Video and Vision Processing Suite Intel® FPGA IP User Guide

ID 683329
Date 4/04/2022

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18.2.1. Updating Scaler IP Runtime Coefficients

If you select polyphase and turn on runtime coefficient updates, you can edit the values in the horizontal and vertical scaling coefficient memories at any time via the Avalon memory-mapped agent interface.

To minimize the implementation cost of the coefficient memories, you cannot directly access the value of each coefficient through a single read or write to the register map. You must write the values for the coefficients in a given phase (vertical or horizontal) to a set of addresses in the register map. Then declare through separate addresses which phase and which bank the IP writes the coefficients to.

  1. Write the values of the coefficients for one phase to the RT_COEFF_LOAD_TAP_Xregisters (0 <= X < 64, addresses 0x020C to 0x0308). The IP has 64 addresses into which you may write new coefficients. If the coefficient phase you are updating only has coefficients for N taps (where N < 64), you need only write values to the first N addresses in this range.
  2. Write the index of the bank to which the IP should write this phase of coefficients to the RT_COEFF_LOAD_BANK_SELECT register (address 0x0200).
  3. Write the index of the phase to which the IP should write the coefficients to the RT_COEFF_LOAD_PHASE_SELECT register (address 0x0204).
  4. Write to the RT_COEFF_LOAD_COMMIT register (address 0x208) to commit the new coefficients to the specified phase in the specified bank. Write 1 to this register if it is a horizontal scaling filter coefficient phase, and 0 if it is a vertical scaling filter coefficient phase.

You must repeat this process for every phase in every bank that you want to update. Unlike updates to settings registers (such as the output field width), coefficient updates take immediate effect. The IP does not hold them until a frame boundary. To avoid the IP updating coefficients in the middle of a frame, Intel recommends using at least two banks of coefficients. This way the software controlling the system can make updates to the coefficients in one bank, while the scaler reads coefficients for processing from the other bank. When the coefficient updates are complete, the software can swap the coefficient read bank to the newly updated bank by updating the value in the H_BANK or V_BANK address in the register map. These registers are standard settings registers, so the update to the coefficient read bank only takes effect at a frame boundary.