Imx6 3.14.52 ttymxc1 device tree not play ball

[edwardtyrrell]

Hi,

I have a custom imx6 dual-lite board running fsl-release-bsp Jethro Kernel 3.14.52 and am having some ttymxc1 issues.

The first issue is that the device tree set-up refuses to work with our TX and RX pins with respect to the requirements of the external hardware. The hardware requires this:

MX6QDL_PAD_EIM_D26__UART2_TX_DATA

MX6QDL_PAD_EIM_D27__UART2_RX_DATA

No data results in the above configuration (external device removed). No handshaking has been defined.

IF we swap the lines in the device tree, remove the external device to prevent pin contentions, the setup below works but of course the RX and TX are swapped to what our board requires. Swap it back as above - nothing.

MX6QDL_PAD_EIM_D26__UART2_RX_DATA

MX6QDL_PAD_EIM_D27__UART2_TX_DATA

This is tested with no RTS/CTS/DTE..... etc.

Second problem is we actually need to use the RTS/CTS lines for handshaking with a RS485 device. From terminal a simple echo test to /dev/ttymxc1 shows on a scope the RTS spanning the data but strangely the CTS line seems to have no effect whatsoever with the line held in either direction. To add to this, (FYI same uart as above), if the CTS and RTS lines are swapped in the device tree there is no change; RTS still comes out on the same line either way. 

Thanks,

Edward.

[Yuri · Accepted solution]

Hello,

  Perhaps the problem concerns with the fact, that IMX6 UART has some specific

implementation features. The i.MX6 Reference Manuals provides description about

internal signals and (external) multiplexing for them. Table in the Datasheets helps

to clarify it.

Also - the next thread in Community may be helpful :

i.MX6: What does the DTE/DCE in i.MX6's UART do and how are RTS and CTS affected by the UARTxUFCR[DT...

Have a great day,
Yuri

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