[RTnet-developers] some suggestions for the next TDMA version

[Karl R. <Kar...@gm...>]

Hello,

I'm currently working on getting RTnet working on an Infineon TriCore 1130 and found some issues, which could be solved in the next major TDMA version comming with RTnet. Would like to discuss these issues to see other's opinion about that.

The TriCore1 architecture is a little bit tricky. When you want to send a frame over Ethernet, the host (the "cpu") has to write it into a shared memory (available via FPI bus). Then the host writes a special register to tell the DMUT (Data Management Unit Transmit) to get this Frame from shared memory and write it into Transmit Buffer TB. The TX block of the MAC takes the frame from TB and sends it to MII, which will put it on the wire. All this can be found in detail in [1], chapter 31.

Here comes the problem: When sending request calibration frames, one has to provide a transmission time stamp as close as possible to the real transmission time. As the TriCore does not support changing the frame after writing it into shared memory (by host), there is no way for providing a real transmission time stamp. Only option is to put the scheduled transmission time there which will have the effect, that transmission time on the wire t_trans is always calculated to long because the real transmission is done later.

To fix this issue there will be a few possibilities, one comes here: One could change TDMA.spec and allow slaves to send a two-parted request calibration frame. First one has a don't care Transmission Time stamp (marked as don't care by a bit or sth similiar). Slaves will notice their transmission time stamp in their TXISR, and send it in the second ReqCalFrm. This would make the whole process much more precise, but of course requires changes in TDMA.spec.


I would really appreciate to get your opinions and comments to that idea!

Karl


[1] http://www.infineon.com/cms/en/services/download.html?filename=%2fdgdl%2ftc1130_um_v1.3_2004_11_per.pdf%3ffolderId%3ddb3a304412b407950112b41b37c12c2b%26fileId%3ddb3a304412b407950112b41b38162c2c&location=Products.Microcontrollers.32-Bit.TC1130_Family__TC1130__TC1115__TC1100_.TC1130.DOCUMENTS.tc1130_um_v1.3_2004_11_per.pdf
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von Karl Reichert

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