Mo 68A User Guide¶

Version 1.0 · Beijing InHand Networks Technology Co., Ltd.

Concern	Where to read
Fastest path (flash SD, wiring, first login)	Mo 68A Quick Start Guide
Connector pinouts, electrical and mechanical specs	Mo 68A Hardware Reference Manual
Hostname, timezone, locale, apt after the wizard	§3 Getting Started
Software install and upgrade	§4 Software Management
SD partitioning and free space	§5 Micro SD Card
Serial troubleshooting and early boot log	§6 Debug Serial Console
No display or DisplayPort compatibility	§7 Mini DisplayPort, §19.5 Display No Signal
Ethernet and SSH	§8 Network and Remote Access
Fan required and thermal control	§9 Fan and Thermal Management
Sensors / RTC / EEPROM on I2C	§10 I2C, §11 RTC
USB audio / storage / HID	§12 USB
NVMe / PCIe expansion	§13 PCIe
Raspberry Pi HAT, GPIO / SPI / UART	§14 40-pin GPIO Header
MIPI CSI camera or DSI display	§15 MIPI FPC Ports, §16 MIPI DSI Display, §17 Camera Input
AI inference / MMA	§18 AI Inference Acceleration
Boot failure, network, NVMe, display	§19 Troubleshooting

1. Introduction¶

1.1 Product Overview¶

Mo 68A is a single-board computer built around the TDA4VE / AM68A SoC (TI J721S2 family). It features dual Cortex-A72 application cores, up to six Cortex-R5F MCU cores, and an 8 TOPS AI accelerator, all in a Raspberry Pi 40-pin HAT-compatible form factor.

The board runs Armbian Linux (Debian 13 Trixie) and is suited for AI edge inference, machine vision, embedded Linux development, and industrial computing applications.

1.2 Key Specifications¶

Parameter	Value
SoC	TDA4VE / AM68A (TI J721S2)
CPU	2× ARM Cortex-A72, up to 2.0 GHz
AI Accelerator	8 TOPS (MMA)
RAM	8 GB LPDDR4
Storage	Micro SD (primary); PCIe NVMe (expansion)
OS	Armbian (Debian 13 Trixie)
Networking	Gigabit Ethernet
USB	4× USB 3.0 Type-A
Display	Mini DisplayPort
Camera/Display	2× MIPI 22-pin FPC (CSI-2 / DSI)
Expansion	40-pin GPIO header (RPi HAT compatible)
Power input	USB-C, 5 V / 5 A (27 W)

1.3 Document Scope¶

Document	Covers
Mo 68A Quick Start Guide	Shortest path: flash SD, wiring, power-on, first login, and network access
Mo 68A User Guide (this document)	Interface usage, peripheral configuration, system administration, troubleshooting
Mo 68A Hardware Reference Manual	Circuit and connector definitions, key components, mechanical reference

This guide assumes you have completed SD image flashing and first-time initialization from the Quick Start Guide. If not, read the Shortest path section in the Mo 68A Quick Start Guide first.

2. Accessories and Requirements¶

Item	Specification	Notes
USB-C power adapter	5 V / 5 A (25 W minimum)	Required
Micro SD card	≥ 16 GB, Class 10 / UHS-I	Required
PWM fan (4-pin)	5 V	Required for thermal management
RJ45 Ethernet cable	—	Required
Mini DisplayPort cable	—	Desktop use
DisplayPort monitor	DisplayPort input	Desktop use
USB keyboard and mouse	—	Desktop use
USB-to-UART adapter	3.3 V logic	Serial debug console
RTC battery	CR2032, 2-pin JST-SH	Optional; required for RTC

3. Getting Started¶

3.1 Initial Setup¶

Follow the Mo 68A Quick Start Guide to:

Flash the Armbian image to a Micro SD card
Connect all peripherals (fan, display, Ethernet, power — in that order)
Complete the first-login initialization wizard (locale, timezone, user account)

The board is ready for use when the green LED (D1) is solid.

3.2 Verify System Status¶

After login, confirm the system is running correctly:

# Kernel version
uname -r

# OS information
cat /etc/os-release

# Storage layout
lsblk

# Memory
free -h

# Network
ip addr show eth0

Expected output: root filesystem on /dev/mmcblk1p2, eth0 with an assigned IP address. If an NVMe SSD is installed, /dev/nvme0n1 will also appear in the lsblk output.

3.3 Recommended Initial Configuration¶

Set hostname:

1	`hostnamectl set-hostname Mo68A`

Set timezone (replace with your local timezone):

timedatectl set-timezone Asia/Shanghai
timedatectl status

Update package list:

1	`apt update`

Set locale:

1	`dpkg-reconfigure locales`

4. Software Management¶

Mo 68A runs Armbian Linux (Debian 13 Trixie). Package management uses apt, the standard Debian package manager. All commands below should be run as root or with sudo.

