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    Reply  26 Feb 2021, Isaac Labrie Boulay, Forum, Javascript error during run transitions. 
> > 
> > I have also attached a screen capture of the output.
> > 
> 
> so the error is gone?
> 
> K.O.

Hi K.O.,

No the error persists, 
Entry  14 Oct 2016, Konstantin Olchanski, Info, Javascript based run start and stop pages. 
I switched mhttpd to use the new javascript based run start and stop pages.

There are two new html pages:

resources/start.html - mimics the old run start page exactly - where you can enter the "edit on 
start" parameters and start the run.
resources/transition.html - monitors the transition progress, shows the status of every transition 
client, their sequence number, waiting list dependency, time spent making rpc calls, etc.

If the new pages do not work for you, please report it here and switch to the old pages
by editing src/mhttpd.cxx - comment-out the line "#define NEW_START_STOP 1"

K.O.
    Reply  05 Dec 2016, Thomas Lindner, Info, Javascript based run start and stop pages. 
> I switched mhttpd to use the new javascript based run start and stop pages.

One initial complaint: the transition.html page doesn't seem to deal well with a frontend program using
a deferred transition.  Specifically, I find with my simulated frontend ([1]), which has a deferred
end-of-run transition, that two problems happen:

i) the page doesn't give any indication that a frontend has a deferred transition; in fact it says that
the frontend immediately has finished the transition.
ii) once the deferred transition has finished, the page doesn't switch to saying that the run has
stopped.  In fact, even if I reload the transition page it still continues to show that the run is
ongoing; the status page, by contrast, shows that the run has stopped.

I separately still think that the transition page should automatically go away after 5 seconds
(assuming that all the transitions were successful).  I think it is annoying that you need to click
back to the status page.

[1] https://github.com/thomaslindner/fesimdaq
    Reply  01 Feb 2017, Konstantin Olchanski, Info, Javascript based run start and stop pages. 
> > I switched mhttpd to use the new javascript based run start and stop pages.
> 
> One initial complaint: the transition.html page doesn't seem to deal well with a frontend program using
> a deferred transition.
>

We now have a test frontend for deferred transitions, and this problem will likely be fixed.

> 
> I separately still think that the transition page should automatically go away after 5 seconds
>

This is a user-interface philosophy issue.

Instead of using personal preferences one should follow established design principles
(there is research done and books written about this).

I did not recently look at current recommendations for this type of interaction, but generally
one expects web pages to "do things" (such as switch to a different page) only when directed
by user input (press a button).

My personal opinion is that half the users will find 5 sec delay too slow, the other half will
find 5 sec too fast and the 3rd half will wonder "what happened, the web page flashed and disappeared,
did I miss something important, how do I get back to whatever is was?!?".

One idea is to implement the transition page as a implant on the state page - after the "start" page
you go back to the status page where you can see the progress of the transition. After the transition
completes, it's progress window "collapses" into a "success/failure" display with a link to the full
transition page to see any details of what happened. Any volunteers? (I would html-ize the status page first).

K.O.
    Reply  01 Feb 2017, Stefan Ritt, Info, Javascript based run start and stop pages. 
> > > I switched mhttpd to use the new javascript based run start and stop pages.
> > 
> > One initial complaint: the transition.html page doesn't seem to deal well with a frontend program using
> > a deferred transition.
> >
> 
> We now have a test frontend for deferred transitions, and this problem will likely be fixed.
> 
> > 
> > I separately still think that the transition page should automatically go away after 5 seconds
> >
> 
> This is a user-interface philosophy issue.
> 
> Instead of using personal preferences one should follow established design principles
> (there is research done and books written about this).
> 
> I did not recently look at current recommendations for this type of interaction, but generally
> one expects web pages to "do things" (such as switch to a different page) only when directed
> by user input (press a button).
> 
> My personal opinion is that half the users will find 5 sec delay too slow, the other half will
> find 5 sec too fast and the 3rd half will wonder "what happened, the web page flashed and disappeared,
> did I miss something important, how do I get back to whatever is was?!?".
> 
> One idea is to implement the transition page as a implant on the state page - after the "start" page
> you go back to the status page where you can see the progress of the transition. After the transition
> completes, it's progress window "collapses" into a "success/failure" display with a link to the full
> transition page to see any details of what happened. Any volunteers? (I would html-ize the status page first).
> 
> K.O.

