[etherlab-users] Bus Scan

Tillman, Scott Scott.Tillman at bhemail.com
Fri Jun 5 23:13:42 CEST 2015

I am only beginning to grok the etherlab stack, but I've got some questions about bus scanning and topology discovery.

First, is there a reason that the user library doesn't have a method to trigger a bus scan?  There is an ioctl for it (EC_IOCTL_MASTER_RESCAN), and the ethercat tool uses that to trigger a rescan, but I don't see any way to reach this from the library (struct ec_master is opaque to the library user, so I can't just call ioctl).

When the bus scan fails (under a VM this happens a lot during SII reading) there doesn't seem to be any direct indication of this.  The best indicator I can find is that the VendorId and ProductCode fields are zeroed out for a slave that failed.  Shouldn't there be a status of some kind?

Since the bus scan takes a significant amount of time, is it possible to request a scan of only the slave(s) that failed?  It doesn't look like it, but I thought maybe I missed something.

When the master is active I understand the very low response timeout (500us).  However, when the master is deactivated we aren't guaranteed to be in real time context, so that's a *really* small timeout.  Isn't it reasonable to have a much longer timeout value for deactivated communications?  On my development VM (using a USB to Ethernet adapter) I have to increase the timeout more than 1000x to avoid timeouts and failures in the bus scan.  More generally, is there a reason that a user shouldn't be able to set the timeouts programmatically, so I can set it via config file based on deployment platform?

I see a wait queue tied to the bus scan completion, but there doesn't appear to be a way to use it to just wait until scan completion.  I'd like to be able to setup a thread that monitored the bus for changes and reacted, but it looks like that requires polling of the scan_busy flag?  At the moment it looks like the only way to reach this wait queue is via ec_master_enter_operation_phase.

When topologies change during active operation is there a way to use the slave port connectivity graph to indicate device configuration information?  I know what my maximal configuration will be, and I know that dynamic connect/disconnect will affect a specific port<->port edge.  That doesn't alter any configuration except devices sharing that edge.  Tying config info to auto-inc addresses seems fragile.  Has this or anything like it be discussed previously?

-Scott Tillman
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