1. Configuration
1.1. Compute Units to be registered (file cacaovars.bash)
To enable zonal filtering, the following compute units must be enabled:
CACAO_FPSPROC_ZONALFILTERING: Perform zonal filteringCACAO_FPSPROC_MVMGPU_DM2MVAL: zonal to modal space translation of filtered output
The cacaovars.bash entries for enabling predictive control are:
export CACAO_FPSPROC_ZONALFILTERING="ON"
export CACAO_FPSPROC_MVMGPU_DM2MVAL="ON"
1.2. Turning zonal filtering on/off
The zonal filtering (ZF) compute unit inserts itself between the mvalC2dm and DMch2disp compute units. Without ZF, mvalC2dm writes to stream aol_dmC. With ZF, mvalC2dm is reconfigured to write to stream aol_zvalDM, and compute unit zfilt takes aol_zvalDM as input and writes to aol_dmC.
To switch ZF on/off:
cacao-aorun-zonalfiltering on
cacao-aorun-zonalfiltering off
2. Modal Feedback
Modal feedback is essential to AO loop stability when performing zonal filtering.
Without modal feedback, zonal filtering creates a discrepancy between the actual state of the DM correction and its modal representation aol_modevalDM. For example, when performing trunction of the command in zonal space, the modal control loop is unaware of the trunction, and can keep “pushing” the command beyond the trunction, creating a growing discrepancy between the modal representation and the actual DM correction. It is difficult for the control loop to recover from this discrancy.
The figure below and corresponding video show such instability when implementing zonal trunction of the output command. Notice how the loop becomes unstable once trunction occurs.
With modal feedback implemented, the mval2dm converts the truncated zonal command back into modal space (stream aol_modevalDMf) at each loop interation. The mfilt compute unit detects that aol_modevalDMf has been updated, and uses it to uptdate its own internal DM correction state in modal space. The control loop is then aware of the truncation, avoiding loop instability. Compare the figure and video below (with modal feedback) from the one above.