I agree with Konstantin's plans and volunteer for the "collapsable" display. We will address this during my next visit to TRIUMF.
Entry  21 Feb 2014, Konstantin Olchanski, Info, Javascript ODBMLs(), modified ODBMCopy() JSON encoding 
I made a few minor modifications to the ODB JSON encoder and implemented a javascript "ls" function to 
report full ODB directory information as available from odbedit "ls -l" and the mhttpd odb editor page.

Using the new ODBMLs(), the existing ODBMCreate(), ODBMDelete() & etc a complete ODB editor can be 
written in Javascript (or in any other AJAX-capable language).

While implementing this function, I found some problems in the ODB JSON encoder when handling 
symlinks, also some problems with handling symlinks in odbedit and in the mhttpd ODB editor - these are 
now fixed.

Changes to the ODB JSON encoder:
- added the missing information to the ODB KEY (access_mode, notify_count)
- added symlink target information ("link")
- changed encoding of simple variable (i.e. jcopy of /experiment/name) - when possible (i.e. ODB KEY 
information is omitted), they are encoded as bare values (before, they were always encoded as structures 
with variable names, etc). This change makes it possible to implement ODBGet() and ODBMGet() using the 
AJAX jcopy method with JSON data encoding. Bare value encoding in ODBMCopy()/AJAX jcopy is enabled by 
using the "json-nokeys-nolastwritten" encoding option.

All these changes are supposed to be backward compatible (encoding used by ODBMCopy() for simple 
values and "-nokeys-nolastwritten" was previously not documented).

Documentation was updated:
https://midas.triumf.ca/MidasWiki/index.php/Mhttpd.js

K.O.
Entry  20 Jun 2011, Stefan Ritt, Info, Javascript ODB interface revised 
The Javascript interface to the ODB has been revised. This extends the capabilities of custom web pages requesting data from the ODB. By grouping several request together, the number of round-trips is minimized and the response time is reduced. Following functions are new or extended:

  • ODBGet(path[, format]): This functions works now also with subdirectories in the ODB. The command ODBGet('/Runinfo') returns for example:
    1
    1
    1024
    0
    0
    0
    Mon Jun 20 09:40:14 2011
    1308588014
    Mon Jun 20 09:40:46 2011
    1308588046
    

  • ODBGetRecord(path), ODBExtractRecord(key): While ODBGet can be used for subdirectories, an easier way is to use ODBGetRecord and ODBExtractRecord. The first function retrieves the subtree (record), while the second one can be used to extract individual items. Here is an example:
    result = ODBGetRecord('/Runinfo');
    run_number = ODBExtractRecord(result, 'Run number');
    start_time = ODBExtractRecord(result, 'Start time');
    

  • ODBMGet(paths[, callback, formats]): This function ("Multi-Get") can be used to obtain ODB values from different paths in one call. The ODB paths have to be supplied in an array, the result is again an array. An optional callback routine might be supplied for asynchronous operation. Optional formats might be supplied if the resulting number should be formatted in a specific way. Here is an example:
       var req = new Array();
       req[0] = "/Runinfo/Run number";
       req[1] = "/Equipment/Trigger/Statistics/Events sent";
       var result = ODBMGet(req);
       run_number = result[0];
       events_sent = result[1];
    

The new functions are implemented in mhttpd revision 5075.
Entry  10 Oct 2022, Zaher Salman, Suggestion, JSON-RPC function to read files mjsonrpc_user.cxx
Hello ,

The midas sequencer uses the function js_seq_list_files to get a list of files in the /Sequencer/State/Path with extension *.msl. It would be nice to generalize this function to be able to read files with other (or any) extension.

