I fixed the compilation of musbstd.h (it required -DHAVE_LIBUSB on Linux, but
nothing knew about defining it) and put musbstd.o back into libmidas (USB
support should be part of the standard base midas library). K.O.

> I fixed the compilation of musbstd.h (it required -DHAVE_LIBUSB on Linux, but
> nothing knew about defining it) and put musbstd.o back into libmidas (USB
> support should be part of the standard base midas library). K.O.

I'm not so sure about that. One could consider musbstd.o as a driver, and the
philosophy used for midas programs is that drivers get added explicitly when
compiling a frontend. We do not put mvmestd.c and mcstd.c into libmidas since for
different interfaces a different driver might be required. If we at some point use
an usb library different than libusb.a, we would have to compile different
libmidas for these different drivers.

I know it's convenient to have things in libmidas and not having to specify it
expliceitely for each frontend, but it is then somehow inconsistent with drivers
for vme and camac. So please reconsider this again.

- Stefan

Fresh svn checkout of MIDAS does not build on Fedora 5, I get this error:

cc -c -g -O2 -Wall -Wuninitialized -Iinclude -Idrivers -I../mxml -Llinux/lib
-DINCLUDE_FTPLIB   -D_LARGEFILE64_SOURCE -DHAVE_ROOT -pthread
-I/triumfcs/trshare/olchansk/root/root_v5.10.00_SL40/include -m32 -DOS_LINUX
-fPIC -Wno-unused-function -o linux/lib/odb.o src/odb.c
src/odb.c: In function 'db_open_database':
src/odb.c:805: warning: dereferencing type-punned pointer will break
strict-aliasing rules
src/odb.c: In function 'db_lock_database':
src/odb.c:1350: warning: dereferencing type-punned pointer will break
strict-aliasing rules
cc: Internal error: Segmentation fault (program cc1)
Please submit a full bug report.
See <URL:http://bugzilla.redhat.com/bugzilla> for instructions.
make: *** [linux/lib/odb.o] Error 1

If I compile odb.c without "-O2", the rest of MIDAS builds without any more errors.

The observed warnings are (I do not know what they mean):
warning: dereferencing type-punned pointer will break strict-aliasing rules
warning: missing sentinel in function call (Cannot do without sentinels, eh?)
warning: pointer targets in passing argument 3 of 'getsockname' differ in signedness
warning: non-local variable '<anonymous struct> out_info' uses anonymous type

The "invalid lvalue" errors seem to have been successfully vanquished.

K.O.

I commited the latest VMIC VME driver we use at TRIUMF. It has working support
for D32 and D64 DMA and can move data from the SIS3820 multiscaler through the
MIDAS frontend at > 30 Mbytes/sec on our VMICVME-7805 machines. The actual DMA
speed on the VME bus is around 50 Mbytes/sec, effective data rate is lower
because of a memcpy() from the kernel DMA buffer into user memory (required by
the MIDAS mvmestd.h interface, quite inefficient for DMA operations). K.O.

When using mhist interactively, I could not look at array data:
1) if the array is the only variable, the question "what array index to use?"
was not asked, zero was assumed,
2) even if the question was asked, the answer was ignored, zero was used.
Fixes commited to utils/mhist.c
K.O.

It appears that the latest version of MIDAS malfunctions on PowerPC/VxWorks
machines, below are two problem reports. As reported, previous versions of MIDAS
work fine, I guess that reduces the probability of it being buggy user code. At
least one of the problems feels like a missing endian conversion somewhere, but
I am not aware of any recent changes in the MIDAS RPC code... We will be trying
to debug both problems, but any insight would be greatly appreciated.

K.O.


