[hpsdr] Blackfin 32*32 bits multiply

[Robert M. Ganter HB9DNN]

Hello Greg and list,

I fully agree with You about the bit width requirements for audio 
applications.
I'd like to put a question mark, however, to the following:

> The Blackfin looks like a great 16-bit DSP, but for
> high resolution audio work (or baseband SDR using
> 24-bit converters) I think a better choice would be a
> DSP that has native 32-bit arithmetic.

The Blackfin is more than a 16bit DSP. It is a DSP and a 
microcontroller. Although only 16bit it is possible (as with any decent 
processor) to do higher precision calculation at higher (time-)costs. 
Anyone remember the DEC PDP-11? The "lower cost" versions used 4bit 
hardware (TTL 74xx series), the architecture was actually simulated in 
microcode. Same for the HP48 calculator, 4bit CPU, everything else is SW.

IMHO we should look at the whole *system*, not just the DSP.

I'd therefore ask the following questions:
- What are the requirements needed for an SDR with two 24bit/192kSPS 
input data streams (MMACs/s, memory for data, coefficients, etc.)
- Is 32bit hardware needed or could it be done with 16bit hardware and 
libraries?
- Fixed point <-> floating point? I'd go for fixed point, but there 
might be arguments for floating point
- One chip DSP/uController <-> two chip solution with dedicated DSP and 
uController.
- Development environment. The best DSP/Microcontroller does not help if 
the development tools cost a fortune. Remember, this is amateur radio 
and it is unlikely that any of us would spend several k$ for tools. Even 
if somebody has access to such tools there is no way for others to 
change (edit/recompile, etc) anything later.
- What should/ could be done in an FPGA, what in a DSP?
- What should/could be moved to a PC, is standalone operation (i.e. no 
PC at all) an option?

There are certainly more questions to be asked, this is just what came 
across in a quarter of an hour.

There are not many off the shelf DSPs avaliable which are inexpensive 
and which have inexpensive or even free development tools.
If the Blackfin is able to do the job (computing power) it might be well 
worth using it:
- DSP/uController
- glueless memory controller for Flash/SDRAM
- synchronous serial ports, up to 32bit word width
- parallel port interface. Might be an alternative to the serial ports 
to interface to an FPGA
- 10/100MBit Ethernet MAC
- full development environment with uCLinux

As with many other modern DSPs/uControllers (and also most FPGAs) the 
Blackfin is only available in a tiny 0.8mm fine pitch BGA. Maybe a small 
module containing everything needed for the DSP and with "amateur 
friendly" connectors will be needed.

vy 73

Robert HB9DNN


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