Based on the js_seq_list_files I added a function in js_any_list_files mjsonrpc_user.cxx (attached) which does the job. Maybe a better/safer implementation can be made in midas. Are there any plans to do this?

thanks.
    Reply  19 Oct 2009, Exaos Lee, Forum, It' better to fix this warnings 
> There is no "type conversions". The compiler is whining about code like this:
>
> /* data type names */
> static char *tid_name[] = {
> "NULL",
> "BYTE",
> ...
>
> I guess we should keep the compiler happy and make them "static const char*".
>
> BTW, my compiler is SL5.2 gcc-4.1.2 and it does not complain. What's your compiler?
>
> K.O.

When I use "make" with odbedit, the generated "experim.h" also contains such codes as:
#define EXPCVADC_COMMON_STR(_name) char *_name[] = {\
"[.]",\
...
This will cause "type conversion" warnings. I hope that "odbedit" can generate codes like this:
#define EXPCVADC_COMMON_STR(_name) const char *_name[] = {\
"[.]",\
...
In fact, "const char*" is enough to suppress the warnings. Using "const char* foo=\"blarblar\"" is a good habit because it can avoid the following bugs:
char *s = "whatever";
...
strcpy(s, "Hello, this is a string longer than the initial one.");
The above code can successfully generate an executable, but it will encounter segmentation fault while executing. "const char*" means we should not change the variable in other place, which is important to suppress bugs.

Another problem, if I change the "experim.h" as I wished, new warnings appeared when the compiler parsing the following code:
status = db_create_record(hDB, 0, set_str, strcomb(expcvadc_settings_str));
Warning:
cvadcfe.c: In function ‘frontend_init’:
cvadcfe.c:144: warning: passing argument 1 of ‘strcomb’ from incompatible pointer type
    Reply  10 Nov 2009, Stefan Ritt, Forum, It' better to fix this warnings 
> This will cause "type conversion" warnings. I hope that "odbedit" can generate codes like this:
>
> #define EXPCVADC_COMMON_STR(_name) const char *_name[] = {\
> "[.]",\
>...

Ok, I changed that in odb.c rev. 4620, should be fine now.
Entry  02 Aug 2023, Caleb Marshall, Forum, Issues with Universe II Driver  

Hello,

At our lab we are currently in the process of migrating more of our systems over to Midas. However, all of our working systems are dependent on SBCs with the Tsi-148 chips of which we only have a handful. In order to have some backups and spares for testing, we have been attempting to get Midas working with some borrowed SBCs (Concurrent Technologies VX 40x/04x) with Universe-II chips. The SBC is running CentOS 7. I have tried to follow the instructions posted here. The universe-II kernel module appears to load correctly, dmesg gives:

[   32.384826] VME: Board is system controller
[   32.384875] VME: Driver compiled for SMP system
[   32.384877] VME: Installed VME Universe module version: 3.6.KO6
 

However, running vmescan.exe fails with a segfault. Running with gdb shows:

vmic_mmap: Mapped VME AM 0x0d addr 0x00000000 size 0x00ffffff at address 0x80a01000
mvme_open:
Bus handle              = 0x7
DMA handle              = 0x6045d0
DMA area size           = 1048576 bytes
DMA    physical address = 0x7ffff7eea000
vmic_mmap: Mapped VME AM 0x2d addr 0x00000000 size 0x0000ffff at address 0x86ff0000

Program received signal SIGSEGV, Segmentation fault.
mvme_read_value (mvme=0x604010, vme_addr=<optimized out>)
    at /home/jam/midas/packages/midas/drivers/vme/vmic/vmicvme.c:352
352        dst  = *((WORD *)addr);
 

With the pointer addr originating from a call to vmic_mapcheck within the  mvme_read_value functions in the vmicvme.c file. Help with where to go from here would be appreciated.

-Caleb 

 

    Reply  02 Aug 2023, Konstantin Olchanski, Forum, Issues with Universe II Driver  
I maintain the tsi148 and the universe-II drivers. I confirm -KO6 is my latest 
version, last updated for 32-bit Debian-11, and we still use it at TRIUMF.