From suz@triumf.ca  Tue May 30 16:58:16 2006
Date: Tue, 30 May 2006 16:58:16 -0700 (PDT)
From: Suzannah Daviel <suz@triumf.ca>
To: konstantin olchanski <olchansk@triumf.ca>
Subject: rpc problems

Hi Konstantin,

Herewith a description of the problems,

Suzannah

Problem on system A:
--------------------

After upgrading the Linux operating system from RH9 to SL4, and installing
latest Midas software, the first time a manual trigger is issued, the VxWorks
frontend (running
on a PPC) crashes:


Output on PPC consol:

trigger histo event from status page

rpc_client_accept: starting with sock:11

program
Exception current instruction address: 0x01ac7388
Machine Status Register: 0x0008b030
Condition Register: 0x24000082
Task: 0x1b47908 "mfe"



The histo event is usually large so is fragmented. It is sent out by a
manual trigger and at end of run. When the run is ended (before an event
request using a manual trigger so program has not yet crashed) the histo
event is sent successfully.

After returning to the previous version of Midas but still running SL4,
this problem disappeared.




Problem on system B:
--------------------

Again, SL9 was installed, and the Midas software updated to the latest.
When sending a periodic (non-fragmented) event, after a while, one of the
parameters appears to become corrupted, and a lot of rpc_call error
messages appear. These continue while data is still successfully sent out
until the run is ended.



Tue May  9 05:20:29 2006 [Mdarc] *** data saved in file
/is01_data/bnmr/dlog/2006/040377.msr_v5 at Tue May  9 05:20:29
2006 (SN=5) ***
Tue May  9 05:21:30 2006 [Mdarc] *** data saved in file
/is01_data/bnmr/dlog/2006/040377.msr_v6 at Tue May  9 05:21:30
2006 (SN=6) ***
Tue May  9 05:22:31 2006 [Mdarc] *** data saved in file
/is01_data/bnmr/dlog/2006/040377.msr_v7 at Tue May  9 05:22:31
2006 (SN=7) ***

Tue May  9 05:23:12 2006 [feBNMR] [midas.c:9325:rpc_call] parameters
(1099059848) too large for network buffer
(524344); param_size=1099059808
Tue May  9 05:23:12 2006 [feBNMR] [midas.c:9325:rpc_call] parameters
(1099059848) too large for network buffer
(524344); param_size=1099059808
........................................
Tue May  9 05:23:31 2006 [feBNMR] [midas.c:9325:rpc_call] parameters
(1099059848) too large for network buffer
(524344); param_size=1099059808
Tue May  9 05:23:32 2006 [feBNMR] [midas.c:9325:rpc_call] parameters
(1099059848) too large for network buffer
(524344); param_size=1099059808

Tue May  9 05:23:32 2006 [Mdarc] *** data saved in file
/is01_data/bnmr/dlog/2006/040377.msr_v8 at Tue May  9 05:23:32
2006 (SN=8) ***

Tue May  9 05:23:32 2006 [feBNMR] [midas.c:9325:rpc_call] parameters
(1099059848) too large for network buffer
(524344); param_size=1099059808
Tue May  9 05:23:33 2006 [feBNMR] [midas.c:9325:rpc_call] parameters
(1099059848) too large for network buffer
(524344); param_size=1099059808
etc.

Another example showing that the corrupted parameter varies in size:

Thu Apr 13 19:00:00 2006 [mhttpd] Run #30005 started
Thu Apr 13 19:00:08 2006 [Mdarc] *** Saved data file
/is01_data/bnmr/dlog/2006/030005.msr_v1 at Thu Apr 13 19:00:08 2006 ***
Thu Apr 13 19:01:10 2006 [Mdarc] *** Saved data file
/is01_data/bnmr/dlog/2006/030005.msr_v2 at Thu Apr 13 19:01:10 2006 ***
Thu Apr 13 19:02:14 2006 [Mdarc] *** Saved data file
/is01_data/bnmr/dlog/2006/030005.msr_v3 at Thu Apr 13 19:02:14 2006 ***
Thu Apr 13 19:03:20 2006 [Mdarc] *** Saved data file
/is01_data/bnmr/dlog/2006/030005.msr_v4 at Thu Apr 13 19:03:20 2006 ***
Thu Apr 13 19:04:22 2006 [Mdarc] *** Saved data file
/is01_data/bnmr/dlog/2006/030005.msr_v5 at Thu Apr 13 19:04:22 2006 ***
Thu Apr 13 19:05:12 2006 [feBNMR] [midas.c:9323:rpc_call] parameters
(1077739560) too large for network buffer
(524344)
Thu Apr 13 19:05:13 2006 [feBNMR] [midas.c:9323:rpc_call] parameters
(1077739560) too large for network buffer
(524344)
etc.