Update package index (run before installing or upgrading):

1	`apt update`

Install a package:

1	`apt install <package>`

Remove a package:

# Keep configuration files
apt remove <package>

# Remove package and its configuration files
apt purge <package>

Remove unused dependencies:

1	`apt autoremove`

Upgrade all installed packages:

1	`apt upgrade`

Search for packages by keyword:

1	`apt search <keyword>`

Show package details:

1	`apt show <package>`

5. Micro SD Card¶

The Micro SD card is the primary boot medium and root filesystem storage. It contains two partitions:

Partition	Size	Mount point	Purpose
`mmcblk1p1`	256 MB	`/boot`	Kernel, device tree, overlays
`mmcblk1p2`	Remaining	`/`	Root filesystem

View partition layout:

1	`lsblk /dev/mmcblk1`

Example output:

NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
mmcblk1     179:0    0 29.7G  0 disk
├─mmcblk1p1 179:1    0  256M  0 part /boot
└─mmcblk1p2 179:2    0 29.2G  0 part /var/log.hdd
                                     /

mmcblk1p2 shows two mount points: / (root filesystem) and /var/log.hdd. Armbian mounts /var/log as a tmpfs at runtime to reduce SD card wear; /var/log.hdd is the persistent log directory on the SD card.

Check available space:

df -h /

On first boot, Armbian automatically expands the root partition to fill the SD card. This triggers one automatic reboot and takes 1–2 minutes.

6. Debug Serial Console¶

The board provides a hardware serial console on connector J6 (SH1.0 3-pin). This console outputs the full boot log and provides a login prompt independent of the display or network — making it essential for headless setup, kernel debugging, and recovery.

6.1 Hardware Connection¶

Connect a 3.3 V USB-to-UART adapter to J6:

Pin	Signal
1	RXD
2	GND
3	TXD

Warning: Use a 3.3 V logic adapter only. A 5 V adapter will damage the board.

Connect the adapter before applying power to capture the full boot log from the start.

6.2 Terminal Setup¶

Settings: 115200 baud, 8N1, no flow control

# Linux
minicom -D /dev/ttyUSB0 -b 115200

On Windows, use PuTTY or Tera Term and select the correct COM port.

The console device on the board is /dev/ttyS2 (UART8). This port is dedicated to the debug console — do not use it for general-purpose UART communication.

7. Mini DisplayPort¶

Connect a DisplayPort monitor to J9 (Mini DisplayPort). The board outputs video after the desktop environment loads.

The display must have a native DisplayPort input. A passive Mini DP to HDMI adapter will not work; use an active adapter or a DP-native monitor.

Check display detection:

1	`cat /sys/class/drm/card/card-DP-*/status`

8. Network and Remote Access¶

8.1 Wired Ethernet¶

The board uses NetworkManager. The Ethernet interface is eth0 and uses DHCP by default.

Check connection status:

1	`nmcli device status`

View assigned IP address:

ip addr show eth0

Configure a static IP address:

nmcli con mod "Wired connection 1" \
  ipv4.method manual \
  ipv4.addresses 192.168.1.100/24 \
  ipv4.gateway 192.168.1.1 \
  ipv4.dns "8.8.8.8 8.8.4.4"
nmcli con up "Wired connection 1"

Revert to DHCP:

nmcli con mod "Wired connection 1" ipv4.method auto
nmcli con up "Wired connection 1"

8.2 SSH Access¶

SSH server is enabled by default. Connect from a host computer:

1	`ssh <username>@<board-ip>`

9. Fan and Thermal Management¶

9.1 Fan Connector¶

Connect a 5 V 4-pin PWM fan to J7 (SH1.0, 1.0 mm pitch):

Pin	Signal	Direction
1	5 V	Power out
2	PWM	Output to fan
3	GND	Ground
4	TACH	Input from fan

9.2 Automatic Speed Control¶

Fan speed is controlled automatically by the kernel thermal governor based on the SoC temperature. The fan always runs at a minimum of 20% speed; it ramps up as temperature rises.

Temperature (main0-thermal)	Fan speed
Below 60 °C	20 %
60 – 70 °C	40 – 60 %
70 – 80 °C	60 – 80 %
Above 80 °C	80 – 100 %

The PWM signal runs at 25 kHz. Speed transitions are stepped by the governor on each 1-second polling cycle.

