RE: RE: RE: Use of waveform records

["Mark Rivers" <rivers@cars.uchicago.edu>]

This will not work:
 
record(calc, "calc1") {                                                                
    field(INPA, "0xc1480000")                                                          
    field(INPB, "-12.5")                                                               
    field(CALC, "A")                                                                   
    field(SCAN, "1 second")                                                            
}

Because the constant in INPA constant 0xc148000 will be interpreted as an integer, not a bit pattern for a double, and 0xc148000 is the integer 3242721280.
 
>From Python:
>>> 0xc1480000
3242721280L

Mark

 
________________________________

From: tech-talk-bounces@aps.anl.gov on behalf of Silver
Sent: Sat 11/29/2008 7:48 PM
To: tech-talk
Subject: Re: RE: RE: Use of waveform records



hi, Mark:

  I have done this as same as your suggestions before I found this topic. also I tried to just use records to implement it. it's easy to seperate a 32 bit data to two 16 bit data in record, but I failed to combine two 16 bit data to a 32 bit float in db file. for example: the float -12.5 is stored as 0xC1480000. when it's transfered, IOC get 0xc148 and 0x0000. how to convert it back to -12.5?
or see this record:
record(calc, "calc1") {                                                                
    field(INPA, "0xc1480000")                                                          
    field(INPB, "-12.5")                                                               
    field(CALC, "A")                                                                   
    field(SCAN, "1 second")                                                            
}
caget will get the value 3.24272e+09. In fact, it's knowledge about record, a bit far from modbus driver.
thanks for your reply.

