Author: admin

Every VSCP device have registers. Registers abstract the settings for any device. Actually a non VSCP device can have a driver that abstract the devices actual setup, whatever it is, into registers.

So what is a register? In VSCP it’s just a byte wide position that can be read or written. Hence to configure a device one simply write registers, to find out the configuration of a device one simply read registers. Two simple operations. Read and write a byte.

Registers is divided in two types. User registers and standard registers. The standard registers is you will find at the same location on every device, that is  in position 80-255 on level I devices and at 0xffffff80 – 0xffffffff on Level II devices.

Standard registers contain information about a device.  The most important information you can find here is the 16-byte GUID which is a globally unique id for the device and the MDF URL which locates the Module description file. You can find firmware version, alarm status and a lot of other information here as well (more info here) .

As the standard registers is at the same location on every device and they always have the same type of content they are easy to use without any more information. The user registers on the other hand can contain anything the maker of the device want them to contain. Actually we call the registers a register abstraction model as they often model a more complex setup that may look like it needs more than just a bunch of 8-bit registers.

For a level I device there are 128 user registers available in the range 0-127. But this register space is also paged into 65535 pages.  Level II device use 0-0xffffff80 for user registers.

As the standard registers can contain anything there is a need for a description on their content. This information is available in the MDF (Module Description File). This XML files location is pointed out in the standard register space and can be fetched by software that need to configure the device. The pointer is a standard URL so the file usually is located on a standard web server.

You can read about the full content of the MDF here.  An example real life MDF is here.

The register content of a device is specified in the MDF. Typically a record looks like this

<reg page="0" offset="11" bgcolor="0xFFFFCC">
<name lang="en">Relay 1 control register</nam>      <description lang="en">The relay control bits enable/disable intelligent relay functionality:\n
Bit 0 - Enable pulse.\n
Bit 1 - If set: Alarm sent when protection timer triggers.\n
Bit 2 - Protection timer enable.\n
Bit 3 - Send On event when relay goes to active state.\n
Bit 4 - Send Off event when relay goes to inactive state.\n
Bit 5 - Send Started event when relay goes to active state.\n
Bit 6 - Send Stopped event when relay goes to active state.\n
Bit 7 - If set to one the relay is enabled.\n
</description><access>rw</access><bit pos="0" default="false"><name lang="en">Reserved</name><description lang="en">This bit is reserved</description></bit><bit pos="1" default="false"><name lang="en">Protection alarm</name><description lang="en">If set: Alarm sent when protection timer triggers.</description></bit><bit pos="2" default="false"><name lang="en">Protection timer enable</name><description lang="en">
If set: Protection timer is enabled and will deactivate relay channel when the timer times out.
</description></bit><bit pos="3" default="false"><name lang="en">On event on activate enable</name><description lang="en">
If set: An on event will be sent when the relay is turned on.
</description></bit><bit pos="4" default="false"><name lang="en">Off event on deactivate enable</name><description lang="en">
If set: An off event will be sent when the relay is turned off.
</description></bit><bit pos="5" default="false"><name lang="en">Started event on activate enable</name><description lang="en">
If set: A started event will be sent when the relay is turned on.
</description></bit><bit pos="6" default="false"><name lang="en">Stopped event on deactivate enable</name><description lang="en">
If set: A stopped event will be sent when the relay is turned off.
</description></bit><bit pos="7" default="false"><name lang="en">Enable relay</name><description lang="en">
Set this bit to make the relay controlable.
</description></bit></reg>

In this case a description of the bits in a register and how they make the device behave as they are set or cleared.  This register is at location 11 on page 0, usually written as 0:11.

Note that we can reach this level of abstraction with a protocol that have only two operations, read and write, it’s hard to think of a simpler protocol than that.

The intended user of the MDF is a configuration software. This piece of software read the MDF location from the device, download it from the server, parse it, and can then help a user to set up a device. Good thing is that one piece of software works for all devices. Later we will explain the wizards that are available in the MDF which makes this even more useful.

Abstractions

A register is an 8-bit location as we said. Now how about storing things, like floating point value, that does not fit in an 8-bit location. Well the answer is simple of course. Store them in multiple 8-bit locations.

To describe this abstractions are used. Abstractions sit on top of registers and specify how higher end types such as integers, strings, floating point values are stored in register space. So a higher end software usually does not bother with registers it instead  work with the high level types it usually deal with.

An example from the same MDF we sampled before

<abstraction type="short" default="0" page="0" offset="18" bgcolor="0xCCFFFF"><name lang="en">Relay pulse time register for relay 0</name><description lang="en">
This is the pulse time for the each relay expressed in seconds.
This can be used to have a relay turn on and off with a certain
preset interval. The min pulse time is 1 second and the max time
is 65535 seconds which is about 18 hours. Set to zero (default)
for no pulse time i.e. the relay will be steady on/off.\n\n
To start a pulse sequence first write the pulse time to this
register and then write 2 to the relay status register to start
the output. The pulse train is terminated by writing on or off
(1 or 0) to the relay status register.\n
</description><access>rw</access></abstraction>


show an integer that has its MSB at pos 0:18 and it’s LSB at 0:19 (Everything in register space is stored MSB first)

Software tools  like VSCP Works (available in the  VSCP & friends package) can handle configuration of any device. Some web-based tools is on the way to do the same.

There is no need for things to be more complicated.

 

 

Yes I know. It’s all about the cloud nowadays. Every device should post their data up to the cloud and allow themselves to be controlled from the cloud. So I will talk about autonomy of a VSCP setup today. Well I know. It’s kind of the opposite to the cloud model as no cloud is needed. But wait, don’t go away, you can have the cloud and autonomy at the same time. Promise.

