[ Home | Up | Disclaimer ]


8-Bit Roundup: Sprow ARM7TDMI Coprocessor

Published in Drag 'n Drop, volume 1, issue 01 (October 2009), pp.29–30. Reproduced by kind permission of Chris Dewhurst.

[Pack shot]

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.

[Screen shot]

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.

Systems BBC Micro
Price £87.50
Delivery Free

[Bird's eye view]


Processor OKI microcontroller with ARM7TDMI core at 64 MHz, 8 KB unified cache
Memory 16 MB SDRAM, expandable to 64 MB
512 KB internal Flash ROM, space for 4 MB external Flash
Optional serial EEPROM
Interface Acorn Tube®, via header pins or 40-way IDC
Optional RS 232 serial link
Power consumption 180 mA at +5V
Addendum (January 2020): I subsequently discovered that both upgrade failures were caused solely by bugs in the unusual filing system fitted to my BBC Micro, exercised by the ARM7TDMI coprocessor's use of files and machine addresses larger than 64 KiB. I have since fixed these bugs, which are unlikely to occur in the official Acorn firmware. That said, my advice to verify the integrity of the upgrade image still stands.

Warning: You are using this Web site at your own risk. The author of the files contained herein accepts no liability for any loss, injury or death, of any nature and howsoever caused, arising directly or indirectly from the use of, or failure, inability, or unwillingness to use, this Web site or the files contained herein. The aforementioned author accepts neither responsibilty nor liability for the content of linked Internet sites.

Greg Cook, [email address] Last updated 11 January 2020

Valid HTML 4.01 Strict. Hosting by NetNorth

[ Top of page ]