Problem with UART2 on AM335x

Liem Le

I am using AM335x-SK board and would like to configure pin 5 and 6 on J11 for UART2 (/dev/ttyO2 on Linux). The problem I run into is I can send from AM335x to other board, but could not receive anything. I looped pin 5 and 6, change program to write to /dev/ttyO2 and read back immediately on /dev/ttyO2, but it still does not work. During this loopback test. Checking the omap_mux and it looks ok to me:

root@am335x-evm:/sys/kernel/debug/omap_mux# cat spi0_sclk

name: spi0_sclk.uart2_rxd (0x44e10950/0x950 = 0x0071), b NA, t NA

mode: OMAP_MUX_MODE1 | AM33XX_PIN_INPUT_PULLUP | AM33XX_SLEWCTRL_SLOW

signals: spi0_sclk | uart2_rxd | i2c2_sda | NA | NA | NA | NA | gpio0_2

root@am335x-evm:/sys/kernel/debug/omap_mux# cat spi0_d0

name: spi0_d0.uart2_txd (0x44e10954/0x954 = 0x0059), b NA, t NA

mode: OMAP_MUX_MODE1 | AM33XX_SLEWCTRL_SLOW

signals: spi0_d0 | uart2_txd | i2c2_scl | NA | NA | NA | NA | gpio0_3

I would appreciate if you can give me some help.

Thanks

over 12 years ago

0 Biser Gatchev-XID over 12 years ago

TI__Guru**** 393215 points

Hi Liem,

You mention that you connect J11 to some other board. Did you check the TX/RX signal levels (idle/transmitting)? Do you have GND connected between the two boards?

0 Liem Le over 12 years ago in reply to Biser Gatchev-XID

Prodigy 110 points

Thank you for your response.

Yes, I did connect the GND between two boards. In the case of loopback test which I connect pin 5 and 6 on the AM335x-Starter Kit, I do not need to do this. Checking with scope, I have the correct voltage level. If I do only a write to /dev/ttyO2, I see a burst of signal that looks correct, but if I do a write and immediately following by a read, I got a continuous stream of signal which stop only when I kill the program.

0 Biser Gatchev-XID over 12 years ago in reply to Liem Le

TI__Guru**** 393215 points

Perhaps you should wait after writing for the data to be shifted out and back in the RX buffer, before doing a read?

0 Liem Le over 12 years ago in reply to Biser Gatchev-XID

Prodigy 110 points

I put a sleep(1) in between and still did not solve the problem. I could not explain why I have continuous stream of signal when I do a read following by a write.

0 Liem Le over 12 years ago in reply to Liem Le

Prodigy 110 points

Thank you very much for your help. I found the answer at http://forums.gentoo.org/viewtopic-t-822047-start-0.html

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Problem with UART2 on AM335x