9.3 Monitoring¶

Fan speed (RPM):

1	`cat /sys/class/hwmon/hwmon0/fan1_input`

Example output:

RPM is measured from the TACH signal: the driver counts falling edges on the tachometer input and samples once per second. Accuracy depends on the fan's pulses-per-revolution specification (2 pulses/rev assumed, standard for most 4-pin PWM fans).

PWM output state:

1	`cat /sys/kernel/debug/pwm`

Example output (idle, 20 % duty cycle):

1
2
3

0: platform/3010000.pwm, 2 PWM devices
 pwm-0   ((null)   ): period: 0 ns duty: 0 ns polarity: normal
 pwm-1   (pwm-fan  ): requested enabled period: 40000 ns duty: 8000 ns polarity: normal usage_power

The duty value divided by period gives the current duty cycle (8000 / 40000 = 20 %).

Current cooling level:

cat /sys/class/thermal/cooling_device0/cur_state   # 0–4
cat /sys/class/thermal/cooling_device0/max_state   # 4

All zone temperatures:

for z in /sys/class/thermal/thermal_zone*/; do
  printf '%-20s %d °C\n' "$(cat ${z}type)" "$(($(cat ${z}temp) / 1000))"
done

Example output:

wkup0-thermal        50 °C
wkup1-thermal        50 °C
main0-thermal        50 °C
main1-thermal        51 °C
main2-thermal        51 °C
main3-thermal        51 °C
main4-thermal        50 °C

The fan is controlled by main0-thermal (thermal_zone2). To monitor it continuously:

watch -n 2 cat /sys/class/thermal/thermal_zone2/temp

10. I2C¶

The SoC exposes five I2C buses. Use i2cdetect -l to list them:

1	`i2cdetect -l`

Example output:

i2c-0   i2c             OMAP I2C adapter                        I2C adapter
i2c-1   i2c             OMAP I2C adapter                        I2C adapter
i2c-2   i2c             OMAP I2C adapter                        I2C adapter
i2c-3   i2c             OMAP I2C adapter                        I2C adapter
i2c-4   i2c             a000000.dp-bridge                       I2C adapter

Device node	SoC bus	Connected to	40-pin pins
`/dev/i2c-0`	WKUP I2C0	PMIC and power ICs	27, 28 (shared with PMIC — use with care)
`/dev/i2c-1`	SOC I2C0	40-pin header (user)	3, 5
`/dev/i2c-2`	SOC I2C1	Board EEPROM (0x50), RTC (0x51)	—
`/dev/i2c-3`	SOC I2C5	MIPI FPC (internal)	—
`/dev/i2c-4`	DP AUX	Mini DisplayPort (AUX channel)	—

Caution: /dev/i2c-0 (pins 27, 28) is shared with the PMIC. Incorrect transactions on this bus can affect system power rails. Scan or access it only if you understand the consequences.

Caution: /dev/i2c-4 is the DisplayPort AUX channel I2C adapter, used internally by the display subsystem. Do not scan or access this bus.

Scan an I2C bus:

i2cdetect -y -r <bus>

The -r flag uses read-mode probing, which is safer than the default Quick Write mode.

Example — scan the 40-pin user I2C bus (SOC I2C0, pins 3 and 5):

i2cdetect -y -r 1

Read a register:

i2cget -y <bus> <addr> <reg>

Dump all registers of a device:

i2cdump -y <bus> <addr>

Write a register:

i2cset -y <bus> <addr> <reg> <value>

Warning: i2cset writes directly to device registers and takes effect immediately. Writing incorrect values to the wrong device — especially on bus 0 (PMIC) — can cause system instability or hardware damage. Only use i2cset on known devices with a register map you understand.

11. RTC¶

11.1 Battery Installation¶

The RTC (PCF85263ATL) is backed by a CR2032 battery connected via J8 (SH1.0, 2-pin, 1.0 mm pitch). Install the battery before setting the time to preserve the clock across power cycles.

Use a CR2032 coin cell with a pre-fitted 2-pin JST-SH (1.0 mm pitch) connector. Do not insert a bare coin cell; the JST connector is required.

11.2 Time Configuration¶

Armbian uses systemd-timesyncd to synchronize the system clock from NTP. When network is available, the system time is kept accurate automatically. systemd also writes the system time to the RTC periodically and on shutdown, so the RTC stays in sync without manual intervention.

Verify the RTC driver is loaded:

1	`ls /dev/rtc*`

Check the current time and RTC status:

1	`timedatectl status`

The output includes both Local time (system clock) and RTC time (hardware clock).

To verify the RTC works correctly, disable NTP, set a known time manually, then reboot and confirm the time is preserved.

