Index: trunk/psphot/src/psphotStackImageLoop.c
===================================================================
--- trunk/psphot/src/psphotStackImageLoop.c	(revision 27547)
+++ trunk/psphot/src/psphotStackImageLoop.c	(revision 27657)
@@ -7,5 +7,5 @@
 }
 
-bool psphotImageLoop (pmConfig *config) {
+bool psphotStackImageLoop (pmConfig *config) {
 
     bool status;
@@ -14,4 +14,10 @@
     pmReadout *readout;
 
+    pmFPAfile *input = psMetadataLookupPtr (&status, config->files, "PSPHOT.INPUT");
+    if (!status) {
+        psError(PSPHOT_ERR_PROG, false, "Can't find input data!");
+        return false;
+    }
+
     pmFPAview *view = pmFPAviewAlloc (0);
 
@@ -19,6 +25,44 @@
     if (!pmFPAfileIOChecks (config, view, PM_FPA_BEFORE)) ESCAPE ("failed input for fpa in psphot.");
 
-    // XXX for now, we assume there is only a single chip in the PHU:
-    psphotStackReadout (config, view);
+    // for psphot, we force data to be read at the chip level
+    while ((chip = pmFPAviewNextChip (view, input->fpa, 1)) != NULL) {
+        psLogMsg ("psphot", 4, "Chip %d: %x %x\n", view->chip, chip->file_exists, chip->process);
+        if (! chip->process || ! chip->file_exists) { continue; }
+        if (!pmFPAfileIOChecks (config, view, PM_FPA_BEFORE)) ESCAPE ("failed input for Chip in psphotStack.");
+
+        // there is now only a single chip (multiple readouts?). loop over it and process
+        while ((cell = pmFPAviewNextCell (view, input->fpa, 1)) != NULL) {
+            psLogMsg ("psphot", 5, "Cell %d: %x %x\n", view->cell, cell->file_exists, cell->process);
+	    if (!pmFPAfileIOChecks (config, view, PM_FPA_BEFORE)) ESCAPE ("failed input for Cell in psphotStack.");
+
+            // process each of the readouts
+            while ((readout = pmFPAviewNextReadout (view, input->fpa, 1)) != NULL) {
+                psLogMsg ("psphot", 6, "Readout %d: %x %x\n", view->readout, cell->file_exists, cell->process);
+                if (! readout->data_exists) { continue; }
+
+		// XXX for now, we assume there is only a single chip in the PHU:
+		if (!psphotStackReadout (config, view)) {
+                    psError(psErrorCodeLast(), false, "failure in psphotReadout for chip %d, cell %d, readout %d\n", view->chip, view->cell, view->readout);
+                    psFree (view);
+                    return false;
+		}
+
+	    }
+	    // drop all versions of the internal files
+	    status = true;
+	    status &= pmFPAfileDropInternal (config->files, "PSPHOT.BACKMDL");
+	    status &= pmFPAfileDropInternal (config->files, "PSPHOT.BACKMDL.STDEV");
+	    status &= pmFPAfileDropInternal (config->files, "PSPHOT.BACKGND");
+	    if (!status) {
+		psError(PSPHOT_ERR_PROG, false, "trouble dropping internal files");
+		psFree (view);
+		return false;
+	    }
+	}
+	// save output which is saved at the chip level
+	if (!pmFPAfileIOChecks (config, view, PM_FPA_AFTER)) ESCAPE ("failed output for Chip in psphot.");
+    }
+    // save output which is saved at the fpa level
+    if (!pmFPAfileIOChecks (config, view, PM_FPA_AFTER)) ESCAPE ("failed ouput for FPA in psphot.");
 
     // fail if we failed to handle an error
@@ -32,4 +76,4 @@
    the easiest way to implement this is to assume we can pre-load the full set of images up front.
    with 5 filters and 6000^2 (image, mask, var = 10 byte per pixel), we need 1.8GB, which is not too bad.
- */
+*/