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Altera_Forum's avatar
Altera_Forum
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16 years ago

Help with Efficient Conversion?

I am looking to convert a 16bit number(X) to another 16 bit number(Y). X is a count coming from a Tach output on a Fan. Y is the fan's corresponding RPM. (note: this is a inverse relationship)

The relationship is Y = 60 / (X*1.706e-6)

To keep it fixed point so far the best I have come up with is 2 divides:

First I = X / 58 (I is intermedite value) then take 606000 / I to get Y.

X ranges from about 5858 to 30000.

I am worried about the real estate of 2 divides, since I will need 8 channels of this (8x2=16 divides) on my cyclone II.

Any help improving this calculation? Thanks!

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    How often do you need a result? If you need this result several million times a second, yes, I'd worry about the area. If it's once per millisecond, then don't use the LPM_DIVIDE, but write a tail divider that gives a result once per 32 clock cycles or so.

    Best regards,

    Ben
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    if the clock rate is much higher than the sample rate, you can TDM or channelize your arithmetic to save resources

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    I you want exactly a calculation of the given expression, I would calculate 35294118/X, using an serial divider.