Disable automatic time synchronization:

timedatectl set-ntp false

Set the system time manually:

timedatectl set-time "2026-05-08 12:00:00"

systemd automatically writes the new time to the RTC. Verify both clocks are updated:

1	`timedatectl status`

Reboot, then confirm the time is preserved:

1
2
3

reboot
# After reboot:
timedatectl status

12. USB¶

The four USB 3.0 Type-A ports provide peripheral expansion. Common scenarios covered in this section include keyboard and mouse input, audio output, and portable storage.

12.1 USB 3.0 Type-A Ports¶

Four USB 3.0 ports are provided via the TUSB8041 hub: two on J2 and two on J3.

List all connected USB devices:

lsusb

Example output with a mouse and keyboard connected:

Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 0451:8142 Texas Instruments, Inc. TUSB8041 4-Port Hub
Bus 001 Device 003: ID 046d:c077 Logitech, Inc. Mouse
Bus 001 Device 004: ID 046d:c31d Logitech, Inc. Media Keyboard K200
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub

The TUSB8041 hub always appears on Bus 001. Devices connected to the Type-A ports appear as additional entries under Bus 001 or Bus 002.

12.2 Keyboard and Mouse¶

USB keyboards and mice are supported out of the box via the USB HID driver. Connect to any Type-A port (J2 or J3) and the device is immediately available — no configuration required.

On the desktop, input is handled by the graphical environment. In headless mode, a USB keyboard is available on a local terminal session.

12.3 USB Audio¶

USB audio devices (speakers, headsets, USB sound cards) are plug-and-play. The kernel's built-in USB Audio Class (UAC) driver requires no configuration — connect the device and it is immediately available as an ALSA sound card.

Step 1 — Verify detection:

lsusb

Example output (USB speaker appears as a new entry under Bus 001):

Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 0451:8142 Texas Instruments, Inc. TUSB8041 4-Port Hub
Bus 001 Device 003: ID 046d:c077 Logitech, Inc. Mouse
Bus 001 Device 004: ID 046d:c31d Logitech, Inc. Media Keyboard K200
Bus 001 Device 008: ID 4c4a:4155 Jieli Technology UACDemoV1.0
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub

Confirm ALSA has registered it as a sound card and find the card number:

1	`aplay -l`

Example output when an I2S audio HAT is also installed (WM8960 takes card 0; USB audio is assigned card 1):

card 0: WM8960Audio [WM8960-Audio], device 0: davinci-mcasp.0-wm8960-hifi wm8960-hifi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: UACDemoV10 [UACDemoV1.0], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Card numbers are assigned in probe order. I2S devices probe before USB, so a USB audio device is card 0 only when no I2S sound card is present.

To find the USB audio card number directly:

aplay -l | grep -i "USB Audio"

Example output:

1	`card 1: UACDemoV10 [UACDemoV1.0], device 0: USB Audio [USB Audio]`

The card number and device number both appear in the output (e.g. card 1:, device 0:). Use those values in all subsequent commands (shown as <C> and <D> below).

Step 2 — Adjust volume:

Query mixer controls and volume range (values are device-specific):

amixer -c <C> contents

Example output for a USB speaker:

numid=2,iface=MIXER,name='PCM Playback Switch'
  ; type=BOOLEAN,access=rw------,values=1
  : values=on

numid=3,iface=MIXER,name='PCM Playback Volume'
  ; type=INTEGER,access=rw---R--,values=2,min=0,max=147,step=0
  : values=44,44
  | dBminmax-min=-28.37dB,max=-0.94dB

Set playback volume (control name and value range vary by device; check amixer contents output):

amixer -c <C> cset name='PCM Playback Volume' 60,60

Mute / unmute:

# Mute
amixer -c <C> cset name='PCM Playback Switch' off

# Unmute
amixer -c <C> cset name='PCM Playback Switch' on

Step 3 — Test playback:

Sine-wave test tone (clearly audible on any speaker):

speaker-test -c 2 -t sine -f 1000 -l 3 -D plughw:<C>,<D>

Play an audio file (plughw handles sample rate and channel conversion automatically):

aplay -D plughw:<C>,<D> audio.wav

USB audio requires no device tree changes and works immediately. The 40-pin I2S interface (§14.5) is an alternative for designs that require an on-board codec.

12.4 USB Drive¶

USB storage is mounted automatically by the desktop environment. In headless mode:

# List block devices
lsblk

# Mount USB storage
mkdir -p /mnt/usb
mount /dev/sda1 /mnt/usb

# Unmount safely before removal
umount /mnt/usb

13. PCIe¶

The PCIe Gen3 FPC connector (J10) provides a high-speed expansion interface for attaching devices such as NVMe SSDs, compute accelerators, or custom PCIe peripherals via an adapter board.