There is a crash in odbedit when loading some xml odb files: a missing check for NULL pointer when 
loading an array of strings and one of the array elements is blank. This check is present when loading 
other string values. Here is the diff:

-bash-3.00$ diff odb.c odb.c-new
5621c5621,5624
<                db_set_data_index(hDB, hKey, mxml_get_value(child), size, i, tid);
---
>                if (mxml_get_value(child) == NULL)
>                   db_set_data_index(hDB, hKey, "", size, i, tid);
>                else
>                   db_set_data_index(hDB, hKey, mxml_get_value(child), size, i, tid);

K.O.

Our VxWorks C compiler (gcc-2.8-something) does not like the "//" comments. Luckily, on VxWorks, we 
only compile a small subset of midas, so there is no point in banning all "//" comments. But I did have to 
convert a couple of them to /* commens */ in odb.c to make it compile. Changes to odb.c commited. K.O.

Fellow Midasites- we are receiving reports that current Midas sources do not compile on Fedora 4 (and 5?) 
with errors "invalid lvalue in assignment". It looks like the new compilers reject what looks to my eye like 
perfectly valid C code that we have been writing since the beginning of C. Any suggestions on the best fix? 
K.O.

I am debugging a Rome-based DAQ system setup by Pierre A. (the system does not
work because of bugs in Rome).

One problem I see is with my copy of cm_register_transition() in midas.c. Rome
calls it with a NULL function to register a "queued" transition, but the
cm_register_transition() code has changed around (rev 3051) to make NULL mean
"unregister" a transition (this broke the queued transitions used by Rome), then
it got changed back (rev 3085). Of course, I was stuck with the broken version,
so Rome did not work at all, and it cost me real wall time to get to the bottom
of all this, only to discover that this problem is already fixed. So-

I would greatly appreciate it if, in the future, changes (and bug fixes) to the
MIDAS API were announced on this mailing list here.

K.O.

> I am debugging a Rome-based DAQ system setup by Pierre A. (the system does not
> work because of bugs in Rome).
> 
> One problem I see is with my copy of cm_register_transition() in midas.c. Rome
> calls it with a NULL function to register a "queued" transition, but the
> cm_register_transition() code has changed around (rev 3051) to make NULL mean
> "unregister" a transition (this broke the queued transitions used by Rome), then
> it got changed back (rev 3085). Of course, I was stuck with the broken version,
> so Rome did not work at all, and it cost me real wall time to get to the bottom
> of all this, only to discover that this problem is already fixed. So-
> 
> I would greatly appreciate it if, in the future, changes (and bug fixes) to the
> MIDAS API were announced on this mailing list here.
> 
> K.O.

Yes you are right. I apologize. Fact was that I was not aware that anybody else uses
already ROME in online mode. Nevertheless, let me at least explain the reason for
that change:

Some experiments at PSI run a slow control front end, which talks to pretty slow
hardware, and thus can be nonresponsive for many seconds. Since each frontend by
default registers in the start and stop transitions, this frontend delayed the start
/stop of each run. To solve this problem in the short run, the frontend should not
register in the transition. Originally I implemented this by using the NULL function
pointer, until we figured out that ROME uses this to register (not de-register)
together with the cm_query_transition() function. Therefore a new function
cm_deregister_transition() was implemented and is used now by the slow frontends.

In the long run this will be solved by implementing multi-threaded frontends which
get one thread for each equipment and therefore do not block any transition anymore.

I commited fixes for a few minor compilation errors in the VME drivers
(vmicvme.c, etc)
I also added new drivers for the v513 latch and v560 scaler that I wrote for
CERN-ALPHA.

(Maybe I should mention that we also have drivers for the SIS 3820 multiscaler,
the v895 VME discriminator and a few more modules. Will commit them as they mature).

K.O.