======= At 2008-11-29, 23:06:38 you wrote: =======

>You could use a 2-element waveform to read the 2 16-bit words, and then use a gensub to combine these into a 32-bit float.  You will need to worry about byte order, since that might not be the same on the PLC and the IOC host.  The Modbus specification only describes 16-bit words, anything done with floats or other data types is vendor-specific.
>
>Mark
>
>
>________________________________
>
>From: tech-talk-bounces@aps.anl.gov on behalf of marco_hair
>Sent: Sat 11/29/2008 8:47 AM
>To: tech-talk
>Subject: Re:RE: Use of waveform records
>
>
>hi,Mark:
>
>I searched the tech-talk and found this topic before. My situation is on the contrary: the device need to send a 32 bit float to IOC. since modbus tcp only support 16 bit data, this 32 bit float will be seperated to two 16 bit data and sent. I can use gensub to implement it. If I want to just use record to implement it, how to do this? would you give me some suggestions? Surely I am using your latest modbus tcp device.
>Thanks a lot in advance.
>
>?2007-10-16,"Mark Rivers" <rivers@cars.uchicago.edu> ??:
>
>Hi Dominique,
>
>I just put together a test database to convert a 32-bit ao record to 2 16-bit ao records.  Here is the database:
>
>record(ao, "test:ao") {
>    field(FLNK, "test:calcLSW.PROC")
>}
>
>record(calcout, "test:calcLSW") {
>    field(INPA, "test:ao.VAL  NPP NMS")
>    field(CALC, "A&65535")
>    field(OUT, "test:aoLSW")
>    field(FLNK, "test:calcMSW.PROC")
>}
>
>record(calcout, "test:calcMSW") {
>    field(INPA, "test:ao.VAL  NPP NMS")
>    field(CALC, "(A>>16)&65535")
>    field(OUT, "test:aoMSW")
>}
>
>record(ao, "test:aoLSW") {
>}
>
>record(ao, "test:aoMSW") {
>}
>
>I then tested this database with various 32-bit input values to test:ao, and looked at the 16-bit output values in test:aoLSW and test:aoMSW.
>
>Here are the results:
>
>corvette> caput -s test:ao "0x1"
>Old : test:ao                        2.41592e+09
>New : test:ao                        1
>corvette> caget test:ao test:aoLSW test:aoMSW
>test:ao                        1
>test:aoLSW                     1
>test:aoMSW                     0
>
>corvette> caput -s test:ao "0xffff"
>Old : test:ao                        1
>New : test:ao                        65535
>corvette> caget test:ao test:aoLSW test:aoMSW
>test:ao                        65535
>test:aoLSW                     65535
>test:aoMSW                     0
>
>corvette> caput -s test:ao "0x7fffffff"
>Old : test:ao                        2.68435e+08
>New : test:ao                        2.14748e+09
>corvette> caget test:ao test:aoLSW test:aoMSW
>test:ao                        2.14748e+09
>test:aoLSW                     65535
>test:aoMSW                     32767
>
>corvette> caput -s test:ao "0x8fffffff"
>Old : test:ao                        2.14748e+09
>New : test:ao                        2.41592e+09
>corvette> caget test:ao test:aoLSW test:aoMSW
>test:ao                        2.41592e+09
>test:aoLSW                     0
>test:aoMSW                     32768
>
>I conclude that the database works OK until the most-significant bit in the 32-bit test:ao record is set.  The database then fails, probably because the calc parser is converting to a 32-bit signed integer, rather than unsigned.  For numbers up to 0x7fffffff ( 2147483647 decimal) it works OK.
>
>Mark
>
>
>
>
>
>From: Touchard Dominique [mailto:touchard@ganil.fr]
>Sent: Thursday, October 11, 2007 3:46 AM
>To: Mark Rivers
>Cc: tech-talk@aps.anl.gov
>Subject: Re: Use of waveform records
>
>
>
>
>Mark Rivers a ?rit :
>Hi Dominique,
>
> 
>Perhaps I discovered a  modbus driver "feature"  ?
>I created one modbus number 4 read function which read 11 bytes. I tested three waveform input records.
>These three records read 3 different values on different offsets. These 3 records read the offset 0 ???!!!
>   
>
>That is the documented behavior for asynInt32Array support.  Look at
>
>http://cars9.uchicago.edu/software/epics/modbusDoc.html#EPICS%20device%20support
>
>in the section on asynInt32Array support.  You will see that the "offset" field is NA (not applicable) for all Modbus functions for asynInt32Array. 
> 
>You are totally right. Thanks. I'll take back my glasses. ;-)
>
>
> 
>About ai/ao records, I will need to write and read float values with the Modbus driver.
>I saw integer examples. Ai/ao examples work with asyn32int type.
>Did you test asynFloat64 values ?
>Do I have to use waveform records (ie 32bits : sign:1bit exponent:8bits fraction:23bits) ?
>   
>
>Float values are not a standard Modbus data type; they are not documented in the Modbus standard.  Again, because they are more than 16 bits long, they require multiple Modbus words.  I think you need to do the same thing you do for 32-bit integers, i.e. use a calc, Gensub or SNL code to convert to two 16-bit integers and then use two longout records or a waveform record.
>
> 
>I have a beginner's question : does the bit left shift work like C code?
>Can I write something like A << 16 in the calc expression?
>   
>
>Yes, that is documented under Bitwise Operators here:
>http://www.aps.anl.gov/epics/EpicsDocumentation/AppDevManuals/RecordRef/Recordref-13.html#HEADING13-0
>
> 
>I tried to convert the 32 bit integer value into 2 16 bits values with a calc record.