Verified compatible device: KIOXIA KEG60ZNS1T02.

After connecting and booting, verify detection:

1 2	`lsblk ls /dev/nvme*`

Mount an existing partition:

mkdir -p /mnt/nvme
mount /dev/nvme0n1p1 /mnt/nvme

Mount automatically on boot — add to /etc/fstab:

1	`/dev/nvme0n1p1 /mnt/nvme ext4 defaults 0 2`

14. 40-pin GPIO Header¶

The 40-pin header (J11) follows the Raspberry Pi HAT mechanical footprint and pin numbering. For full signal assignments and ball numbers, see HRM §40-pin GPIO header (J11).

IO voltage is 3.3 V. Do not connect 5 V signals to any GPIO pin.

14.1 Pin Reference¶

Function (odd pin)	Pin	Pin	Function (even pin)
3.3 V	1	2	5.0 V
I2C0_SDA (AE24)	3	4	5.0 V
I2C0_SCL (AH25)	5	6	GND
AUDIO_CLK / GPIO0_30 (Y25)	7	8	UART5_TXD (W25)
GND	9	10	UART5_RXD (AC24)
WKUP_GPIO0_60 (E27) †	11	12	I2S_CLK (AB28)
GPIO0_0 (AG24)	13	14	GND
WKUP_GPIO0_61 (E28) †	15	16	GPIO0_27 (V26)
3.3 V	17	18	GPIO0_51 (AE27)
SPI5_MOSI (R27)	19	20	GND
SPI5_MISO (AD27)	21	22	WKUP_GPIO0_70 (B26) †
SPI5_CLK (T27)	23	24	SPI5_CS0 (U28)
GND	25	26	SPI5_CS1 (W28)
WKUP_I2C0_SDA (H27) †	27	28	WKUP_I2C0_SCL (H24) †
GPIO0_18 (AB27)	29	30	GND
GPIO0_33 (AA28)	31	32	PWM / ECAP0 (AB26)
PWM5_B / GPIO0_32 (U26)	33	34	GND
I2S_FS (U27)	35	36	GPIO0_10 (AB24)
GPIO0_9 (Y28)	37	38	I2S_DIN (AC28)
GND	39	40	I2S_DOUT (Y26)

† WKUP-domain GPIO (gpiochip0); all others are main-domain GPIO (gpiochip1).

For I2C commands and bus assignment, see §10. I2C pins on the 40-pin header: pins 3 and 5 (SOC I2C0, /dev/i2c-1), pins 27 and 28 (WKUP I2C0, /dev/i2c-0).

14.2 GPIO¶

Multiple GPIO lines are available on the 40-pin header. The board uses the Linux GPIO character device interface. Tools from the gpiod package (gpiodetect, gpioinfo, gpioget, gpioset) are pre-installed.

List GPIO chips:

1	`gpiodetect`

gpiochip0 [42110000.gpio] (89 lines)   # WKUP domain GPIO (WKUP_GPIO0_X)
gpiochip1 [600000.gpio]   (66 lines)   # Main domain GPIO0 (GPIO0_X)
gpiochip2 [0-0048]        (11 lines)   # Internal system controller (not for user access)
gpiochip3 [7inch-touchscreen-p] (2 lines)   # RPi 7-inch panel (present when panel is connected)

List lines of a GPIO chip (example: gpiochip2):

1	`gpioinfo -c gpiochip2`

gpiochip2 - 11 lines:
        line   0:       unnamed                 input
        line   1:       unnamed                 input
        line   2:       unnamed                 input
        line   3:       unnamed                 input
        line   4:       unnamed                 output
        line   5:       unnamed                 output
        line   6:       unnamed                 input
        line   7:       unnamed                 input
        line   8:       unnamed                 output
        line   9:       unnamed                 input
        line  10:       unnamed                 output

Read a GPIO input (example: GPIO0_0, pin 13):

gpioget -c gpiochip1 0

Output: "0"=active (active = high, inactive = low)

Set a GPIO output (example: GPIO0_0 high, then low):

gpioset -c gpiochip1 0=1
gpioset -c gpiochip1 0=0

Note: gpioset blocks until the process is terminated — the GPIO line is held in the set state until you press Ctrl+C, after which it is released. Only operate lines exposed on the 40-pin header.

Note: Some pins have a non-GPIO default pinmux (for example, pin 7 defaults to AUDIO_CLK). If gpioset has no effect, the pin requires a device tree overlay to switch its pinmux to GPIO mode.

