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8-Bit Roundup: Sprow ARM7TDMI Coprocessor

SINCE 2004 there has been a steady trickle of new hardware designed to plug into the BBC Micro, Master and Electron. Produced for the Internet market by individuals and small teams, the typically well-built devices add desirable new capabilities to these already versatile machines.

The ARM7TDMI Coprocessor by Sprow (Robert Sprowson) is no exception. Released in 2005, this neat board brings the highly successful ARM architecture back to its first application, an Acorn Tube client, revisiting Acorn’s 1985 ARM Evaluation System.

The coprocessor arrives as a slim, pre-assembled PCB in simple packaging, with a comprehensive sixteen-page user guide and a welcome note. An internal model fits inside the Master while the external version, requiring its own power source, connects to any suitable BBC series computer. When powered-up the coprocessor then takes control, while the host provides the display, keyboard and I/O facilities. The gateway between the two is Sprow’s FPGA reconstruction of Acorn’s Tube ULA.

The change of personality is astonishing. The built-in ARM BASIC V runs properly-coded BASIC II programs up to 200 times faster, in almost 16 MB of workspace, though the host’s unimproved capacity restrains many I/O-intensive programs.

For advanced users, Sprow’s website carries programming documentation and also firmware upgrades, which can disable the unit if they go wrong: although Sprow has helpfully recovered mine twice, future upgrades will be safer if they verify their integrity – a straightforward CRC calculation – before proceeding.

The firmware itself, the ARM Tube OS, replicates not much more of the RISC OS environment than BASIC needs to run, but Sprow welcomes enquiries about any particular absent feature. The ARM7TDMI Coprocessor’s advantage thus lies in the twenty years of improvements in IC technology. Nearly all its applications are in BASIC, embracing the speed and memory increases provided by modern silicon. However, four years on there is still a dearth of native software for this platform, and sadly today’s cores no longer fully support ARM1 code.

Any BBC Micro enthusiast who wants a boost for their BASIC library, or would like to try ARM coding in a familiar environment, will find this unit a solid if slightly pricey solution.

The ARM7TDMI Coprocessor is available for £87.50 inc. p&p from Robert Sprowson.

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Greg Cook,
http://regregex.bbcmicro.net/pub/arm7tdmi.htm Last updated 11 January 2020

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