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<== Date ==> <== Thread ==>

Subject: mca R7-0
From: "Mark Rivers" <>
To: <>, <>, <>, <>
Date: Sun, 1 May 2011 15:01:04 -0500

I am getting ready to release mca R7-0.  This release is mainly a rewrite of the SIS3801 and SIS3820 MCS support.  I've appended the release notes below, which are also available here: 

I would appreciate any testing that can be done on the new support before I release it.  I have not had a chance to update the documentation in mca/documentation/Struck.html yet, only the release notes, but I will do that before the final release.  The iocBoot/iocVxWorks/st_SIS3801.cmd and st_SIS3820.cmd files can be used as examples, along with mcaApp/op/adl/SIS38XXTest.adl.

The code can be obtained from the synApps Subversion repository:






mca Release Notes

Release 7-0 (XXX-May-2011)

SIS3801 and SIS320 multi-channel scaler support

The SIS3801 and SIS3820 support has been completely rewritten. In previous releases the driver was "synchronous", meaning that the MCA records blocked while the arrays were read from the FIFO on the VME modules. FIFO reads were done with VME program I/O, which can only do about 1000 32-bit words per ms. This was acceptable if the arrays were small (e.g. 2048 channels) because it only took a few ms to read each array. However, some users were beginning to use very large arrays (e.g. 2,000,000 channels). In this case it took several seconds to read each array. Because the MCA records were synchronous, this blocked execution of other EPICS records and tasks while reading the hardware. This was unacceptable, leading to channel access disconnects and other bad effects.

One way to fix this would be to make the drivers asynchronous, meaning that device support will do the I/O in a separate thread, and the records will not block. This is how other slow drivers for the MCA records work, for example the Canberra AIM and the XIA DXP modules. However, this approach cannot be used with the SIS drivers because they must support the EPICS "scaler" record, and the scaler record does not work properly with asynchronous device suppport.

Instead, the drivers were rewritten so that the FIFO is read out into a driver buffer in a low-priority background thread. When the MCA records process they now just read the data from this driver buffer using a memcpy() call, which is very fast. Furthermore on the 3820 the driver now reads the FIFO using DMA over the VME bus. This yields a factor of 10 improvement in speed, over 40MB/s, compared to 4MB/s with program I/O.

The new drivers have excellent performance with very large arrays, and arrays with more than 10 million elements can now be used if the VME CPU has sufficient memory. For example, a test was done with the following configuration: 

*	SIS3820 module 
*	MVME 5100 CPU with 512MB of memory 
*	vxWorks 5.4.2 with Andrew Johnson's BSP with DMA support 
*	2 active inputs 
*	10,000,000 channels per waveform 
*	2 waveform records 
*	Internal channel advance 
*	1 microsecond dwell time 
*	ReadAll.SCAN = Passive 

The theoretical time for this acquisition to complete is 10 seconds. The following is the output from the EPICS "camonitor" program on a Linux client looking at the Acquiring PV, and the first 2 channels of each waveform record: 

    >camonitor -tc -#2 SIS:3820:mca1 SIS:3820:mca2 SIS:3820:Acquiring 
    SIS:3820:Acquiring             (2011-05-01 11:19:35.050808) Acquiring 
    SIS:3820:mca1                  (2011-05-01 11:19:46.017134) 2 50 50 
    SIS:3820:mca2                  (2011-05-01 11:19:46.017223) 2 0 0 
    SIS:3820:Acquiring             (2011-05-01 11:19:46.017264) Done 

So the time between when acquistion started and when the client received the data and the Acquiring=Done status was 10.97 seconds. There is thus less than 1 second of overhead in collecting 2 waveforms of 10,000,000 elements each, which is 80MB of data. 

The following features have also been added to the drivers (thanks to Ulrik Pedersen from DLS for the initial implementation of several of these):