It is good news that the vme_universe kernel module built, loaded and reported 
correct stuff to dmesg.

It is not clear why mvme_read_value() crashed. We need to know the value of 
vme_addr and addr, can you add printf()s for them using format "%08x" and try 
again?

K.O.

<p>&nbsp;</p>

<table align="center" cellspacing="1" style="border:1px solid #486090; 
width:98%">
	<tbody>
		<tr>
			<td style="background-color:#486090">Caleb Marshall 
wrote:</td>
		</tr>
		<tr>
			<td style="background-color:#FFFFB0">
			<p>Hello,</p>

			<p>At our lab we are currently in the process of 
migrating more of our systems over to Midas. However, all of our working systems 
are dependent on SBCs with the Tsi-148 chips of which we only have a handful. In 
order to have some backups and spares for testing, we have been attempting to 
get Midas working with some borrowed SBCs (Concurrent Technologies VX 40x/04x) 
with Universe-II chips. The SBC is running&nbsp;CentOS 7.&nbsp;I have tried to 
follow the instructions posted <a 
href="https://daq00.triumf.ca/DaqWiki/index.php/VME-
CPU#V7648_and_V7750_BIOS_Settings">here</a>. The universe-II kernel module 
appears to load correctly, dmesg gives:</p>

			<p>[ &nbsp; 32.384826] VME: Board is system 
controller<br />
			[ &nbsp; 32.384875] VME: Driver compiled for SMP 
system<br />
			[ &nbsp; 32.384877] VME: Installed VME Universe module 
version: 3.6.KO6<br />
			&nbsp;</p>

			<p>However, running vmescan.exe fails with a segfault. 
Running with gdb shows:</p>

			<p>vmic_mmap: Mapped VME AM 0x0d addr 0x00000000 size 
0x00ffffff at address 0x80a01000<br />
			mvme_open:<br />
			Bus handle &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
&nbsp;= 0x7<br />
			DMA handle &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
&nbsp;= 0x6045d0<br />
			DMA area size &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; = 
1048576 bytes<br />
			DMA &nbsp; &nbsp;physical address = 0x7ffff7eea000<br />
			vmic_mmap: Mapped VME AM 0x2d addr 0x00000000 size 
0x0000ffff at address 0x86ff0000</p>

			<p>Program received signal SIGSEGV, Segmentation fault.
<br />
			mvme_read_value (mvme=0x604010, vme_addr=&lt;optimized 
out&gt;)<br />
			&nbsp; &nbsp; at 
/home/jam/midas/packages/midas/drivers/vme/vmic/vmicvme.c:352<br />
			352&nbsp;&nbsp; &nbsp; &nbsp; &nbsp;dst &nbsp;= *((WORD 
*)addr);<br />
			&nbsp;</p>

			<p>With the pointer addr originating from a call 
to&nbsp;vmic_mapcheck within the&nbsp;&nbsp;mvme_read_value functions in the 
vmicvme.c file. Help with where to go from here would be appreciated.</p>

			<p>-Caleb&nbsp;</p>

			<p>&nbsp;</p>
			</td>
		</tr>
	</tbody>
</table>

<p>&nbsp;</p>
    Reply  03 Aug 2023, Caleb Marshall, Forum, Issues with Universe II Driver  
Here is the output:

vmic_mmap: Mapped VME AM 0x0d addr 0x00000000 size 0x00ffffff at address 0x80a01000
mvme_open:
Bus handle              = 0x3
DMA handle              = 0x158f5d0
DMA area size           = 1048576 bytes
DMA    physical address = 0x7f91db553000
vmic_mmap: Mapped VME AM 0x2d addr 0x00000000 size 0x0000ffff at address 0x86ff0000
vme addr: 00000000 
addr: db543000 
    Reply  03 Aug 2023, Konstantin Olchanski, Forum, Issues with Universe II Driver  
> Here is the output:
> 
> vmic_mmap: Mapped VME AM 0x0d addr 0x00000000 size 0x00ffffff at address 0x80a01000
> mvme_open:
> Bus handle              = 0x3
> DMA handle              = 0x158f5d0
> DMA area size           = 1048576 bytes
> DMA    physical address = 0x7f91db553000
> vmic_mmap: Mapped VME AM 0x2d addr 0x00000000 size 0x0000ffff at address 0x86ff0000
> vme addr: 00000000 
> addr: db543000 