Read a WKUP-domain GPIO (example: WKUP_GPIO0_60, pin 11):

gpioget -c gpiochip0 60

40-pin GPIO line mapping:

Header Pin	Signal	Chip	Line
7	GPIO0_30	gpiochip1	30
11	WKUP_GPIO0_60	gpiochip0	60
13	GPIO0_0	gpiochip1	0
15	WKUP_GPIO0_61	gpiochip0	61
16	GPIO0_27	gpiochip1	27
18	GPIO0_51	gpiochip1	51
22	WKUP_GPIO0_70	gpiochip0	70
29	GPIO0_18	gpiochip1	18
31	GPIO0_33	gpiochip1	33
33	GPIO0_32	gpiochip1	32
36	GPIO0_10	gpiochip1	10
37	GPIO0_9	gpiochip1	9

14.3 SPI¶

SPI5 is available on the 40-pin header and enabled by default. The bus can be used in two ways:

Userspace access via spidev: No overlay required. /dev/spidev1.0 (CS0) is available immediately after boot. Sensors, ADCs, and other peripherals can be driven from userspace using standard SPI libraries (e.g., Python spidev).
Kernel-driver peripherals (e.g., SPI displays): A device tree overlay is required to register the peripheral — specifying its compatible string, chip-select, and maximum clock frequency — so the kernel can bind the appropriate driver.

Pin	Signal	SoC Ball
19	SPI5_MOSI	R27
21	SPI5_MISO	AD27
23	SPI5_CLK	T27
24	SPI5_CS0	U28
26	SPI5_CS1	W28

The device node is /dev/spidev1.0 (CS0).

Verify SPI device node:

1	`ls /dev/spidev*`

Check SPI configuration:

spi-config -d /dev/spidev1.0 -q

Loopback test (connect pin 19 to pin 21 with a jumper wire):

echo -ne '\x55\xAA\x12\x34' | spi-pipe -d /dev/spidev1.0 -s 1000000 | xxd

Expected output:

1	`00000000: 55aa 1234 U..4`

14.4 UART¶

UART5 is available on the 40-pin header, exposed as /dev/ttyS0, and enabled by default.

Pin	Signal	SoC Ball	Direction
8	UART5_TXD	W25	Output
10	UART5_RXD	AC24	Input

The serial debug console (J6, UART8) uses /dev/ttyS2. Do not use /dev/ttyS2 for general-purpose UART communication.

Identifying which ttyS is which:

1 2	`# Show MMIO address for each ttyS — match against SoC datasheet or DTS reg values cat /proc/tty/driver/serial`

The console device can also be identified by its file permissions — it is owned by group tty rather than dialout:

1 2	`crw------- root tty ttyS2 ← debug console (J6), for system administration crw-rw---- root dialout ttyS0 ← general-purpose UART (40-pin header)`

Loopback test:

Short pin 8 (TXD) to pin 10 (RXD) on the 40-pin header, then:

# Configure port: 115200 baud, raw mode, no local echo
stty -F /dev/ttyS0 115200 raw -echo

# Start receiver in background
cat /dev/ttyS0 &

# Send test string — should be echoed back immediately
echo "loopback" > /dev/ttyS0

# Stop receiver: bring to foreground then press Ctrl+C
fg

14.5 I2S / Audio¶

The I2S interface (MCASP0) is available on the 40-pin header. Audio devices are managed through ALSA.

Pin	Signal	SoC Ball	Direction
12	BCLK (MCASP0_ACLKX)	AB28	Output (clock master)
35	LRCLK (MCASP0_AFSX)	U27	Output (clock master)
38	DIN (MCASP0_AXR0)	AC28	Input
40	DOUT (MCASP0_AXR1)	Y26	Output

Using I2S requires an external I2S audio codec IC wired to the 40-pin header and a device tree overlay that registers the codec and MCASP0 as an ALSA sound card. Without the overlay, aplay -l returns "no soundcards found".

The WM8960 Audio HAT is a supported I2S codec HAT that connects to the 40-pin header. The procedure below applies to that HAT. The clock source is the internal MCASP auxiliary clock (196.608 MHz), which divides exactly to 48 kHz family rates; 44.1 kHz playback is possible but runs approximately 4860 PPM off-rate.

Step 1 — Load the overlay:

Edit /boot/uEnv.txt and add (or uncomment) the following line (comment out any other name_overlays lines):

1	`name_overlays=ti/k3-j721s2-panda-wm8960-audio-hat.dtbo`

To combine with a camera overlay, list them space-separated on a single line, e.g.:

1	`name_overlays=ti/k3-j721s2-panda-wm8960-audio-hat.dtbo ti/k3-j721s2-panda-csi2-imx219-mipi0.dtbo`

Reboot after editing.