 Hi,
I was trying to update the checkout of Midas, but it looks like something is not
working - maybe a component of the Savannah system:
[sergio@daq-pc midas-SVN]$ svn update
svn@savannah.psi.ch's password: svn
unix dgram connect: Connection refused at /bin/cvssh.pl line 32
no connection to syslog available at /bin/cvssh.pl line 32
svn: Connection closed unexpectedly

my .svn/entries says (amongst the rest)
 url="svn+ssh://svn@savannah.psi.ch/afs/psi.ch/project/meg/svn/midas/trunk"
and yes, it used to work well... 

Cheers,
  Sergio

>  Hi,
> I was trying to update the checkout of Midas, but it looks like something is not
> working - maybe a component of the Savannah system:
> [sergio@daq-pc midas-SVN]$ svn update
> svn@savannah.psi.ch's password: svn
> unix dgram connect: Connection refused at /bin/cvssh.pl line 32
> no connection to syslog available at /bin/cvssh.pl line 32
> svn: Connection closed unexpectedly
> 
> my .svn/entries says (amongst the rest)
>  url="svn+ssh://svn@savannah.psi.ch/afs/psi.ch/project/meg/svn/midas/trunk"
> and yes, it used to work well... 
> 
> Cheers,
>   Sergio

I just tried now and it seemed to work fine. Do you still have the problem?

- Stefan

> I just tried now and it seemed to work fine. Do you still have the problem?
> 
> - Stefan

 The problem was still there this morning, shortly after seeing your mail, but seems
to be fixed now.
 BTW, which is the best way to submit patches ? I have a version of khyt1331 for Linux
kernel 2.6 (we are running Scientific Linux 4.1), and a few smaller things, mostly in
the examples. 

 Thanks, Sergio

It turns out the the standard event builder fragment matching algorithm cannot
be used in my TPC application. I have two TPC-USB interfaces, which lack any
"busy" or synchronization logic. I send the hardware trigger into both
interfaces, and if one of them misses it, the data is out of sync forever. Consider:

Hardware
trigger    trig1     trig2    trig3    trig4
TPC01      serial1   serial2  serial3  serial4
TPC02      serial1  (missing) serial2  serial3

With the event builder matching only the event serial numbers, the first event
will be okey, but the second event will have trig2 data from TPC01 and trig3
data from TPC02, etc.

The problem exists even if the TPC-USB interfaces do not miss any triggers:
during begin and end of run, the interfaces are enabled one at a time, so if a
trigger arrives after the first interface was enabled, but before the second is
enabled, the data starts being out of sync (and if the same happens during the
end-of-run, the event counts from both frontends will match, but all data would
*still* be out of sync).

Obviously additional data is needed to match the fragments.

So in each frontend, I have a high-precision timestamp (gettimeofday(), usec
resolution) and I would like to have the event builder match the timestamps
instead of event serial numbers. What is the best way to do this? The mevb.c
code does not have any user callbacks for checking "do these fragments belong to
the same event?".

P.S. The event rate will be about 1/sec from cosmic ray tests and at most
10-50/sec in the M11 beam line at TRIUMF, at these low rates, the gettimeofday()
timestamps should be adequate.

K.O.

> It turns out the the standard event builder fragment matching algorithm cannot
> be used in my TPC application. I have two TPC-USB interfaces, which lack any
> "busy" or synchronization logic. I send the hardware trigger into both
> interfaces, and if one of them misses it, the data is out of sync forever. Consider:
> 
> Hardware
> trigger    trig1     trig2    trig3    trig4
> TPC01      serial1   serial2  serial3  serial4
> TPC02      serial1  (missing) serial2  serial3
> 
> With the event builder matching only the event serial numbers, the first event
> will be okey, but the second event will have trig2 data from TPC01 and trig3
> data from TPC02, etc.

Well, I would say: this is a very poor design of an experiment. Before curing the
problems in software, I first would consider a redesign of the data readout scheme with
a global hardware trigger and a hardware busy.

> So in each frontend, I have a high-precision timestamp (gettimeofday(), usec
> resolution) and I would like to have the event builder match the timestamps
> instead of event serial numbers.

