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Opportunities stack up

Bluetooth has great potential for in car communications. By Peter Lieberwirth.

Bluetooth wireless technology is set to take off next year and we are likely to see a massive increase in the number and type of Bluetooth applications from oems in many different industries.

The automotive industry is no exception: many manufacturers and suppliers are already looking at ways that Bluetooth can be used to reduce internal cabling requirements, simplify short range connectivity and reduce the cost of such vehicle such as mobile 'phones and in car entertainment.

To address these requirements, Toshiba is working closely with a number of partners to provide the hardware, software and development tools to simplify the design and implementation of Bluetooth automotive applications.
Any product that uses Bluetooth technology must, of course, adhere to the detailed guidelines documented in the lengthy and highly technical Bluetooth specification. Using the 'layer' concept (see Figure 1), this specification defines what elements or 'layers' are needed to implement Bluetooth. As the diagram shows, the layers define the various levels and protocols required in both the Bluetooth host and the module. For automotive designers, it is the implementation of the host element that will be of the most importance.

To minimise component count and simplify design, most automotive engineers tasked with implementing Bluetooth will be looking to base their designs around a single microprocessor solution. It is probable that this microprocessor will be expected to use OSEK – the real time operating system (rtos) developed specifically for the automotive industry – and to incorporate the embedded Bluetooth stack.

The Bluetooth stack is a software library that implements all of the communications protocols defined in the Bluetooth specification. Typically, the stack will provide an application programming interface (api) that ensures the developer needs only to understand how the api – rather than the whole Bluetooth stack – operates in order to produce a working Bluetooth design.

The key elements of the Bluetooth stack are: the host controller interface (hci) layer, for communications between the stack and the Bluetooth module; the logical link control and adaptation protocol (L2CAP) layer, which allows multiple channels to share the same Bluetooth link; the RFCOMM layer, which implements a virtual RS232 channel; and the Service Discovery Protocol (SDP) layer, for querying Bluetooth devices for supported functionality. In addition, there is the api itself and a transport layer that provides the relevant communication with the uart or usb drivers that manage communication with the Bluetooth module.

As might be expected, the time and resources required to develop and verify a Bluetooth stack prevent most companies from choosing to do this in house. Instead, they prefer to look to third party developers who can provide 'off the shelf' stacks for their Bluetooth applications. One of the problems to date, however, is that many third party stacks have been developed specifically for use in large host systems that have access to significant levels of resources. As a result, these stacks are often too 'resource hungry' for embedded designs that, by their very nature, demand much leaner and more efficient implementations.

Fortunately, a growing number of commercially available Bluetooth stacks have been developed from the 'ground up' for use in embedded designs. A good example comes from Swedish company IAR Systems, which specialises in the development of software for microprocessors and embedded designs.

The IAR stack has been developed using compact and efficient coding to ensure a very small memory footprint. It can also be optimised to provide only the elements of the stack needed in a given application.
Using the IAR MakeApp development tool, for instance, generated stacks can be occupy less than 30kbyte of rom. The latest version of IAR's Bluetooth stack provides all the support needed for hci, L2CAP, RFCOMM, SDP, GAP (the generic access profile that manages connections between Bluetooth devices) and the uart and USB transport link layers, as well as a serial port profile.

In addition, IAR has recently announced support for the Bluetooth Headset profile. This part of the Bluetooth specification handles voice transmission between headsets and audio gateways such as mobile telephones. Finally, the stack has been ported and tested on an OSEK implementation from Vektor Informatik to provide a ready made Bluetooth protocol stack solution for automotive applications.

To further simplify the design and implementation of Bluetooth automotive applications, IAR and Toshiba recently announced a partnership in which IAR's Bluetooth protocol stack has been adapted and optimised for use with Toshiba's TLCS-900-H2 series of microcontrollers. These 32bit cisc devices, developed to ensure optimum efficiency, will in many cases, meet the needs of automotive designers who require high performance but who do not want to move to a risc based architecture.

The TMP94FD53, one of the latest devices in the TLCS-900-H2 series, has been designed to deliver performance and power consumption levels comparable to that of risc devices. At the heart of the device is Toshiba's TLCS900/H2 processor core. This core features an internal 32bit structure and operates at speeds up to 20MHz to deliver four times the performance of previous 16bit cores. Average performance levels of up to 12.25MIPS at a power consumption of 75mW mean this core can also provide the industry's lowest power/MIPS ratio.

A key element in achieving the core's performance levels are four general purpose register banks, for fast context switching and improved real time control, and an eight channel dma controller that can transfer data at up to 18Mbyte/s. In the case of the TMP94FD53, the device also helps to minimise external memory requirements through 128kbyte of on board rom and 512kbyte of on board flash, which is connected to the cpu core via a 32bit data bus. The microcontroller also incorporates an on board CAN controller, which offers full CAN2.0B functionality, ensuring compatibility with both standard frame and extended frame identifiers. Finally, for further compatibility with Bluetooth automotive designs, the microcontroller also offers the integrated timer and UART capabilities demanded by the Bluetooth stack.

Porting the Bluetooth stack and the serial profile to the TMP94FD53 requires 25kbyte and 3kbyte of rom respectively. As a result, there is significant spare on board rom for application specific storage requirements. In addition, depending on application, it is estimated that the cpu load for the implementation is just 0.2MIPS and that the ram requirement for data and stack is around 1kbyte.

To help designers to speed the development of Bluetooth based applications, a demonstration system has been developed that uses technology from Toshiba and IAR. This system comprises a Toshiba TLCS-900-H2 microprocessor prototyping board and Bluetooth Starter Kit hardware from IAR Systems. The schematic of the development system (Figure 2) shows the development system a TMP94FD53 target running an OSEK rtos and featuring the embedded 'upper layer' Bluetooth protocol stack connects, via the uart interface to the Bluetooth module on IAR's Starter Kit. The Starter Kit design consists of a main board, a 'plug in' Bluetooth daughter board and an onboard antenna, plus all relevant software and documentation. The software includes a sample Bluetooth application. During development and testing, the Starter Kit can communicate with a second kit linked to a pc, simulating the behaviour of the local Bluetooth device.

It is anticipated that demand for Bluetooth systems will grow rapidly in the coming years and, in order to address this demand, automotive engineers will be under increasing pressure to implement Bluetooth functionality. Choosing microcontrollers such as Toshiba's TMP94FD53 or TMP92FD54, which are suited to high performance automotive applications, and optimised versions of the highly efficient Bluetooth stack from IAR Systems, will help the designer to provide such functionality while addressing ongoing pressures to reduce design cycle times, lower component counts and minimise overall cost.

Author
Graham Pitcher

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