Step 2 — Verify the sound card is registered:

1	`aplay -l`

Expected output:

1
2
3

card 0: WM8960Audio [WM8960-Audio], device 0: davinci-mcasp.0-wm8960-hifi wm8960-hifi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0

The card number and device number both appear in the output (e.g. card 0:, device 0:). Use those values in all subsequent commands (shown as <C> and <D> below).

Query available mixer controls:

amixer -c <C> scontrols

Step 3 — Initialize mixer controls (the default state may produce no output):

amixer -c <C> sset 'Left Output Mixer PCM' on
amixer -c <C> sset 'Right Output Mixer PCM' on
amixer -c <C> sset Headphone 80%
amixer -c <C> sset Speaker 80%
amixer -c <C> sset Playback 80%

Step 4 — Test playback:

All playback commands use plughw:<C>,<D>, which enables the ALSA plug layer to handle sample-rate conversion, channel mapping, and format adaptation automatically — any audio file can be played regardless of its original sample rate.

Sine-wave test (both channels, 3 loops):

speaker-test -c 2 -t sine -f 1000 -l 3 -D plughw:<C>,<D>

Play an audio file:

aplay -D plughw:<C>,<D> audio.wav

Note: If a USB audio device is also connected it will appear as a separate card. The WM8960 HAT is always card 0 when the overlay is loaded; verify with aplay -l if unsure.

Tip: For most use cases, a USB audio device (§12.3) is simpler — plug-and-play with no hardware wiring or device tree changes required.

Step 5 — Test capture (recording):

The following procedure uses the WM8960 Audio HAT as an example. Control names and gain ranges are specific to this device; other I2S codecs may differ.

Step 5.1 — Confirm the capture device is available:

Lists all hardware devices that support capture. If the list is empty, the sound card has not registered a capture interface.

1	`arecord -l`

Example output:

**** List of CAPTURE Hardware Devices ****
card 0: WM8960Audio [WM8960-Audio], device 0: davinci-mcasp.0-wm8960-hifi wm8960-hifi-0 [davinci-mcasp.0-wm8960-hifi wm8960-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Step 5.2 — Query current capture configuration:

Query the PGA (Programmable Gain Amplifier) gain and mute state. Confirm the output shows [on] (not muted) and gain is non-zero.

amixer -c <C> sget 'Capture'

Example output:

Simple mixer control 'Capture',0
  Capabilities: cvolume cswitch
  Capture channels: Front Left - Front Right
  Limits: Capture 0 - 63
  Front Left: Capture 46 [73%] [17.25dB] [on]
  Front Right: Capture 46 [73%] [17.25dB] [on]

Query whether the Boost amplifier output is connected to the PGA. Confirm both show [on] (Boost path open).

amixer -c <C> sget 'Left Input Mixer Boost'
amixer -c <C> sget 'Right Input Mixer Boost'

Example output:

Simple mixer control 'Left Input Mixer Boost',0
  Capabilities: pswitch pswitch-joined
  Playback channels: Mono
  Mono: Playback [on]

Query the current Boost gain value and its available range. Note the Limits line in the output for use in Step 5.3.

amixer -c <C> sget 'Left Input Boost Mixer LINPUT1'
amixer -c <C> sget 'Right Input Boost Mixer RINPUT1'

Example output:

Simple mixer control 'Left Input Boost Mixer LINPUT1',0
  Capabilities: volume volume-joined
  Playback channels: Mono
  Capture channels: Mono
  Limits: 0 - 3
  Mono: 1 [33%] [13.00dB]

Step 5.3 — Set capture configuration:

If Step 5.2 shows values that differ from the recommended settings, apply the following commands.

Open the Boost amplifier output path to the PGA, allowing the microphone signal to reach the ADC:

amixer -c <C> sset 'Left Input Mixer Boost' on
amixer -c <C> sset 'Right Input Mixer Boost' on

Set the Boost gain (range from Step 5.2: 0–3, corresponding to 0 / +13 / +20 / +29 dB). Recommended starting value: 1 (+13 dB):

amixer -c <C> sset 'Left Input Boost Mixer LINPUT1' 1
amixer -c <C> sset 'Right Input Boost Mixer RINPUT1' 1

Set the PGA gain for left and right channels (range from Step 5.2: 0–63, corresponding to −17 dB to +30 dB). Recommended starting value: 46 (+17 dB):

amixer -c <C> sset 'Capture' 46,46

Total capture gain: Boost +13 dB + PGA +17 dB = +30 dB. If the recording sounds distorted, reduce the gain; if it is too quiet, increase it.