What do you do if the frontend clock drifts away? I have seen drifts of up to 10 sec/day
on some PCs, so your required accuracy of 1/50 s would be violated after 3 minutes. You
would have to synchronize your clocks constantly. If your synchronization algorithm
determines a clock is out of sync and adjusts it, and the delta t is more than 1/50 sec,
you are screwed.

So all together I conclude that this proposed synchronization scheme is pretty dangerous
and could ruin the whole experiment.

> What is the best way to do this? The mevb.c
> code does not have any user callbacks for checking "do these fragments belong to
> the same event?".

Pierre can answer that.

- Stefan

At DANCE we have a similar issue.  We are still doing "software
handshaking" between multiple frontends (15 which read data, and 16th
with direct accessto the trigger logic), and we apply a time stamp
using gettimeofday().  We use the regular mevb, sorting on serial number.

In the analyzer (MIDAS or ROME) we then keep a big circular buffer of
event fragments, which are rebuilt into new events based on the time stamp
obtained from gettimeofday().  We keep the system clocks synchronized
(often to within about 1ms) using ntp (need to average over several
ntp servers to avoid issues with network noise).  ntp can take a while
to stabilize, so we never reboot our computers... (well almost never).
We have a slow control frontend which monitors the ntp time offsets and
put's them in the history system for easy visualization.

Occasionally we seem to get in a mess, but somehow this fixes itself on
the next run, so it has been a useable system.  Maybe one day we will
get hardware handshaking between the frontend computers and the trigger
logic, but in the meantime we are taking data.

John.

When I wrote the musbstd.h "open" method, I kind of punted on the problem of
handling multiple identical USB devices. Instead of a real solution, I added an
"instance" parameter, which allows one to "open" the "first", "second", etc USB
device, as listed in a magic random system dependant order.

Normally, USB devices are identified by two 16-bit integers: manufacturer ID and
product ID (i.e. as reported by "lsusb"). This works well until one has more
than one "identical" device. Two years ago, I had 5 identical USB cameras
(optical alignement system for TRIUMF-TWIST); last year, I had multiple USB
serial adapters; today I have two identical USB-TPC interfaces.

Most of the time, the devices are plugged into the same USB ports, so
theoretically, one should be able to tell exactly which one is which ("upstream
camera is plugged into port 1, downstream camera is plugged into port 2"). But
in the magic system dependant enumeration order, they keep moving around,
depending on the order of enumeration, history of powering up and down, phase of
the Moon, etc.

So my generic "musbstd" method of "open first", "open second", etc turned out to
be completely disfunctional.

So far, I am unable to come up with a system independant solution. But I have a
solution for Linux and maybe for MacOSX:

1) on Linux, I can use the information parsed from /proc/bus/usb/devices to say
"please open the USB device on USB bus 1, port 1", the so called USB device
"path", as seen in the system log and in /sys/bus/usb/devices.

2) on MacOSX, I was unable to find a way to discover the USB topology, but they
seem to maintain an uint32_t "location", which they promise to keep at least
across reboots (did not check this yet).

3) Windows I did not look at yet.

So we have a choice:

a) use system dependant "musb_open_linux(usbpath,vendor,product)",
"musb_open_macosx(???,vendor,product)", etc

b) create order out of chaos by manually keeping a map of "instances" (first,
second, third device) to "persistant addresses". On Linux, it would be a file
containing something like this: "USB-TPC-0 is on bus1-port1, USB-TPC-1 is on
bus1-port2". Then again, I can say "please open USB-TPC interface instance 0" or
"instance 1", etc. There is a small difficulty with dealing with devices
temporarily or permanantly going away, or changing physical addresses ("I moved
the USB device from port 1 to port 3"). This could be handled by telling the
user "hmm... USB topology has changed, please delete the map file and try
again", or we could come up with something more user friendly.

Any thoughts?

P.S. For my immediate need (I need this tomorrow), I will write a
musb_open_linux(usbpath,vendor,product) function.

K.O.

> Any thoughts?