VSCP is an event bases system. Events are sent by nodes when things happen. The node that originates the event does not care if there is one or two or three receivers. It just originate the event for anyone to receive (must-be-in-the-cloud people: yes the event can be sent up into the cloud).

So another node receive this events, find it interesting, and do something with it. For example if the event sent was CLASS1.CONTROL, Type=TURN-ON (the standard event to turn things on) the receiving node will turn the thing(s) it is supposed to turn on and send CLASS1.INFORMATION, Type=ON (the standard event to tell that something has been  turned on) to tell interested parties that it has turned on a device.

This is typically how the VSCP event system work. An event is sent out and if something happens at a point and a receiving device  take interest in the event, this device also sending out an event telling the system it did something.

The ping-pong mechanism described above where a reply is sent when something is turned on can be used to validate that the expected operation actually has been carried out.

(Must-be-in-the-cloud people: yes the event can come from the cloud and the “response” can go to the cloud).

Well most systems around typically have a server in the system (or a server in the cloud). VSCP does not need one (but CAN have one). Because when a VSCP system is configured it behaves like an autonomous system. All this is possible because of the decision matrix (DM) that can be implemented  in a VSCP node..

The decision matrix

We will only discuss the Level I decision matrix here.  Made for low-end devices, The Level II works mostly the same.

The decision matrix is a 8-byte entity and a device can have zero or more rows in its matrix.  The purpose of the DM is to say

When an event of a certain kind comes in do something.

And the “do something” part of a decision matrix row is called an action. Take a look at the Paris Relay module for some action samples. This is typical for all modules. It has a few well-defined things it can carry out. In the case of the Paris relay module  turn on a relay, turn of a relay and so on.

As the DM looks the same on all VSCP devices it is easy to make a user interface that configures it

1. Let the user decide which event(s) should trigger the action.
2. Select from where the event should come.
3. Select what action should be performed.

Same for every device.

When this is configured  for a devices it will work  autonomous from that point on. Incoming event’s will be feed through the DM of the device and if a match is found the action will be performed.

No server needed.

 

 

Today’s topic is measurements.

Abstract: We show why a well-defined binary datagram content is an advantage over a textual content for measurement data on a wire.

When you see

42

you see two Arabic numbers and probably guess it’s a number in the decimal system. So it’s 40 + 2. But if you are on the receiving end of a communication line what is 42 then? Does it mean anything to you?

Well it could be anything. If the sender sent this number 42, as a temperature you don’t know that it is a temperature  on the receiving end without further information sent or it must be sent on  a channel dedicated for just temperatures. Also you don’t know the unit without more information added. The temperature could be expressed in Kelvin, Fahrenheit or Celsius or even some of the other possible units that are used around the globe.

Still this is how most measurement values are sent. Sometime with adding information like

Temperature: 42 Kelvin

often all packed in XML or JSON envelopes and in text form. Alternatively you will find manifests by packed with the measurement data, big ones, with lots of information and options. Always in textual form.

All this is good and fine for higher end nodes. They have the memory to handle the conversions, the power to do the translations fast. No problem. But for sensor it gets a bit stupid. They are often cost sensitive devices and the processing power will therefore be lower and parsing and memory usage should be kept low. It’s just plain stupid to use high level structures on this level.

The VSCP solution

In VSCP, measurements, like everything else, is identified by a class and a type. There are a few different classes available that handle measurements, but  let us look at the lowest end form here, made to make it easy for small devices to handle this kind of information in a resource efficient still safe way.

The measurement types in VSCP is fetched from the SI system. So all measurement type used in science and engineering is there and is so in a standardized form. Some examples

• Temperature: Class=10 Type=6
• Frequency: Class=10, Type=9
• Pressure: Class=10 Type = 12

you get the picture. You have them all specified here.

All measurements in the SI system have a default units. For temperature  this unit is Kelvin. But people are used to use the more everyday common  Fahrenheit and Celsius. This is true for all other measurements to, so in addition to the class and type to define which measurement is sent VSCP also send which unit this measurement is in. For the low-end devices, four well-defined unit types  is available for each measurement type.  For temperature unit = 0 is Kelvin (zero is always the SI unit), unit=1 is Celsius, unit=2 is Fahrenheit.

Last the format of the data is specified and some other information is also available which we will not go into here (full info is here).

The end result is a very compact measurement record that contain all relevant information. In this case 42 degrees Celsius is packed in seven bytes. Perfect for slow communication lines like RF.

The advantages of this format is

• Small packets with all needed information specified.
• Easy to handle by a low en device.
• Unit and type is always well specified.
• Value coding is always well specified.
• A unified format means uniform handling.

The uniform handling is interesting. This means that one solution can be used to, for example,  draw diagrams for all types of measurements, same for statistical analysis or other analysis or just handling data. Well you get it. A big time and resource saver and no more stupid mistakes (making us miss Mars).

Sync

VSCP is not specially designed to be used in real-time systems. Still if we talk about milliseconds and 10th of microseconds it is usable.

For Level II events in VSCP, which  have a timestamp in the package, this is no problem. Here we have microsecond resolution. But for low-end links the over head of a Level II event may be too much.

Level I events does not have a timestamp in the package. They are time stamped when they are received instead. This may not be enough in some situations.

Solution 1

The sync event (class=30, Type=26) is perfect if you want to  synchronize measurements from several remote modules. Send the sync event on timed occasions and the nodes will respond in a synchronized fashion.  You can timestamp them from the time you sent out the sync, optionally taking in to account the round trip time.

Solution 2

Instead of sync a node that send measurements can send a time event (Class=10, Type=4), using unit= 0 the timestamp can use millisecond resolution

OK that was all for today.

 

Thanks for supporting VSCP (you now who you are). I really appreciate the contributions received after my last call out.

THANKS!