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PIXELCONFIG_BPC_DIFF.md

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PixelConfig vs on-disk BPC (SERVAL vs file)

This note explains what the PixelConfig refresh and PixelConfigDiff waveform represent, and how they relate to mask / BPC PVs. It is aimed at operators and integrators debugging “chip programmed differently than my file.”

Two different things

Source Meaning
SERVAL PixelConfig (per chip) The current 65536-byte pixel configuration SERVAL holds for that chip—what the detector is actually using after loads, applies, and API updates.
On-disk .bpc file The file the IOC reads using BPCFilePath + BPCFileName. Used for mask editing, upload, and this comparison.

They can differ if, for example: the file was edited on disk but not uploaded; ApplyConfig / WriteData was not run; another client changed SERVAL; or the IOC points at a different path than you expect.

The driver does not guess which side is “correct”; it reports equality or byte differences.

What “Refresh PixelConfig” does

  1. Reads the on-disk BPC into memory (same read path as other mask/BPC operations).
  2. For each chip i, GET /detector/chips/<i>/PixelConfig, parse JSON, base64-decode to bytes.
  3. Compares decoded bytes to file bytes at offset i × 65536 for up to 65536 bytes per chip (quad file = 262144 bytes total).
  4. Updates per-chip status PVs and fills PixelConfigDiff.

Match codes (PixelConfigMatchBPC_RBV)

Code Meaning
-1 Error (HTTP, JSON, decode, etc.)
0 Bytes differ (PixelConfigMismatchBytes_RBV = count of differing byte positions in the compared range)
1 Compared range matches
2 No BPC file (or empty read)
3 Length / size mismatch (decoded length vs expected chip slice)

Waveform indexing: BPC vs MaskBPC vs PixelConfigDiff

  • BPC PV (TPX3_BPC_PEL): Linear file order—index k is byte k in the .bpc file.
  • PixelConfigDiff: Image order = j × cols + i (same row-major convention as maskCircle / mask write), sample (i, j) = abs(SERVAL[k] − BPC[k]) where k = pelIndex(i, j). That is the same mapping used when a mask is written into the .bpc file (pelIndex in mask_io.cpp). DetOrient / TPX3_DET_ORIENTATION is included in pelIndex, so rotated layouts match the mask editor.
  • MaskBPC when read from disk (“read from bpc” / MaskPel): fills value[j*COLS+i] from bufBPC[pelIndex(i, j)], same as mask write and PixelConfigDiff (no bcp2ImgIndex on this path).

PixelConfigDiff values

Each element is abs(byte_SERVAL − byte_BPC) for the same logical pel after mapping. Bit-level mask changes (e.g. bit 0) typically show as small integers (often 1) where that byte differs.

Related PVs and UI

  • RefreshPixelConfig: Dashboard.template; forward-links to PixelConfigDiff.PROC so the waveform record processes after the driver updates the buffer.
  • Phoebus: tpx3App/op/bob/Mask/PixelConfigMaskPanel.bob (embedded from Mask.bob).

Release history

See RELEASE.md, section R1-6-2, for implementation details (asyn array type, callback length, bcp2ImgIndex chip-index fix, pelIndex-based PixelConfigDiff).