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Re: [AVR-Chat] µMFPU

2008-01-24 by np np

FPU's in microcontrollers !

I had to write my own FPU's in days gone by.

Programming is so easy these days !

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----- Original Message ----
From: "BobGardner@aol.com" <BobGardner@aol.com>
To: AVR-Chat@yahoogroups.com
Sent: Thursday, 24 January, 2008 3:28:31 AM
Subject: Re: [AVR-Chat] µMFPU

Has anyone timed how long it takes to multiply and add floating point 
numbers in a loop? I can do 50,000 fp mults or fp adds with a 16mhz avr, so it has 
to be faster than that to be a performance win.

In a message dated 1/23/2008 10:17:39 P.M. Eastern Standard Time, 
tjkeller1@windstrea m.net writes:

Juistb discoverd this chip, an 18 pin DIP (also available in SMD 
packaging) which provides a very powerful FPU + other functions, 
including 2 12 bit ADCs, a full RS-232 port (including level shifting), 
string processing, NMEA string parsing, numeric to string and string to 
numeric as well as numeric format conversions (8, 16, 32 bit int back 
and forth, as well as IEEE 754 FP back and forth). Costs are $19.95 
qty 1 (Sparkfun), $13.95 qty 100. 

http://www.micromeg acorp.com/ umfpu-v3. html fior technical information.

Offers both SPI (15 Mhz) and I2C (400 Khz) interface, ~~ 30 Mhz 
operation (without ANY external components, you can add an external 
crystal/cap network to boost speed a little, apparently).

Not exactly inexpensive, but not badly priced for all it will do.

Thought you guys would like to know about this, in case you didn't 
already know.

avrFreak

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Re: [AVR-Chat] µMFPU

2008-01-24 by Tom Becker

> ... I can do 50,000 fp mults or fp adds with a 16mhz avr...

FWIW, I did some Kalman work with the µMFPU v3.1 on a ZX-24 last year 
and found it is very useful - and fast if you keep your work on the FPU, 
i.e. keeping vars on the FPU and using user-defined functions instead of 
single FPU instructions (which would need to transfer data both ways).  
50,000 32-bit float multiplies per second sounds pretty fast, but try to 
do a 3x3 multiplicitive matrix inversion, something of a benchmark.

Although the FPU now offers a single instruction for small matrix 
inversions (it did not when I did this work), I wrote what was 
apparently the quickest FPU code to do that then, in 465µS.  The new 
instruction is faster.

Here is µMFPU v3.1 function code that executes a 3x3 inversion.  How 
fast can a 16MHz AVR do this?

' F0=1/(MB3a*MA3a)-(-MB3d*MA3b)+(MB3g*MA3c) '1/determinant sum of 3 
cofactors
 #asm
 left
 fset, 14
 fmul, 5
 fmac, 17, 6
 fmac, 20, 7
 finv
 right
 #endasm




Tom