I see the problem. A24 is mapped at 0x80xxxxxx, A16 is mapped at 0x86ffxxxx, but 
mvme_read computed address 0xdb543000, out of range of either mapped vme address. ouch.

One more thing to check, AFAIK, this universe-II codes were never used on 64-bit CPU 
before, we only have 32-bit Pentium-3 and Pentium-4 machines with these chips. The 
tsi148 codes used to work both 32-bit and 64-bit, we used to have both flavours of 
CPUs, but now only have 64-bit.

What is your output for "uname -a"? does it report 32-bit or 64-bit kernel?

If you feel adventurous, you can build 32-bit midas (cd .../midas; make linux32), 
compile vmescan.o with "-m32" and link vmescan.exe against .../midas/linux-m32/lib, and 
see if that works. Meanwhile, I can check if vmicvme.c is 64-bit clean. Checking if 
kernel module is 64-bit clean would be more difficult...

K.O.
    Reply  03 Aug 2023, Caleb Marshall, Forum, Issues with Universe II Driver  
I am looking into compiling the 32 bit midas.

In the meantime, here is the kernel info:

3.10.0-1160.11.1.el7.x86_64 

Thank you for the help.
-Caleb
    Reply  04 Aug 2023, Caleb Marshall, Forum, Issues with Universe II Driver  
I can compile 32 bit midas. Unless I am interpreting the linking error, I don't 
think I can use the driver as built. 

While trying to compile vme_scan, most of the programs fail with:

/usr/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-redhat-
linux/4.8.5/../../../../lib/libvme.so when searching for -lvme
/usr/bin/ld: skipping incompatible /lib/../lib/libvme.so when searching for -lvme
/usr/bin/ld: skipping incompatible /usr/lib/../lib/libvme.so when searching for -
lvme
/usr/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-redhat-
linux/4.8.5/../../../libvme.so when searching for -lvme
/usr/bin/ld: skipping incompatible //lib/libvme.so when searching for -lvme
/usr/bin/ld: skipping incompatible //usr/lib/libvme.so when searching for -lvme

with libvme.so being built by the universe-II driver. Not sure if I can get around 
this without messing with the driver? Is it possible to build a 32 bit version of 
that shared library without having to touch the actual kernel module? 

-Caleb
    Reply  04 Aug 2023, Konstantin Olchanski, Forum, Issues with Universe II Driver  
> I can compile 32 bit midas. Unless I am interpreting the linking error, I don't 
> think I can use the driver as built.

I think you are right, Makefile from the Universe package does not build a -m32 version 
of libvme.so. I think I can fix that...

K.O.
Entry  16 Dec 2020, Isaac Labrie Boulay, Forum, Issues building banks. 
Hi all,

I'm currently trying to build events through doing block transfers. The worry was 
that organizing and packaging bank data into an array would produce too much dead 
time causing too many missed events. Trying out that method, I'm running into all 
sorts of issues such as unaligned transfers where the QDC events are unaligned, or 
improperly aligned banks. Giving me a headache.

My question is, if I were to revert back to simple 32 bit read cycles and using 
the fevme.cxx template's method of organizing data before sending them to the 
buffer, what kind of deadtime should I expect? Am I wrong to assume that this 
would result in deadtime at all? I'm using a CAEN V792n 16 channel QDC and the hit 
frequency that I'm using to test is 20kHz.

Thanks.

Isaac
    Reply  16 Dec 2020, Konstantin Olchanski, Forum, Issues building banks. 
> I'm currently trying to build events through doing block transfers.

