User`s guide
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Tasker – AT91SAM7X Tutorial
V1.4
uTaskerV1.4_SAM7X.doc/0.03 20/36 31.07.2009
They have not yet been committed to memory and the previous setting can be returned by
clicking on “Reset changes”.
Once you are sure that the modifications are correct, they are saved to flash memory by
clicking on “Save changes”. This will cause also a reset of the device after a delay of about 1
second and it will be necessary to establish a new connection to the device using its new
settings and validate the changes.
So why make it so complicated? Well it is simply to be sure that you have not modifying
something which will render the device unreachable. For example, you may have changed its
Ethernet speed from 100M to 10M although it is connected to a hub which only supports
100M and, to make matters worse, the device is not simply sitting on your office desk at
arm’s length but is at a customer’s site several hours drive away. It would be a nasty
situation if you had just lost contact with the equipment and have to somehow get it back on
line although everyone at the customer’s site has already left for a long weekend…
So this is where the validation part comes in. After the reset, the device sees that there are
new settings in memory but also that these are only provisional (not validated) - the original
values are also still available. These new values are nevertheless used for a ‘trial-period’ and
a timer of three minutes duration started. It is now your job to establish a new web server
connection to the device, using the new settings and to click on “Modify / validate settings”. If
you do this the check box names “Settings validated” will be checked, the new parameters
are validated in flash and the old ones deleted. This in the knowledge that the new values
are also really workable ones – how would you otherwise have been able to validate them?
Imagine however that a change really rendered the device unreachable – for example the
LAN speed was really incompatible or you made a mistake with the subnet mask. After three
minutes without validation, the provisional values are deleted from flash and, after a further
automatic reset, the original settings are used again. After a short down period you can then
connect as before the change and perform the modifications again, though correcting the
previous mistake. There is therefore no danger of losing contact with the device, even when
a ‘silly’ mistake is made.
Some notes about MAC addresses
If you are using your own device behind a router and it is not visible to the 'outside world' you can in fact
program any MAC address that you like because it is in a private area. It just has to be unique in this private
area. (This is also valid for a device sitting in a Demiliterized Zone- DMZ)
If however you are selling a product or the device is sitting directly on the Internet then it must have a world
wide unique MAC address which has to be purchased from IEEE. It is purchased either as a block (IAB) of 4k
MAC addresses at a cost of about $500, or if you are going to produce a large number of pieces of equipment
you can purchase a unique company ID (OUI) of 16Million for about $1'600 (plus $2'000 if you don't want the
OUI to be registered on the public listing).
It is then your responsibility to manage the assignment of these addresses in your own products.
The registration page is at: http://standards.ieee.org/regauth/index.html
For any one just wanting to make one or two pieces of equipment for hobby use it is a bit much to pay $500 for
a bunch of MAC addresses and use just one or two of them. Unfortunately it is no allowed to sell the rest on to
people in similar situation because a block must always remain with the individual or organisation purchasing it.
One trick which is often used is to find out what the MAC address is in an old NIC from an old PC which is
being scrapped. This MAC address is then used in your own piece of equipment and the old NIC destroyed.
You can then be sure that the MAC address is unique and can not disturb when used for any imaginable
application.