How to set up UART2 in J990

	This How-To was tested under Kernel 2.6.35.y but content are valid for Kernel 2.6.37.y

Overview

This How-To is meant to be a starting point for people to learn to set up UART2 for IGEPv2 J990 connector as quickly and easily as possible. In this how-to, we use Linaro Headless with Kernel 2.6.35.y.

More information about UART: here and here.

There are three modes to configure UART2 in J990: via user space (first way), editing only igep.ini (second way) or editing kernel source and compile it (third way).

NOTE: UART2 in j990 connector has CMOS voltages (0V-1V8).

Feedback and Contributing

At any point, if you see a mistake you can contribute to this How-To.

First way

First way: this mode has an issue, when your system reboot or shutdown you will need to configure again. Using user space to configure mux and disable bluetooth.

Configure IGEP

If you use a IGEPv2 Expansion Board, don't use modem for this tutorial

Disable Bluetooth:

Logging with root user via SSH or Serial cable.
NOTE: Poky distribution does not have debug filesystem enabled. Mount it:

mount -t debugfs none /sys/kernel/debug

Go to /sys/kernel/debug/omap_mux/

Set sdmmc2_dat5 to gpio137 (mode 4):

echo 0x004 > sdmmc2_dat5 

Revise that:

root@localhost:/sys/kernel/debug/omap_mux# cat sdmmc2_dat5
name: sdmmc2_dat5.gpio_137 (0x48002166/0x136 = 0x0004), b ah3, t NA
mode: OMAP_PIN_OUTPUT | OMAP_MUX_MODE4
signals: sdmmc2_dat5 | sdmmc2_dir_dat1 | cam_global_reset | sdmmc3_dat1 | gpio_137 | hsusb3_tll_stp | mm3_rxdp | safe_mode

Go to: /sys/class/gpio/

Check that gpio137 is in user space:

root@localhost:/sys/class/gpio# ls
export  gpio137  gpio138  gpio139  gpio170  gpio64  gpiochip0  gpiochip128  gpiochip160  gpiochip192  gpiochip32  gpiochip64  gpiochip96  unexport
root@localhost:/sys/class/gpio# 

If you don't have it, you should export gpio137:

echo 137 > /sys/class/gpio/export 

Set gpio137 to low value to disable bluetooth:

echo 0 > /sys/class/gpio/gpio137/value

Revise that:

root@localhost:/sys/class/gpio# cat /sys/class/gpio/gpio137/value 
0
root@localhost:/sys/class/gpio# 

Disable Bluetooth UART2 wires:

Go to /sys/kernel/debug/omap_mux/

Type:

echo 0x007 > uart2_cts
echo 0x007 > uart2_rts
echo 0x007 > uart2_rx
echo 0x007 > uart2_tx 

Revise that:

root@localhost:/sys/kernel/debug/omap_mux# cat uart2_cts 
name: uart2_cts.safe_mode (0x48002174/0x144 = 0x0007), b ab26, t NA
mode: OMAP_PIN_OUTPUT | OMAP_MUX_MODE7
signals: uart2_cts | mcbsp3_dx | gpt9_pwm_evt | NA | gpio_144 | NA | NA | safe_mode
root@localhost:/sys/kernel/debug/omap_mux# cat uart2_rts 
name: uart2_rts.safe_mode (0x48002176/0x146 = 0x0007), b ab25, t NA
mode: OMAP_PIN_OUTPUT | OMAP_MUX_MODE7
signals: uart2_rts | mcbsp3_dr | gpt10_pwm_evt | NA | gpio_145 | NA | NA | safe_mode
root@localhost:/sys/kernel/debug/omap_mux# cat uart2_rx 
name: uart2_rx.safe_mode (0x4800217a/0x14a = 0x0007), b ad25, t NA
mode: OMAP_PIN_OUTPUT | OMAP_MUX_MODE7
signals: uart2_rx | mcbsp3_fsx | gpt8_pwm_evt | NA | gpio_147 | NA | NA | safe_mode
root@localhost:/sys/kernel/debug/omap_mux# cat uart2_tx
name: uart2_tx.safe_mode (0x48002178/0x148 = 0x0007), b aa25, t NA
mode: OMAP_PIN_OUTPUT | OMAP_MUX_MODE7
signals: uart2_tx | mcbsp3_clkx | gpt11_pwm_evt | NA | gpio_146 | NA | NA | safe_mode
root@localhost:/sys/kernel/debug/omap_mux# 
 

Mode will be 7 (safe_mode)

Enable UART2 in J990:

Type:

echo 0x101 > mcbsp3_dx
echo 0x101 > mcbsp3_clkx
echo 0x101 > mcbsp3_fsx
echo 0x101 > mcbsp3_dr 

