p1012: How to detect end of frame in the transparent controller?

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p1012: How to detect end of frame in the transparent controller?

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carlpeng
Contributor II

Hello,

I have some puzzles for transparent controller of p1012 QE, could you please give some suggestions? 

The questions is:  how to detect end of frame in the transparent transfer?

As the QEIWRM.pdf said, user must use the CD line to alert the transparent controller of the end of frame.

but as the below figure show:

we can find that, if CD is negation, will be CD lost, then in the RxBD, the CD flag will be set, controller consider

that a CD lost happened, and the frame will be discarded.

so, my question is how to use CD line to alert the end of frame?

pastedImage_1.png 

Thank you!

Carl

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r8070z
NXP Employee
NXP Employee

Have a great day,

First we should define what is frame in the transparent mode. For example software can test received stream for predefined pattern which is recognized as a frame delimiter. In this case CD lost before the end of frame pattern will abort frame reception and CD lost is considered as error.
The CD lost itself also can be used to signal end of frame. I.e. the CD signal may envelope the frame. In this case negation of CD just terminates frame reception. This is shown on your figure (CD Lost Condition Terminates Reception of Frame). Notice on CD lost the transparent receiver closes Rx buffer and besides CD bit it also sets the last (L) bit and writes the number of frame octets to the data length field.

 

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carlpeng
Contributor II

Hello Serguei,

Thanks a lot for you kind response!

But I still has some puzzles.

As you mentioned, can use CD signal to signal the end of frame, then how to use it? 

Since when controller detects the CD lost condition, it will discard the frame, so we can not 

read the received frame.

Thank you,

Carl

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r8070z
NXP Employee
NXP Employee

"CD Lost Condition Terminates Reception of Frame" means that transparent controller stops to receive. It does not discard frame data it has received before CD lost condition. The received data are in the Rx buffers. And descriptor of the last Rx buffer with frame data is marked by the CD and L bits. After CD Lost the receiver returns to the hunter mode, i.e. it is waiting for the CD signal to start reseption of the next frame. And so on...

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