I got an idea of how to solve this problem in an OS-independent manner. The USB
devices and hubs form a tree, like this

  Root  HUB
  0   1   2
  |   |   \__...
  |   \___
 DevY     \
         HUB
        0 1 2
        |   |
        |  DevX
       HUB
      0 1 2
          |
        DevZ

This tree can be considered as an ordered tree, if you read it from left to right.
In that order, the devices are orderd

DevY - DevZ - DevX

Since the devices are ordered, the "instance" parameter from musb_init can be used
to identify them uniquely, like

instance==0   => DevY
instance==1   => DevZ
instance==2   => DevX

So I would say that we can use the current API using the "instance" parameter to
uniquely access a device. All we have to do is to build that tree, sort it, and then
use the instance parameter as an entry to that tree. The sorting takes care of
different ordering, which can happen during enumeration (depeding on power-up
sequence, phase of the Moon etc.). So if you have three devices like above, DevZ
should alway be at "instance==1". The only problem is if you unplug DevY for
example, then you get the map

instance==0   => DevZ
instance==1   => DevX

which is different from above. But if you have a different number of devices, you
likely have to change your frontend cody anyhow, so you can change the device
mapping there as well. 

In order to simplify the code, I would not build a complete tree and sort it, but
scan the whole tree hierarchically, i.e. look at

Bus1/Port1
Bus1/Port2
Bus1/...
Bus2/Port1
Bus2/Port2
...

Since there is a maximum of toal 127 USB devices, this scan should be pretty quick.
If you find a device with matching vendor and product ID, you increment an internal
counter. If that counter matches your instance parameter, you open that device.

The ultimate solution of course is to put an additional address into each device, so
you can distinguish them easily. For a out-of-the box Web cam you probably have no
chance, but for the home-made MSCB nodes I put such an address into each node, so I
can distinguish them even if the have the same product and vendor ID.

If a variable under "/experiment/edit on start/" is an array, it is correctly
offered for editing on the "start run page", but then all elements in the array
end up set to the value of the first element.

This appears to be an error in mhttpd.c:interprete(), in the "start dialog"
section. The non-working version in CVS reads:

               for (j = 0; j < key.num_values; j++) {
                  size = key.item_size;
                  sprintf(str, "x%d", n++);
                  db_sscanf(getparam(str), data, &size, j, key.type);
                  db_set_data_index(hDB, hsubkey, data, size + 1, j, key.type);
               }

the fix that works for me reads:
                  db_sscanf(getparam(str), data, &size, 0, key.type);

(notice: the argument "j" is replaced with "0").

The way I understand this, all array elements are encoded into individual HTTP
thingy strings, named sequentially x0, x1, ... and when we parse the values out
of them, the array index should never show up.

(Stefan, if you can, please commit a fix to svn).

K.O.

> If a variable under "/experiment/edit on start/" is an array, it is correctly
> offered for editing on the "start run page", but then all elements in the array
> end up set to the value of the first element.

You are right. This was was there from the beginning, you are just the first one
trying "edit on start" with an array. I applied your fix and committed to SVN
reviwion 3013.

Stefan

Minor changes to run transitions code:
- improve debug messages
- fail transition if cannot connect to one of the clients
K.O.

> Minor changes to run transitions code:
> - fail transition if cannot connect to one of the clients

This change introduced a problem:
1) a run is happily taking data
2) a frontend crashes
3) the web interface cannot stop the run (cannot contact the crashed frontend)
until  it is removed by the timeout (10-60 seconds?).

I am now considering allowing the run to end even if some clients cannot be
contacted. The begin, pause and resume transitions would continue to fail if
clients cannot be contacted.

K.O.

> I am now considering allowing the run to end even if some clients cannot be
> contacted. The begin, pause and resume transitions would continue to fail if
> clients cannot be contacted.

Sounds like a good idea.

- Stefan

My TPC events are fairly large: 18 FEC cards * 128 channels per card * 2 Kbytes
per channel = about 4 Mbytes. In my
frontend, when I request this event size, MIDAS complaints (in mfe.c) that it is
bigger than MAX_EVENT_SIZE, which
is set to 0.5 Mbytes in midas.h. What is the best way to deal with this? Should
we increase MAX_EVENT_SIZE to
something bigger? Remove the MAX_EVENT_SIZE limitation altogether?
  