*	It is no longer necessary to use the MCA record for the arrays. The standard EPICS waveform record can now be used instead if that is desired. The performance is somewhat better with the waveform record, because it has less overhead when it reads the arrays, not needing to perform ROI calculations, etc. The example startup scripts contain commands for both MCA and waveform records 
*	There is a new PV to perform a software channel advance. (Note that channel advance is called LNE in the SIS manuals). This PV can be processed at any time, and works in both internal and external channel advance modes. 
*	There is a new PV to control whether the driver does an initial software channel advance when acquisition is started, or whether the module does not start counting until the first internal or external channel advance signal arrives. Previously this option was only configurable in the startup script for the 3801, and was not available for the 3820 at all. 
*	There are new PVs to control the input and output modes. These control the functionality of the 4 input control signals and the 4 output control signals. There were previously only configurable in the startup script, while they can now be changed at run-time. 
*	There is a new PV to control the channel 1 source, i.e. whether it uses the internal clock (25MHz on 3801, 50MHz on 3820), or an external pulse input. This was previously only configurable in the startup script. 
*	There is a new PV to control the user-defined LED on the module, and on the 3820 this is linked to a user-defineable binary output signal on a control output. 
*	There is a new PV to select which input is routed via the MUX to one of the output control signals on the 3820. 
*	There are new PVs that reflect the current acquisition mode (MCS or Scaler), the model number (3801 or 3820), and the firmware version. 
*	There is a new PV that displays the current channel number being acquired. This PV is I/O Intr scanned, and reflects the current value, whether or not the MCA or waveform records are being periodically processed during acquisition. 
*	The elapsed time PV is now also I/O Intr scanned, and reflects the current value, whether or not the MCA or waveform records are being periodically processed during acquisition. 
*	It is no longer necessary to periodically process the MCA records during acquisition to obtain status updates, so the StatusAll PV has been removed. 
*	The ReadAll PV can be periodically processed during acquisition to read the arrays into the MCA or waveform records. However, this is optional, and if this record is Passive then the arrays will still be read into these records as soon as acquisition completes. For highest performance with very large arrays this record should be Passive. 
*	In previous releases the database file (e.g. Struck32.db) contained the logic to process all of the MCA records when acquisition completed and to do other coordination tasks for the multiple MCA records. This required having multiple databases depending on how many MCA records (e.g. active inputs) were being used, and 8 and 32 input versions were included in the distribution. If an application demanded a different number of inputs (e.g. only 2 inputs with a very large number of channels) then the database needed to be customized. In the new release this logic is no longer in the database; rather it is contained in a very simple SNL program that must be run. This allows a single simple database to be used, no matter how many MCA or waveform records are being used. 
*	There is now logic in the database to disable Autocount mode in the scaler record when MCS data acquisition is started. This can prevent the interference that has been a problem in the past if Autocount started the scaler while MCS acquisition was in progress. However, this logic is not bullet-proof depending on exact timing, so it is still recommended to manually turn off autocount before starting MCS acquisition. 
*	The performance of the Erase operation has been significantly improved for large arrays. Previously the entire buffer, which could be many megabytes, was erased when any MCA record did the erase operation. This has been fixed so that it is only done once, and not 32 times if there are 32 MCA records. 

With the many improvements and new features in the drivers the amount of code has actually decreased in R7-0 compared to previous releases. The following table compares the size of the driver code and databases between R-7 and R6-12-15. 

Size of driver source code 
R6-12-5	 R7-0	
File 	Lines 	File 	Lines 
devStr7201.c	 264	 116	
devScalerST7201.c	 326	 apsLib.h	 58	
drvMcaSIS3820Asyn.c	 1689	 drvSIS3801.cpp	 731	
drvMcaSIS3820Asyn.h	 285	 drvSIS3801.h	 210	
drvSTR7201.c	 812	 drvSIS3820.cpp	 1017	
drvSTR7201.h	 38	 drvSIS3820.h	 225	
mcaSIS3820Register.c	 62	 drvSIS38XX.cpp	 542	
mcaSSTR7201Register.c	 49	 drvSIS38XX.h	 164	
sis3820.h	 240	 sis3820.h	 240	
N.A.	 -	 vmeDMA.h	 53	
TOTAL 	3765 	TOTAL 	3356 
Size of databases	
Struck32.db	 623	 SIS38XX.template	 303	
Struck8.db	 215	 SIS38XX_waveform.template	 9	
STR7201scaler.db	 241	 N.A.	 -	
SIS3820.db	 7	 N.A.	 -	
TOTAL 	1086 	TOTAL 	311 

The driver is thus 10% smaller than in the previous release. This is because in the previous release the SIS3801 support had device-specific device support for the scaler and MCA records (which were not based on asyn), and the SIS3820 driver used basic asyn support, rather than asynPortDriver. In the new drivers the standard asyn device support for the scaler record (from the std module), the mca record (from the mca module), and the waveform record (from the asyn module) are used, there is no custom device support. Moreover, there is a base class, drvSIS38XX.cpp, which is implements the functions common to both the SIS3801 and the SIS3820. SIS38XX is derived from asynPortDriver which handles much of the standard asyn code, and SIS3801.cpp and SIS3820.cpp are derived from SIS38XX.cpp.

The SIS3801 and SIS3820 support in R7-0 is not backwards compatible with previous releases. IOC startup scripts must be changed, and the medm screens are different. However, the PVs that most clients like the sscan record, SPEC and IDL are using have not changed, so those clients should not need to be modified.

MCA record, MCA device support and MCA driver changes

Previously the MCA record sent the following messages (defined in mca.h) to device support:

*	mcaChannelAdvanceInternal 
*	mcaChannelAdvanceExternal 
*	mcaModePHA 
*	mcaModeMCS 
*	mcaModeList 

Thus, it was sending a separate message for each type of channel advance and each type of acquisition mode. This was inconvenient for drivers and device support, and was not consistent with the way that other parameters were handled. This was thus changed to:

*	mcaChannelAdvanceSource 
*	mcaAcquireMode 

where the value passed to device support in the message now specifies what type of channel advance source or acquisition mode is being requested. Similarly the strings defined in drvMca.h that are used by device support and drivers to define the asyn drvInfo value have had the same changes. The driver now receives a single command to change the acquire mode for example, and the value passed on the aysnInt32 interface specifies which acquire mode is being requested. This makes the interface more extensible. All existing drivers in synApps have been modified to use the new interface.

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