Copy of old lessons from afs webpage

caLesson1/caLesson1.c

@@ -0,0 +1,171 @@
+/* caLesson1.c
+   by Dirk Zimoch, 2007
+   
+   This is a very simple channel access client program.
+   It uses the EPICS R3.13 channel access functions
+   but can as well run with EPICS 3.14.
+*/
+
+#include <stdio.h>
+
+/* include EPICS headers */
+#include <cadef.h>
+
+/*
+#define WITH_NOT_EXISTING_CHANNEL
+*/
+
+/* Strings describing the connection status of a channel */
+const char *channel_state_str[4] = {
+    "not found",
+    "connection lost",
+    "connected",
+    "closed"
+};
+
+int main ()
+{
+    chid beamcurrentID;
+    double beamcurrent;
+
+    chid gapID;
+    double gap;
+
+#ifdef WITH_NOT_EXISTING_CHANNEL
+    chid doesnotexistID;
+    double doesnotexist;
+#endif
+
+    int status;
+    
+    
+    /* Step1: initialize channel access and search for all channels. */
+    ca_task_initialize();
+    
+    /* Assign channel names to channel IDs. */
+    ca_search ("ARIDI-PCT:CURRENT", &beamcurrentID);
+#ifdef WITH_NOT_EXISTING_CHANNEL
+    ca_search ("doesnotexist", &doesnotexistID);
+#endif
+    ca_search ("X10SA-ID-GAP:READ", &gapID);
+    /* Nothing has been sent to the network so far! */
+    
+    /* Send all requests in parallel, wait for maximal 5.0 seconds. */
+    printf ("searching ...\n");
+    status = ca_pend_io(5.0);
+    
+    /* This ca_pend_io() is a very expensive action in terms of network
+       bandwidth because UDP broadcasts are sent to all IOCs in the subnet.
+
+       For every broadcast, each IOC has to check if it owns one of the
+       requested channels. If no IOC replies, the boradcast request
+       is repeated up to 100 times.
+       Do not search for obsolete channels! If channels have been
+       removed, also remove them from your clients to reduce unnecessary
+       broadcast traffic. Check the spelling of channel names if
+       channels don't connect.
+       
+       One broadcast package can contain many channel requests. This
+       is much more efficient than sending only one request at a time.
+       Thus, always try to connect all channels at once, using only
+       one ca_pend_io() after all ca_search() calls. This also speeds up
+       your program: waiting 10 seconds for 1000 channels in parallel
+       is much shorter than even waiting only 1 second for 1000 sequential
+       channel searches. ca_pend_io() returns early when all channels are
+       found.
+    */
+    
+    /* Check for errors */
+    switch (status)
+    {
+        case ECA_NORMAL:
+            printf ("all channels found\n");
+            break;
+        case ECA_TIMEOUT:
+            printf ("some channels not found yet\n");
+            break;
+        default:
+            printf ("unexpected error while searching: %s\n",
+                ca_message(status));
+    }
+    /* If not all channels can be found now, the IOC is probably down.
+       Searching continues in the background and channels connect
+       automatically when the IOC comes up.
+       
+       Try to uncomment the #define WITH_NOT_EXISTING_CHANNEL above to
+       see what happens if a channel cannot be found.       
+       
+       Normally, ca_search() should not be called any more after startup.
+       There may be exceptions, when channels are added dynamically to a
+       running program. But this is not the normal case.
+
+       Connected channels may disconnect and reconnect later automatically
+       when an IOC reboots. Always keep this in mind when doing any
+       network traffic. Any long-lived program, such as GUIs or servers,
+       MUST be written in a way to survive disconnected channels and
+       they MUST react in a reasonable manner.
+       
+       It depends on the application and is generally is your problem what
+       "reasonable" means. 
+    */
+    
+    /* Step 2: do channel access data transfer. */
+    ca_get(DBR_DOUBLE, beamcurrentID, &beamcurrent);
+#ifdef WITH_NOT_EXISTING_CHANNEL
+    ca_get(DBR_DOUBLE, doesnotexistID, &doesnotexist);
+#endif
+    ca_get(DBR_DOUBLE, gapID, &gap);
+    /* Nothing has been sent to the network so far! */
+
+    /* Send all request in parallel, wait for maximal 1.0 second. */
+    printf ("reading ...\n");
+    status = ca_pend_io(1.0);
+    
+    /* As before, it increases network performance to do as many ca_get()
+       calls as possible with one ca_pend_io(). In opposite to searching,
+       data transfer is done via TCP. Thus, it affects only the client
+       and the IOC and all network components in between. It does not
+       affect all IOCs on the same network as searching does! But still,
+       many requests can be sent in the same message if they go to the
+       same IOC -- which is often the case. Luckily, you don't have to
+       care about this. Just always try to read as many channels as
+       possible in parallel.    
+    */
+    
+    switch (status)
+    {
+        case ECA_NORMAL:
+            printf ("all values received\n");
+            break;
+        case ECA_TIMEOUT:
+            printf ("some values not received\n");
+            break;
+        default:
+            printf ("unexpected error while reading: %s\n",
+                ca_message(status));
+    }
+    
+    /* Print values of all channels but inform the user
+       if a channel is connected or not. The value of a
+       not connected channel is not valid, of course.
+       Never take such a value for serious!
+       Always when the result of ca_pend_io() after ca_get()
+       is not ECA_NORMAL, you MUST check ca_state() of all
+       involved channels before trusting any value.
+    */
+    printf ("Beam current (%s): %g\n",
+        channel_state_str[ca_state(beamcurrentID)],
+        beamcurrent);
+#ifdef WITH_NOT_EXISTING_CHANNEL
+    printf ("Does not exist (%s): %g\n",
+        channel_state_str[ca_state(doesnotexistID)],
+        doesnotexist);
+#endif
+    printf ("Gap          (%s): %g\n",
+        channel_state_str[ca_state(gapID)],
+        gap);
+    
+    /* Last step: free all channel access resources */
+    ca_task_exit();
+    return 0;  
+}