I am confused by your question. I assume you read a CAEN V792 ADC, but I do not know what VME master you 
use. The restrictions on data alignment come from the VME master.
I am mostly familiar with restrictions of UniverseII and tsi148 PCI-VME bridges.
I think there is no restriction for USB-VME bridges and similar.

Anyhow. Which block transfer do you use? 32-bit block transfer (BLT32)? 64-bit block transfer (MBLT64)? 
(no 128-bit 2eVME/2eSST transfers from the V792). Maybe the "simulated block transfer" (DMA engine uses 
single-word reads instead of block transfer)?

> The worry was that organizing and packaging bank data into an array would produce too much dead time 
causing too many missed events.

Valid concerns.

> I'm running into all sorts of issues such as unaligned transfers where the QDC events are unaligned, or 
improperly aligned banks.

You should not see any problems with unaligned transfers if you give the DMA engine
correct memory addresses as required by the hardware:

- always aligned to 32-bit (4 bytes, last two address bits set to 0)
- aligned to 64-bits for MBLT64 64-bit transfers, this would be the normal case for the V792 (8 bytes, 
last 3 address bits set to 0)
- aligned to 128-bits for 2eVME/2eSST transfers (16 bytes, last 4 bits of address are zero).

You also need to specify correct amount of data to read: number of bytes should be multiple of 4 for 32-
bit transfers, multiple to 8 for 64-bit transfers and multiple of 16 for 128-bit transfers (2eVME/2eSST).

Very often this requires reading "extra" data words. Most VME modules can generate extra pad words to 
align event length to DMA restrictions. Sometimes you need to
enable this in a control register (V792, V1190).

> Giving me a headache.

Me too. MIDAS recently introduced the QWORD 64-bit data type, banks of this type
should have correct alignment for 64-bit VME block transfers. But for 2eVME/2eSST
transfers, I still have to ensure alignment "by hand" (SIS3820, VF48, etc).

With QWORD banks, you need to use bk_init32a() instead of bk_init32().

> My question is, if I were to revert back to simple 32 bit read cycles

Yes, I always test with single-word reads first, with the 32-bit block transfer second and try the 64-bit 
block transfer last.

Sometimes there are unrelated problems (with the VME modules, VME bus, etc, or
with bugs in the frontend, etc) and this approach helps to identify the source
of trouble.

> and using 
> the fevme.cxx template's method of organizing data before sending them to the 
> buffer, what kind of deadtime should I expect? Am I wrong to assume that this 
> would result in deadtime at all? I'm using a CAEN V792n 16 channel QDC and the hit 
> frequency that I'm using to test is 20kHz.

Yes, with asynchronous read using 64-bit block transfer, 20 kHz should be achievable.

The old fevme frontend is based on the mfe.c framework and implementing
async readout requires special contortions. The structure of the new TMFE C++ frontend
class is supposed to make it easier, but I do not have an example TMFE based fevme yet.

P.S. Without using block transfer, your max rate is limited to:

16 channels, 1 word per channel, plus 1 header and 1 footer = 18 words (by luck, 64-bit aligned for 
correct BLT64 block read).

using VME single-word read at 1 us per transfer, 18 us per event = 55 kHz repetition rate.

(you do not say if you have any other VME modules you have to read)

K.O.
    Reply  16 Dec 2020, Isaac Labrie Boulay, Forum, Issues building banks. 
Thanks for the quick reply,

> > I'm currently trying to build events through doing block transfers.
> 
> I am confused by your question. I assume you read a CAEN V792 ADC, but I do not know what VME master you 
> use. The restrictions on data alignment come from the VME master.
> I am mostly familiar with restrictions of UniverseII and tsi148 PCI-VME bridges.
> I think there is no restriction for USB-VME bridges and similar.
> 
> Anyhow. Which block transfer do you use? 32-bit block transfer (BLT32)? 64-bit block transfer (MBLT64)? 
> (no 128-bit 2eVME/2eSST transfers from the V792). Maybe the "simulated block transfer" (DMA engine uses 
> single-word reads instead of block transfer)?

