Modem Test Results

[mchtower]

Hello,

During a pass of the Modem Loopback test the following error occured:

Data compare error: wrote 100, received 218 at index 144

You wouldn't think that more data than was written could be returned, how is that possible? And what does index 144 refer to?

[fwilson]

mchtower,

The 100 and 218 are the values written and read from the registers not the amount of data sent or received.  It wrote 100 but read back 218.  Index 144 is the offset this happend at.

-Fred

[mchtower]

Thanks Fred,

Any idea what might cause that?

[fwilson]

mchtower,

It could be nothing. sometimes memory areas are not writable but the firmware on the system does not report this I have seen systems that accept writes to these kind of areas and just throw them away.

It could also be a bad memory on the card. 
Is the error consistant? Does the modem work?

-Fred

[mchtower]

The error is not consistent. We ran this test 53 times and the error occured only once. We're thinking it was probably some fluky thing but we are trying to get as much detail as possible as to what the error really means and what may have caused it. 

[fwilson]

mchtower,

1 out of 53 times is not a show stopper. Memory is not perfect by any means and modems are well, modems. That is why the ECC and CRC methods are used.

Unless you have a consistant error in a small range of memory (bad memory) or consistant failurs all over the place (Bam memory controller) I wouldn't worry about it.

Transient errors like this can be easily introduced by outside forces als EMI and other forms of radiation can cause problems.

-Fred

[mchtower]

Fred,

Do you have any additional details about what exactly the modem loopback test does? For instance is it using standard modem self test commands such as &T or are you guys doing something different?

[fwilson]

mchtower,

You are correct, it uses standard AT commands.  Nothing fancy and very generic so as to work on as many different modems as possible.

-Fred