18.3.3. FIR Coefficient Specification
The IP requires you to define a fixed-point type for the coefficients. The user-entered coefficients (shown as white boxes in the parameter editor) are rounded to fit in the chosen coefficient fixed-point type (shown as purple boxes in the parameter editor).
- For run-time editable coefficients, you must enter the desired coefficient values through an Avalon memory-mapped agent control interface at run time, and you can update the coefficient values as often as once per frame.
Note: Without enabling the coefficient initialization file, the coefficient values all revert to undefined after every reset, so you must initialize coefficients at least once on start-up.
- To keep the register map as small as possible and to reduce complexity in the hardware, the IP reduces the number of coefficients that it edits at run time when you turn on any of the symmetric modes.
- For T unique coefficient values after symmetry, the register map contains T addresses into which you should write coefficients, starting at address 7 and finishing at T+ 6.
For fixed coefficients, you specify the values for the coefficients with a comma-separated .csv text file. The selected coefficient values take effect immediate effect at reset.
Regardless of the symmetry mode, the text file must contain a full listing of all the coefficients in the N×M array i.e. the file must always contain N×M comma-separated values. When the .csv file is parsed in Platform Designer to create the list of compile time coefficients, the IP checks the values entered against the selected symmetry mode and provides warnings if the coefficients are not symmetric across the selected axes. The values specified in the .csv file must be in their unquantized format. For example, if you want a value of 1.7 for a given coefficient, the value in the file should be 1.75. When the file is parsed in Platform Designer, the coefficients automatically quantize according to the precision you specify.
Run-time Editable Coefficients
To keep the register map as small as possible and to reduce complexity in the hardware, the number of coefficients that are edited at run time is reduced when you turn on any of the symmetric modes.
If the IP has T unique coefficient values after symmetry, the register map contains T addresses into which you should write coefficients, starting at address 0x200 and finishing at 0x200 + (4*(T-1)).
Write coefficient index 0 (as described in the symmetry section) to address 0x200. Then write each successively indexed coefficient at each following address. The updated coefficient set takes effect immediately. To avoid the IP updating coefficients in the middle of a frame, Intel recommends reading bit 3 of the status register to check that the algorithmic core is idle before writing new coefficients.