why readback only in 24.0 format?
Why is it not possible to readback values in 28.0 format? I think this would be very useful!!!
For example I would like to monitor the value that is fed to a index selected mux. As far as I can see this input is in 28.0 format. When I use the readback cell I can only select 24.0 format as a maximum. So I always see 0.0000000.
A similar problem is monitoring te AUX ADC value. Here I'd like to monitor the value to calculate the divider that is needed to feed a lookuptable which in turn feeds a "sigle slew ext vol". This is to control volume with predefined steps and range using an ext. pot.
Regards
Bernd
Audio Signal Processors
SigmaDSP Audio Processors
adau1701
readback
Hello Bernd,
Depending on the SigmaDSP that you are using, the bit depth of the readback cell will vary.
Generation 2 SigmaDSPs like the AD1940 and ADAU1701 families have a hardware DSP readback function. The corresponding hardware trap register was designed only with 24 bits of resolution. So, in this case, your resolution is limited. It's a bit of a pain, but if you really need the full resolution range, you can put a few linear gain stages before the readback cell (gain > 1) and then a few gain stages afterwards (gain < 1) to achieve a net gain of 1. You could then see the values of the LSBs (although they would be scaled accordingly). This requires extra instruction cycles, but should help you to accomplish what you want in your design.
Realizing that this hardware readback function was a limitation in our Generation 2 devices, we revised the design in the Generation 3 devices (ADAU1761, ADAU144x, etc...). The Generation 3 readback function is implemented in software and has a full 28 bit resolution, allowing the user to read all bits in either 28.0 or 5.23 format.
Best Regards,
Brett
Can the software readback be added to the earlier chips?
Hi J3627:
No, there are no plans to have full word read back on earlier versions of the SigmaDSP but like Brett mentions, here, there are workarounds for this limitation. The only drawback is that they will cost you one or two extra instructions.
>> Here I'd like to monitor the value to calculate the divider that is needed to feed a lookuptable which in turn feeds a "sigle slew ext vol". This is to control volume with predefined steps and range using an ext. pot.
Hi BerndH:
My suggestion for what you are trying to do is to use a lookup table (even an interpolated one or log one) to write your pre-divided set of values in the DSP. The process you are describing sounds complicated and uC intensive. As a matter of fact, I believe there are some threads in the Forum that show how to use an Aux ADC paired with a lookup table followed by an index selectable volume control to control potentiometer taper.
Regards
Miguel
Hi J3627,
The limitation is in hardware, not software. Unfortunately, there is no software workaround other than the one I mentioned.
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