Revise that:

root@localhost:/sys/kernel/debug/omap_mux# cat mcbsp3_dx 
name: mcbsp3_dx.uart2_cts (0x4800216c/0x13c = 0x0101), b af6, t NA
mode: OMAP_PIN_INPUT | OMAP_MUX_MODE1
signals: mcbsp3_dx | uart2_cts | NA | NA | gpio_140 | hsusb3_tll_data4 | NA | safe_mode
root@localhost:/sys/kernel/debug/omap_mux# cat mcbsp3_clkx 
name: mcbsp3_clkx.uart2_tx (0x48002170/0x140 = 0x0101), b af5, t NA
mode: OMAP_PIN_INPUT | OMAP_MUX_MODE1
signals: mcbsp3_clkx | uart2_tx | NA | NA | gpio_142 | hsusb3_tll_data6 | NA | safe_mode
root@localhost:/sys/kernel/debug/omap_mux# cat mcbsp3_fsx  
name: mcbsp3_fsx.uart2_rx (0x48002172/0x142 = 0x0101), b ae5, t NA
mode: OMAP_PIN_INPUT | OMAP_MUX_MODE1
signals: mcbsp3_fsx | uart2_rx | NA | NA | gpio_143 | hsusb3_tll_data7 | NA | safe_mode
root@localhost:/sys/kernel/debug/omap_mux# cat mcbsp3_dr 
name: mcbsp3_dr.uart2_rts (0x4800216e/0x13e = 0x0101), b ae6, t NA
mode: OMAP_PIN_INPUT | OMAP_MUX_MODE1
signals: mcbsp3_dr | uart2_rts | NA | NA | gpio_141 | hsusb3_tll_data5 | NA | safe_mode
root@localhost:/sys/kernel/debug/omap_mux# 
 

Mode will be 1 (uart mode)

Second way

Second way: configure kernel via IGEP Xloader. Configuration will be permanent.

NOTE: Only configures UART2_TX(6) and UART2_RX(8). You can not use UART2_CTS(4) AND UART2_RTS(10) which are usually referred to as hardware flow control. For example you can use RS232 but not RS485 peripheral. Don't use minicom with hardware flow control enable.
Go to igep.ini file, replaced by or type this:

buddy=igep0022 
buddy.modem=yes 

Third way

Third way: configure kernel sources. Configuration will be permanent. There are many ways to edit source code, this method is focused for igep0020 RC without igep0022 support.

Configure Kernel source code

Disable TWL4030 PCM voice interface:

Default kernel  has disabled TWL4030 PCM voice interface output pins to high impedance, otherwise this module forces the level of mcbsp3_fsx (uart2_rx) and mcbsp3_clkx (uart2_tx) pins. To make sure, go to $(kernel path)/sound/soc/codecs/twl4030.c file already read:

	0x04, /* REG_VOICE_IF		(0xF)	*/

Disable bluetooth:

Go to $(kernel path)/arch/arm/mach-omap2/board-igep0020.c and search next line:

	else if (hwrev == IGEP2_BOARD_HWREV_C)
		igep00x0_wifi_bt_init(IGEP2_RC_GPIO_WIFI_NPD,
			IGEP2_RC_GPIO_WIFI_NRESET, IGEP2_RC_GPIO_BT_NRESET,
			!opt); 

"igep00x0_wifi_bt_init" function initializes WIFI and Bluetooth peripherals. "opt" variable is used for disable Bluetooth in some cases: enabled (opt!=0) or disabled (opt==0). For example you can disable it permanently replacing "opt" by 1:

	else if (hwrev == IGEP2_BOARD_HWREV_C)
		igep00x0_wifi_bt_init(IGEP2_RC_GPIO_WIFI_NPD,
			IGEP2_RC_GPIO_WIFI_NRESET, IGEP2_RC_GPIO_BT_NRESET,
			!1); 

Disable UART2 default configuration:

Search again at the same file: "static struct omap_board_mux board_mux[] __initdata". Remove the following fields:

	OMAP3_MUX(UART2_TX, OMAP_MUX_MODE0 | OMAP_PIN_OUTPUT),
	OMAP3_MUX(UART2_RX, OMAP_MUX_MODE0 | OMAP_PIN_INPUT), 

Add the following fields below:

	OMAP3_MUX(UART2_TX, OMAP_MUX_MODE7 | OMAP_PIN_INPUT),
	OMAP3_MUX(UART2_RX, OMAP_MUX_MODE7 | OMAP_PIN_INPUT),
	OMAP3_MUX(UART2_RTS, OMAP_MUX_MODE7 | OMAP_PIN_INPUT),
	OMAP3_MUX(UART2_CTS, OMAP_MUX_MODE7 | OMAP_PIN_INPUT), 

Enable UART2 in J990:

Add the following fields under "OMAP3_MUX(UART2_CTS, OMAP_MUX_MODE7 | OMAP_PIN_INPUT), " : 

	OMAP3_MUX(MCBSP3_DR, OMAP_MUX_MODE1 | OMAP_PIN_INPUT),
	OMAP3_MUX(MCBSP3_DX, OMAP_MUX_MODE1 | OMAP_PIN_INPUT),
	OMAP3_MUX(MCBSP3_FSX, OMAP_MUX_MODE1 | OMAP_PIN_INPUT),
	OMAP3_MUX(MCBSP3_CLKX, OMAP_MUX_MODE1 | OMAP_PIN_INPUT),

Compile kernel source code

Use this tutorial (Kernel) and this other (IGEPxloader) to install Linaro Headless with your custom kernel in SD card.  You can compile the IGEPxloader, but is not necessary.
NOTE: for Kernel 2.6.37.y you can use this tutorial removing default kernel for your new one

Test UART2 in J990

UART2 J990 pins:

Pin	UART	Wire
4	UART2_CTS	MCBSP3_DX
6	UART2_TX	MCBSP3_CLKX
8	UART2_RX	MCBSP3_FSX
10	UART2_RTS	MCBSP3_DR

Test

NOTE: Starting from Kernel 2.6.37.y, ttySx are named ttyOx.

Connect UART2_TX with UART2_RX. Use minicom to prove UART2 (/dev/ttyS1) :

minicom -D /dev/ttyS1

or

microcom /dev/ttyS1 

If you write characters and see the echo on the screen, you configure correctly UART.