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Enabling UART1 on AM18X/DA850/OMAP-L138 running Linux
About this page
This page describes steps to enable and verify the UART1/ttyS1 on AM18x/DA850/OAMP-L138 EVMs running linux.
- Merge below series patches if your kernel is prior to PSP release 03.21.00.04.
- Build kernel by following steps specified in below user guide link.
- As UART1 lines on EVM are not available on DB9 connector, user should have custom card on J30 audio expander slot(ref:EVM figure) to connect UART1 lines to DB9.
Enabling flow control on UART1
- Since AHCLKX and AHCLKR pins of McASP are muxed with CTS and RTS of UART1 respectively, UART1 flowcontrol and audio cannot be enabled simultaneously.
- For enabling UART1 flow control make sure to enable flow control by selecting CONFIG_DAVINCI_UART1_AFE and disable McASP by deselecting CONFIG_SND_DA850_SOC_EVM options from menuconfig as shown below.
Select UART1 flow control
System Type ---> <*> TI DaVinci Implementations ---> <*> DA850/OMAP-L138/AM18x based system <*> Enable UART1 flow control
Device Drivers ---> <*> Sound card support ---> <*> Advanced Linux Sound Architecture ---> <*> ALSA for SoC audio support ---> <*> SoC Audio for the TI DAVINCI chip < > SoC Audio support for DA850/OMAP-L138/AM18xx EVM
- Make sure that AUDIO_EXP_SEL is driven high by turning S7-2(ref:EVM figure) switch ON, otherwise the UART1_CTS signal will have contention with the AIC_MCLK clock signal(i.e. Flow control will be non-functional).
- UART1 can be verified by connecting 2 EVMs back to back on UART1 using custom made connectors as shown in below figure.
- UART1 port of 2 EVMs are connected using single stranded green wires as shown in above figure and connection are made as shown below:
- Connect UART1_RTS of EVM1 to UART1_CTS of EVM2
- Connect UART1_CTS of EVM1 to UART1_RTS of EVM2
- Connect UART1_TX of EVM1 to UART1_RX of EVM2
- Connect UART1_RX of EVM1 to UART1_TX of EVM2
target1$ cat /dev/ttyS1 target2$ echo <enter_text> > /dev/ttyS1
- Should receive entered text on target1. Above steps can be repeated after enabling flow control.
- UART1 can also be verified on single EVM by doing external loopback connection as below:
- Short RTS-CTS lines of UART1.
- Short TX-RX lines of UART1.
- Write to and read from /dev/ttyS1 from an application. The test is passed if you read back what you written.
- Above test can be rerun after enabling flow control.