>Because of float conversion troubles, I don't  get through to get the right values.
>   
>It seems to me like it should work, since I think any 32-bit integer can be represented exactly in a 64-bit double.  Can you send an example that did not seem to work?
> 
>I broke the EPICS database to make a SNL code. I haven't got any example. I tried to use the 0x0000FFFF bit mask. I thought this value was converted  in a float value and the bitwise operation didn't give the right result when it was converted back to an integer.  The 0x0001000 bit mask worked. Perhaps I made a mistake.
>
>I will tried again with two shifts (one 16 bits left shift to lose MS bits and and one right to give back the right bit position).
>
>Thanks again for your help.
>Dominique.
>
>
>Mark
>
>
>
>________________________________
>
>From: Touchard Dominique [mailto:touchard@ganil.fr]
>Sent: Tue 10/9/2007 3:50 AM
>To: Mark Rivers
>Cc: tech-talk@aps.anl.gov
>Subject: Re: Use of waveform records
>
>
>Hi Mark,
>
>Thanks for your answer. I agree with you. We mustn't modify the driver.
>
>The power supply could work with two longout records. In the future, I will need to know how to work with a waveform, an SNL or Gensub code. So I decided to try these tools. I have written an SNL code which does this conversion. I know this is not the best solution. I will try a gensub record soon.
>I tried to convert the 32 bit integer value into 2 16 bits values with a calc record. Because of float conversion troubles, I don't  get through to get the right values. I have a beginner's question : does the bit left shift work like C code? Can I write something like A << 16 in the calc expression?
>
>Perhaps I discovered a  modbus driver "feature"  ? I created one modbus number 4 read function which read 11 bytes. I tested three waveform input records. These three records read 3 different values on different offsets. These 3 records read the offset 0 ???!!!
>
>So I decided to create only one input waveform which read the whole bytes. It works fine. At present, the SNL code converts the values.
>
>About ai/ao records, I will need to write and read float values with the Modbus driver. I saw integer examples. Ai/ao examples work with asyn32int type. Did you test asynFloat64 values ? Do I have to use waveform records (ie 32bits : sign:1bit exponent:8bits fraction:23bits) ?
>
>Thanks for your help.
>
>Dominique.
>
>
>Mark Rivers a ?rit :
>
>One thought on this.
>
>Because you must do 2 Modbus operations to write a 32-bit value with
>Modbus, I suspect that the power supply only updates the value when you
>write one of the 16-bit words, i.e. either the most-significant or
>least-significant 16 bits.  You should read the documentation to find
>out which one actually updates the power supply and make your database
>write that value last.  Otherwise you will get a momentary garbage
>output if you do it in the wrong order.
>
>Mark
>
>
> 
>
>-----Original Message-----
>From: tech-talk-bounces@aps.anl.gov
>[mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Mark Rivers
>Sent: Friday, October 05, 2007 11:23 AM
>To: Touchard Dominique; tech-talk@aps.anl.gov
>Subject: RE: Use of waveform records
>
>Hi Dominique,
>
>Sorry for the delay in replying to this, I was on vacation.
>
>I think an easier solution to this problem is to use 2 calc records to
>convert the 32-bit integer to 2 16-bit integers, and write
>those to the
>Modbus driver using function 6.  Then you don't have to write any C
>code, just a simple database.
>
>PowerSupply (longout) -> calc1 (16 LSB) -> longout1 -> Modbus
>                      -> calc2 (16 MSB) -> longout2 -> Modbus
>
>I don't recommend modifying the driver, because a 32-bit
>integer is not
>a standard Modbus data type, and we could end up with all sorts of
>modifications for non-standard data types.
>
>Mark
>
>
>   
>
>-----Original Message-----
>From: tech-talk-bounces@aps.anl.gov
>[mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of
>     
>
>Touchard Dominique
>   
>
>Sent: Wednesday, September 19, 2007 8:44 AM
>To: tech-talk@aps.anl.gov
>Subject: Use of waveform records
>
>Hi,
>
>we are working on/with the Epics modbus tcp driver written by Mark
>Rivers. We need to write a 32 bits integer value in a power supply
>command control interface.  First we thought to write an asyn32Int
>record with the number 6 modbus function.  Immediatly, we
>     
>
>saw that the
>   
>
>driver uses the number 6 modbus function which works only on
>a 16 bits word.
>
>After reading the Modbus Driver Support documentation, we
>     
>
>saw that we
>   
>
>have to use a two value length waveform record.
>
>First question : is this correct ?
>
>Second question : do we have to use the gensub record to manipulate
>values inside a waveform record ? In this case, is there any example
>that shows how to do this ? Could somebody send us an example
>on this ?
>
>Third question : Is a bad idea to modify the modbus driver
>     
>
>in the goal
>   
>
>to write a asyn32Int 32 bits integer record with the 
>     
>
>number 16 modbus
>   
>
>function ?
>
>Thanks for your help .
>
>Dominique Touchard.
>
>
>     
>
>   
>
> 
>
>
> 
>
>
>________________________________
>
>?????,??????????? <http://www.yeah.net/> 

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Best regards                            
Geyang 2008-11-30