I read a single CAEN V792n QDC, 18 words, and a single CAEN V1190 TDC, 2 channels so 8 words. When I poll, I 
read on every poll_event() and read whatever data is in whatever module (TDC_dataready || QDC_dataready). The 
VME master that I'm using to talk to the modules is a CAEN V1718. I am trying to read data by BLT32. Sorry for 
the confusing question (Can you tell I'm an intern?).

> > The worry was that organizing and packaging bank data into an array would produce too much dead time 
> causing too many missed events.
> 
> Valid concerns.
> 
> > I'm running into all sorts of issues such as unaligned transfers where the QDC events are unaligned, or 
> improperly aligned banks.
> 
> You should not see any problems with unaligned transfers if you give the DMA engine
> correct memory addresses as required by the hardware:
> 
> - always aligned to 32-bit (4 bytes, last two address bits set to 0)
> - aligned to 64-bits for MBLT64 64-bit transfers, this would be the normal case for the V792 (8 bytes, 
> last 3 address bits set to 0)
> - aligned to 128-bits for 2eVME/2eSST transfers (16 bytes, last 4 bits of address are zero).
> 
> You also need to specify correct amount of data to read: number of bytes should be multiple of 4 for 32-
> bit transfers, multiple to 8 for 64-bit transfers and multiple of 16 for 128-bit transfers (2eVME/2eSST).

I am transferring 32-bit words. Transferring 32-bit words should always read multiples of 4 bytes so that's 
good.

> Very often this requires reading "extra" data words. Most VME modules can generate extra pad words to 
> align event length to DMA restrictions. Sometimes you need to
> enable this in a control register (V792, V1190).
> 
> > Giving me a headache.
> 
> Me too. MIDAS recently introduced the QWORD 64-bit data type, banks of this type
> should have correct alignment for 64-bit VME block transfers. But for 2eVME/2eSST
> transfers, I still have to ensure alignment "by hand" (SIS3820, VF48, etc).
> 
> With QWORD banks, you need to use bk_init32a() instead of bk_init32().
> 
> > My question is, if I were to revert back to simple 32 bit read cycles
> 
> Yes, I always test with single-word reads first, with the 32-bit block transfer second and try the 64-bit 
> block transfer last.
> 
> Sometimes there are unrelated problems (with the VME modules, VME bus, etc, or
> with bugs in the frontend, etc) and this approach helps to identify the source
> of trouble.
> 
> > and using 
> > the fevme.cxx template's method of organizing data before sending them to the 
> > buffer, what kind of deadtime should I expect? Am I wrong to assume that this 
> > would result in deadtime at all? I'm using a CAEN V792n 16 channel QDC and the hit 
> > frequency that I'm using to test is 20kHz.
> 
> Yes, with asynchronous read using 64-bit block transfer, 20 kHz should be achievable.
> 
> The old fevme frontend is based on the mfe.c framework and implementing
> async readout requires special contortions. The structure of the new TMFE C++ frontend
> class is supposed to make it easier, but I do not have an example TMFE based fevme yet.
> 
> P.S. Without using block transfer, your max rate is limited to:
> 
> 16 channels, 1 word per channel, plus 1 header and 1 footer = 18 words (by luck, 64-bit aligned for 
> correct BLT64 block read).
> 
> using VME single-word read at 1 us per transfer, 18 us per event = 55 kHz repetition rate.
> 
> (you do not say if you have any other VME modules you have to read)
> 

Okay so transferring 18 + 6 words should give me close to 40kHz repetition rate. That's good news. I will just 
stick to 1 word transfers.

The way that transfers are done in the fevme.cxx requires iterating through 16 word arrays a number of time (3 
times I believe if you include the iterations taking place in v792_EventRead()). Does that not pose a 
significant deadtime concern? 

> K.O.

Thanks again for taking the time to help me out!

Cheers.

Isaac
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