database: forward rate limit to FrameRate.DRVH.

Both AcquirePeriod and FrameRate can be used to define frame rate. Keep
their limits consistent by forwarding the inverse of period limit to the
FrameRate record.

To keep backward compatibility, the frame rate is computed based on the
value of the AcquirePeriod.DRVL. Changing that at runtime requires
reprocessing AcquirePeriodLimitFwd to forward to FrameRate.DRVH.

CameraApp/Db/limits.db

@@ -2,6 +2,25 @@ record(bo, "$(P)$(R)FrameRateEnable") {
    field(VAL, 1)
 }
 
+record(calc, $(P)$(R)FrameRateLimit) {
+   field(DESC, "Compute frame rate limit from period")
+   field(INPA, "$(P)$(R)AcquirePeriod.DRVL")
+   field(CALC, "1 / A")
+   field(FLNK, "$(P)$(R)FrameRateLimitFwd")
+}
+
+record(ao, "$(P)$(R)FrameRateLimitFwd") {
+   field(DESC, "Forward limit to FrameRate.DRVH")
+   field(PINI, "YES")
+   field(OMSL, "closed_loop")
+   field(DOL, "$(P)$(R)FrameRateLimit PP")
+   field(OUT, "$(P)$(R)FrameRate.DRVH NPP")
+}
+
+record(ao, "$(P)$(R)FrameRate") {
+   field(DRVL, "0")
+}
+
 record(ao, "$(P)$(R)AcquirePeriod") {
    field(DRVL, "$(ACQUIRE_PERIOD_DRVL=0)")
    field(DRVH, "inf")