fixed point digital low pass filters

The first order filter is just the first order filter. It can't be worth butter or anything.

these

Probably even MSP430 or 68HCS12 could be sufficient.

The real question is what are you trying to accomplish by this filtering. A first order corner at 100kHz at a sample rate of 250kHz doesn't seem to make much sense.

It is certainly possible, however I don't know if you can :)

What a horrid code.

VLV

IIRC both of these processors top out at about 40MHz clock speed. So you're saying he can run six second-order, 32-bit precision filters in

Interesting.

One can make this conversion with proper guidance; I don't know if anyone could with Vladimir as his only source of information.

And thank you for increasing world knowledge by saying why.

I find it odd that your corner frequency is only 80% of your Nyquist rate. You really aren't going to be achieving much by filtering this data.

Perhaps you should go over exactly what you're planning to achieve, and with what data.

This is going to consume a lot of clock ticks on either a microprocessor or a DSP chip. Expect to need to use 32-bit arithmetic (or 24, if you like old Motorola DSP chips). Plan on benchmarking this, and don't expect to do it on a cruddy old PIC.

Yes you can. Search around on the web, see if you can find an article about fixed-point or fractional arithmetic. All the processors that I've used support some sort of fractional arithmetic, at least indirectly -- DSP chips support it directly, and 'regular' processors support it by coughing up both (or selectable) parts of the double-precision result you get when multiplying two single-precision numbers (I.e. if the processor is a 16-bit one, an integer multiply will either fill two registers with the high and low parts, or there will be two integer multiplies, one for each part).

Otherwise Really Fast Processors can take multiple clock ticks to do multiplication (never mind divide), so remember to benchmark or count clock ticks when you investigate doing this in fractional arithmetic.

This is _not_ the best code, although I presume it works. Here again, you could do well to search the web for IIR filter information. I'd suggest you think about getting a copy of "Understanding Digital Signal Processing" by Rick Lyons as well -- there's a whole chapter on choosing which IIR filter is the right one in what circumstance.