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Ethernet Connection impact in CPU scan Time

Created by: Maha at: 5/12/2010 10:44 AM (5 Replies)

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5/12/2010 10:44 AM	Rate (0)
Maha Posts: 118 Rating: (4)	Hi all, I have few question related with Ethernet connection on CPU scan Time. I know that ethernet connection will make some increase in CPU scan Time. Question1: How to calculate Netpro connection impact in CPU Scan Time? Question 2: Number of connections in Ethernet will make any impact on CPU processing Time? How to calculate Question3: Number of bytes used in ethernet communication will make any impact on CPU scan time? How to Calculate?
Maha Posts: 118 Rating: (4)
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5/12/2010 12:21 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 12/5/2024 Posts: 1548 Rating: (538)	I think to make an estimate, more information is required. How many connections have you configured in Netpro? What type are the connections (e.g. TCP, UDP, ISO etc.)? Are the active or passive establisment? What is connected to the connections / what is the function of the connections (e.g. OS, modbus TCP etc.)? How much data is being sent / received over the connections and how often is it sent / recieved (e.g. number of OS tags, amount of modbus registers etc.)? What FC/FB are you using in the AS to send / receive that data (e.g. AG_LSEND / AG_LRECV etc.)? I know there is a setting in the CPU configuration that reserves and amount of CPU time dedicated to just handling the comms. It is called the "Scan Cycle Load from Communication" and is accessed via the "Cycle/Clock Memory" tab of the CPU properties. The default value is 20%. So 20% of the CPU cycle time is dedicated to solely handling the comms. The online help text for this setting has some useful information as to how this affects the CPU scan cycle time.
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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5/13/2010 3:54 AM	Rate (0)
Maha Posts: 118 Rating: (4)	smiffy I think to make an estimate, more information is required. How many connections have you configured in Netpro? What type are the connections (e.g. TCP, UDP, ISO etc.)? Are the active or passive establisment? What is connected to the connections / what is the function of the connections (e.g. OS, modbus TCP etc.)? How much data is being sent / received over the connections and how often is it sent / recieved (e.g. number of OS tags, amount of modbus registers etc.)? What FC/FB are you using in the AS to send / receive that data (e.g. AG_LSEND / AG_LRECV etc.)? I know there is a setting in the CPU configuration that reserves and amount of CPU time dedicated to just handling the comms. It is called the "Scan Cycle Load from Communication" and is accessed via the "Cycle/Clock Memory" tab of the CPU properties. The default value is 20%. So 20% of the CPU cycle time is dedicated to solely handling the comms. The online help text for this setting has some useful information as to how this affects the CPU scan cycle time. minimum 20 number of connections planned for each CPU. ISO on TCP will be used. all will be passive connections. functions is just sending data about the conveying materials and receving the next control from Server (PC). data range will be minimum of 300 bytes. as of now decided to use AG_SEND/AG_RECEIVE. I have seen in CPU properties, what is that 20% of the CPU cycle time is dedicated to solely handling the comms?
Maha Posts: 118 Rating: (4)
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5/13/2010 3:29 PM	Rate (1)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 12/5/2024 Posts: 1548 Rating: (538)	Have you read the help file? I have attched it for you. I originally thought that the cycle time would increase / decrease depending on the number of connections and the traffic going over these connections. Looking at the help file, suggests that this is the case up to a point. The "Scan Cycle Load from Communication" setting sets the maximum amount of CPU time provided for handling communications jobs. If the required amount of CPU time to process the communications jobs is less that this setting, then the remainder will be used for processing the runtime code. This is the way I interpret the help file: If all communications jobs cannot be processed by amount of CPU time allocated to communications processing in a cycle (20% with the default setting), the communications jobs will need additional cycles to complete. So the CPU loading for communications will vary, but can never be greater than this setting. So this setting must be chosen carefully so that there is enough time alloacted to process the worst case communications load. Not too sure how you would go about trying to work out this setting. I suppose you would have to find out how fast the AS functions process the data (bits/bytes per second) and multiply that by the amount of data for each connection. Then add all these up for each connection. This would give you a time value. Then this could be compared with the required minimum scan time, and the % needed for communications could be ascertained. Attachment Scan Cycle Load from Communication.pdf (438 Downloads)
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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5/14/2010 3:12 AM	Rate (0)
Maha Posts: 118 Rating: (4)	Thank You Very Much smiffy. Its nice explanation to get some good idea. I will try to calculate and set the CPU properties for communication load.
Maha Posts: 118 Rating: (4)
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5/14/2010 4:16 AM	Rate (0)
Maha Posts: 118 Rating: (4)	Maha minimum 20 number of connections planned for each CPU. ISO on TCP will be used. all will be passive connections. functions is just sending data about the conveying materials and receving the next control from Server (PC). data range will be minimum of 300 bytes. as of now decided to use AG_SEND/AG_RECEIVE. I have seen in CPU properties, what is that 20% of the CPU cycle time is dedicated to solely handling the comms? Hi, One more clarification, on based on my above details, which function (SEND/RECEIVE) i can use it and how i can justify that one is best.
Maha Posts: 118 Rating: (4)
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