fixing_strings (#1)

Reviewed-on: #1
Co-authored-by: Edward Wall <edward.wall@psi.ch>
Co-committed-by: Edward Wall <edward.wall@psi.ch>

Makefile

@@ -1,7 +1,12 @@
 include /ioc/tools/driver.makefile
 
-BUILDCLASSES+=Linux
+MODULE=sinqS7plcFW
+BUILDCLASSES=Linux
+EPICS_VERSIONS=7.0.7
+ARCH_FILTER=RHEL%
 
 DBDS += s7plcFWBase.dbd
 DBDS_3.14 += s7plcFWCalcout.dbd
 DBDS_3.14 += s7plcFWReg.dbd
+
+USR_CFLAGS += -Wall -Wextra -Wunused-result

README.md

@@ -0,0 +1,13 @@
+# SinqS7PLCFW
+
+This is a fork of Dirk Zimoch's [epics\_driver\_modules/s7plcFW](https://git.psi.ch/epics_driver_modules/s7plcFW), with the following adjustments:
+
+* The String offset, now takes the two prefix bytes (max string length, current
+  string length) into account, so you don't have to add 2 to each offset in
+  order for the driver to read the correct string
+* The length of a String read from the SPS and written to the Val field of a
+  stringin record is no longer static, but instead read from the SPS directly,
+  to avoid having bytes leftover in the buffer from a previous string.
+* The Makefile has been slightly adjusted, limiting the build targets.
+
+The default driver behaviour is documented in the file [s7plcFW.html](./s7plcFW.html).

devS7plcFW.c

@@ -2033,7 +2033,11 @@ STATIC long s7plcFWInitRecordStringin(stringinRecord *record)
 
 STATIC long s7plcFWReadStringin(stringinRecord *record)
 {
+    // The SPS includes the max length of the string and the length of the
+    // current string, as the first two bytes in the register.
+
     int status;
+    epicsUInt8 uval8;
     S7memPrivate_t *priv = (S7memPrivate_t *)record->dpvt;
 
     if (!priv)
@@ -2044,11 +2048,18 @@ STATIC long s7plcFWReadStringin(stringinRecord *record)
         return -1;
     }
     assert(priv->station);
+
+    status = s7plcFWRead(priv->station, priv->offs+1,
+        1, &uval8);
+    s7plcFWDebugLog(3, "stringin %s: read 8bit %02x\n",
+        record->name, uval8);
+    uval8 = uval8 <= priv->dlen ? uval8 : priv->dlen;
+
     memset(record->val, 0, priv->dlen);
-    status = s7plcFWReadArray(priv->station, priv->offs,
-                1, priv->dlen, record->val);
+    status = s7plcFWReadArray(priv->station, priv->offs+2,
+                1, uval8, record->val);
     s7plcFWDebugLog(3, "stringin %s: read array of %d 8bit values\n",
-        record->name, priv->dlen);
+        record->name, uval8);
     if (record->val[priv->dlen] && !memchr(record->val, 0, priv->dlen))
     {
         /* truncate oversize string */