For now, I increased the value MAX_EVENT_SIZE & co to (10*1024*1024) and it
seems to work (I also had to bump the
sanity check in bm_open_buffer() from 10E6 to 100E6). With 1/4 of the FEC cards,
the event size is 1 Mbyte at ~6
ev/sec the machine is almost idle, with the biggest CPU user being the event
builder at 10% CPU utilization.

K.O.

> My TPC events are fairly large: 18 FEC cards * 128 channels per card * 2 Kbytes
> per channel = about 4 Mbytes. In my
> frontend, when I request this event size, MIDAS complaints (in mfe.c) that it is
> bigger than MAX_EVENT_SIZE, which
> is set to 0.5 Mbytes in midas.h. What is the best way to deal with this? Should
> we increase MAX_EVENT_SIZE to
> something bigger? Remove the MAX_EVENT_SIZE limitation altogether?

If you teach me how to remove the MAX_EVENT_SIZE, that would be perfect!

Unfortunately the limit comes from the shared memory on the back end (the so-called
"SYSTEM" shared memory). Due to the structure of the buffer manager, the shared
memory has to hold at least two events simultaneously. And once the shared memeory
is created, it's size cannot be changed without restarting all the clients. That's
the origin of the MAX_EVENT_SIZE. In former days, the total allowed shared memory on
a typical linux machine was 2MB. That's why I set MAX_EVENT_SIZE to 0.5 MB, so midas
takes 2*0.5MB=1MB plus 0.2MB for the ODB, leaving 0.8MB for other applications.
Nowadays, the shared memory might be bigger (actually it's a parameter during kernel
compilation), so one could consider increasing the default MAX_EVENT_SIZE. If you
make a survey of the shared memory sizes in some of the current distributions, we
can choose a safe value.

> For now, I increased the value MAX_EVENT_SIZE & co to (10*1024*1024) and it
> seems to work (I also had to bump the
> sanity check in bm_open_buffer() from 10E6 to 100E6). With 1/4 of the FEC cards,
> the event size is 1 Mbyte at ~6
> ev/sec the machine is almost idle, with the biggest CPU user being the event
> builder at 10% CPU utilization.

I made sure that there is no other limitation as the one given by MAX_EVENT_SIZE, so
it should work fine. Thanks for telling me the wrong sanity check, that should be
changed in the repository.

I would like to document a few problems I ran into while setting up a new
experiment (two USB interfaces to Alice TPC electronics, plus maybe a USB
interface to CAMAC). I am using a midas cvs checkout from last October, so I am
not sure if these problems exist in the very latest code. I have fixes for all
of them and I will commit them after some more testing and after I figure out
how to commit into this new svn thingy.

- mxml: writing xml into an in-memory buffer probably produces invalid xml
because one of the mxml functions always writes "/>" into writer->fh, which is 0
for in-memory writers, so the "/>" tag goes to the console instead of the xml
data stream.

- hs_write_event() closes fd 0 (standard input), which confuses ss_getch(),
which makes mlogger not work (at least on my machine). I traced this down to the
history file file descriptors being initialized to zero and hs_write_event()
closing files without checking that it ever opened them.

- mevb: event builder did not work with a single frontend (a two-liner fix, once
Pierre showed me where to look. Why? My second TPC-USB interface did not yet
arrive and I wanted to test my frontend code. Yes, it had enough bugs to prevent
the event builder from working).

- mevb: consumes 100% CPU. Fix: add a delay in the main busy-loop.

- mlogger ROOT tree output does not work for data banks coming through the event
builder: mlogger looks for the bank definition under the event_id of mevb, in 
/equipment/evb/variables, which is empty, as the data banks are under
/equipment/frontendNN/variables. This may be hard to fix: bank "TPCA" may be
under "fe01", "TPCB" under "fe02" and mlogger knows nothing about any of this.
Fix: go back to .mid files.

K.O.