-platform development. The truth is that Linux allows the developer to handle this without a tiered driver interface. We will cover this topic in Chapter 11.

Chapter 9

Embedded

Compile / Test

Compile for 16C745 / 16C765

method we used in Chapter 7 to build an interchangeable RS-232/USB/Ethernet interface. The difference here (aside from using different components) is that we are building both the USB interface and embedded controller. Once we have completed the dsPIC thermostat interface, the only remaining task is to be certain we can use either the low-speed 16C745 or full-speed 18F2455 devices. So let’s begin by writing the necessary software to interface our dsPIC to the thermostat boards.

For this example will use the Microchip C30 compiler and ICD 2. These combined with MPLAB will afford us the ability to not only develop but also debug our code at the source level as well. To develop our prototype we will use a modified version of the dsPICDEM 28 board, which provides us with a dsPIC 2010 28-pin part, reset switch, power LED, program-accessible LED, power interface, RS-232 interface, and a prototype area.

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Figure 9-7

There are two ways to debug embedded systems using the PIC processor line. The first tool is the ICD that we’ve been discussing. The ICD is very versatile in that it also allows you to reprogram the chip in circuit on the finished board in the field. For debugging purposes it is an excellent tool; however, it does use the target processor pins so if you are are debugging, the I/O pins used for the debugger are unavailable for I/O. Second, your target board has to be working and powered. The alternative to the ICD is the in-circuit emulator, or ICE as it’s commonly called. The ICE is a small device that looks like a black box with a ribbon cable coming out of it. The ICE unit actually emulates the processor so you can download and run code without using any processor pins at all. The ICE also has its own power supply so it doesn’t need to be connected to anything other than the development system to work. The difference in price is considerable as the ICD is around $150 and the ICE is around $4,000. If you’re doing time-sensitive or real-time development, the ICE is the way to go. For our purposes, the ICD will work fine so we will develop using it.

Chapter 9

The dsPIC Code Development

Environments

Before we continue let’s get familiar with the dsPIC and the PIC development IDE MPLAB. MPLAB is a free IDE provided by Microchip, the same people who make the PIC and dsPIC products. MPLAB contains support for a simulator, debugger, programmer, and third-party tools. All of the code we develop will be written in C. The first compiler we will use is the C30 product from Microchip. This compiler is an enhanced GNU compiler that provides support for the dsPIC family of processors. We will also be using the language tools library that is included with the C30 product but can also be freely downloaded. This library provides C language wrappers around the silicon impementation of the communications and I/O functions we will need for this prototype. We will also use the HI-TECH dsPICC compiler, which is ANSI compliant, for one of our sample programs. HI-TECH also provides C compilers for all of the PIC products. We will also use the C18 and PIC18 products for developing software for the 18F4550 USB chip and PicBasic Pro for developing and testing code for the older 16C745 low-speed USB chip.

The MPLAB IDE

To provide a consistent development interface, we will use MPLAB 7 from Microchip. MPLAB is free and available for download from www.microchip.com; look for it under development tools. MPLAB includes a built-in simulator, programmer support, debugger support, and support for most third-party tools. We will be using C30 and C18 from Microchip, PICC Enterprise from HI-TECH software, and PicBasic Pro from microEngineering Labs. This combination of tools will give us varied experience along with the quickest path to completion. Once you’ve installed MPLAB an icon on your desktop is used to

Chapter 9