modem: cmux: Handle C/R bit from address field #96617
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| modem_cmux_log_received_frame(&cmux->frame); | ||
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| if (cmux->state == MODEM_CMUX_STATE_CONNECTED && cmux->frame.cr == cmux->initiator) { | ||
| LOG_DBG("Received a response frame, dropping"); |
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Received a response frame? Shouldn't this rather say that the received C/R bit is wrong?
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It is not wrong. See 3GPP TS 27.010: 5.2.1.2 Address Field
The value of the C/R bit changes its meaning depending on which side send the packet.
Most implementations don't care, but for certain commands where the response is exact copy of the command, we should be able to distinct if we just received a response to our command or was this a new command.
In this PR, I'm not doing other than dropping unexpected frames, but on my follow up PR that I'm working, I use this information to know that our Power Saving Command is actually replied and we can shut down the UART.
Same with Close Down command.
| static void modem_cmux_on_dlci_frame_ua(struct modem_cmux_dlci *dlci) | ||
| { | ||
| /* Drop invalid UA frames */ | ||
| if (dlci->cmux->frame.cr != dlci->cmux->initiator) { |
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Shouldn't this rather be
| if (dlci->cmux->frame.cr != dlci->cmux->initiator) { | |
| if (dlci->cmux->frame.cr == dlci->cmux->initiator) { |
as we are receiving the frame?
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See the image on my previous comment.
The value depends on which side of the CMUX pipe we are. So are we initiator or not.
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The C/R bit in the address field should be handled as explained in 5.2.1.2 in the spec (3GPP TS 127.010). To detect if the frame is a command or a response, we need to know who was the initiator of the CMUX channel. > Initiator is the station that take the initiative to initialize > the multiplexer (i.e. sends the SABM command at DLCI 0 ) See the table from given section of the specification. Also, on UIH frames 5.4.3.1 says > The frames sent by the initiating station have the C/R bit set to 1 > and those sent by the responding station have the C/R bit set to 0. NOTE: This is different than a C/R bit in the Type field. Signed-off-by: Seppo Takalo <[email protected]>
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The C/R bit in the address field should be handled as explained in 5.2.1.2 in the spec (3GPP TS 127.010).
To detect if the frame is a command or a response, we need to know who was the initiator of the CMUX channel.
See the table from given section of the specification.
Also, on UIH frames 5.4.3.1 says
NOTE: This is different than a C/R bit in the Type field.