Linux/PROCESSOR-SDK-AM335X: UART2 configuration on Beaglebone Black

sarfaraz shaikh

Tool/software: Linux

I am trying to use UART 2 available on Beaglebone black board. the Pins are 21 and 22 on P9 header. I tried the online Ti Pin Mux utility. The Mux values that I got in TI PIN MUX tools are as follows.

myuart3_pins_default: myuart3_pins_default {
pinctrl-single,pins = <
0x10c ( PIN_INPUT_PULLUP | MUX_MODE6 ) /* (H17) gmii1_crs.uart2_rxd */
0x130 ( PIN_OUTPUT_PULLUP | MUX_MODE1 ) /* (L18) gmii1_rxclk.uart2_txd */
>;
};

But these values does not work with the Uart 2. So I tried different below values in device tree and it works fine.

bb_uart2_pins: pinmux_bb_uart2_pins {
pinctrl-single,pins = <
0x154 0x01 /* spi0_d0.uart2_txd | MODE1 */
0x150 0x21 /* spi0_sclk.uart2_rxd | MODE1 */
>;
};

Can anyone let me know why the values from TI Pin mux tools are not working ?

over 7 years ago

0 Biser Gatchev-XID over 7 years ago

TI__Guru**** 393215 points

Reason is H17 and L18 are used on the MII connection to the Ethernet PHY. They are not routed out to P9.

0 sarfaraz shaikh over 7 years ago in reply to Biser Gatchev-XID

Expert 1536 points

But I am using the H17 and L18 as UART2 in Pin mux tool. I have only enabled UART2 in Pin mux and disabled all other components. Still it gives the above value

The device tree file generated in Pin MUX is as follow

myuart7_pins_default: myuart7_pins_default {
pinctrl-single,pins = <
0x10c ( PIN_INPUT_PULLUP | MUX_MODE6 ) /* (H17) gmii1_crs.uart2_rxd */
0x130 ( PIN_OUTPUT_PULLUP | MUX_MODE1 ) /* (L18) gmii1_rxclk.uart2_txd */
>;
};

/* Optional sleep pin settings. Must manually enter values in the below skeleton. */
myuart7_pins_sleep: myuart7_pins_sleep {
pinctrl-single,pins = <
0x10c ( ) /* (H17) gmii1_crs.uart2_rxd */
0x130 ( ) /* (L18) gmii1_rxclk.uart2_txd */
>;
};

It clearly shows that the H17 and L18 Pins are used in MODE6 and MODE1 which is UART2 go there should not be question of ethernet.

0 Biser Gatchev-XID over 7 years ago in reply to sarfaraz shaikh

TI__Guru**** 393215 points

Yes, UART2 signals are available on these pins, but on the BBB PCB they are routed as MII signals. This has nothing to do with the pinmux tool or device tree, this is PCB design. Look at the BBB schematics.

0 sarfaraz shaikh over 7 years ago in reply to Biser Gatchev-XID

Expert 1536 points

so what will be the value of "pinctrl-single,pins" in devicetree to use UART2 on BBB.

0 Biser Gatchev-XID over 7 years ago in reply to sarfaraz shaikh

TI__Guru**** 393215 points

You need to use pins A17 and B17 in Mode 1, like you wrote in your first post.

0 sarfaraz shaikh over 7 years ago in reply to Biser Gatchev-XID

Expert 1536 points

Thanks Biser this resolved my issue.

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Linux/PROCESSOR-SDK-AM335X: UART2 configuration on Beaglebone Black