Step 5.4 — Query hardware-supported capture parameters:

Query the formats, sample rates, and channel counts supported by the hardware. Use these values to select parameters for the recording command in Step 5.5.

arecord -D hw:<C>,<D> --dump-hw-params -d 1 /dev/null

Example output:

1
2
3

FORMAT:   S16_LE S32_LE
CHANNELS: [1 2]
RATE:     [8000 48000]

Step 5.5 — Record:

Record audio using parameters derived from Step 5.4:

arecord -D hw:<C>,<D> -f S16_LE -r 48000 -c 2 -d 10 rec.wav

Parameter	Value	Source
`-D hw:<C>,<D>`	Direct hardware access	Card and device numbers from Step 5.1
`-f S16_LE`	16-bit signed little-endian	Step 5.4: FORMAT S16_LE S32_LE
`-r 48000`	48 kHz	Step 5.4: RATE [8000 48000]; 48 kHz divides exactly from the 196.608 MHz MCASP clock
`-c 2`	Stereo	Step 5.4: CHANNELS [1 2]
`-d 10`	10 seconds	Test duration; adjust as needed

Step 5.6 — Verify by playback:

Play back the recording using the ALSA plug layer (plughw), which handles format and sample-rate conversion automatically. If the recorded content is audible, capture is working correctly.

aplay -D plughw:<C>,<D> rec.wav

14.6 PWM¶

Two PWM outputs are available on the 40-pin header:

Pin	Signal	Driver	Device address	Channel
32	ECAP0_IN_APWM_OUT (AB26)	`pwm-tiecap` (ECAP0)	`3100000.pwm`	0
33	PWM5_B / GPIO0_32 (U26)	`pwm-ehrpwm` (EHRPWM5_B)	`3050000.pwm`	1

pwmchip numbers are assigned dynamically at boot and may differ between boards. Always look up the chip by device address before use. 3010000.pwm (EHRPWM1) is reserved for fan speed control.

Show all pwmchip-to-device mappings:

for c in /sys/class/pwm/pwmchip*; do echo "$c -> $(readlink -f $c/device)"; done

Look up the chip number for a specific output:

# ECAP0 (pin 32)
grep -rl 3100000 /sys/class/pwm/pwmchip*/device/uevent | grep -o 'pwmchip[0-9]*'

# EHRPWM5 (pin 33)
grep -rl 3050000 /sys/class/pwm/pwmchip*/device/uevent | grep -o 'pwmchip[0-9]*'

Pin 32 — ECAP0 APWM output¶

Pin 32 uses the SoC's Enhanced Capture (ECAP) module in Asymmetric PWM (APWM) output mode, channel 0:

# Look up chip number
CHIP=$(grep -rl 3100000 /sys/class/pwm/pwmchip*/device/uevent | grep -o 'pwmchip[0-9]*')

# Register channel 0 — creates the pwm0/ control directory
echo 0 > /sys/class/pwm/$CHIP/export

# Set period in nanoseconds (1 000 000 ns = 1 kHz)
echo 1000000 > /sys/class/pwm/$CHIP/pwm0/period

# Set duty cycle in nanoseconds (500 000 ns = 50%)
echo 500000 > /sys/class/pwm/$CHIP/pwm0/duty_cycle

# Start output
echo 1 > /sys/class/pwm/$CHIP/pwm0/enable

To stop the output:

CHIP=$(grep -rl 3100000 /sys/class/pwm/pwmchip*/device/uevent | grep -o 'pwmchip[0-9]*')

# Stop output
echo 0 > /sys/class/pwm/$CHIP/pwm0/enable

# Release channel 0 — removes the pwm0/ directory
echo 0 > /sys/class/pwm/$CHIP/unexport

Pin 33 — EHRPWM5_B output¶

Pin 33 uses EHRPWM5 channel B, channel 1:

# Look up chip number
CHIP=$(grep -rl 3050000 /sys/class/pwm/pwmchip*/device/uevent | grep -o 'pwmchip[0-9]*')

# Register channel 1 (B) — creates the pwm1/ control directory
echo 1 > /sys/class/pwm/$CHIP/export

# Set period in nanoseconds (1 000 000 ns = 1 kHz)
echo 1000000 > /sys/class/pwm/$CHIP/pwm1/period

# Set duty cycle in nanoseconds (500 000 ns = 50%)
echo 500000 > /sys/class/pwm/$CHIP/pwm1/duty_cycle

# Start output
echo 1 > /sys/class/pwm/$CHIP/pwm1/enable

To stop the output:

CHIP=$(grep -rl 3050000 /sys/class/pwm/pwmchip*/device/uevent | grep -o 'pwmchip[0-9]*')

# Stop output
echo 0 > /sys/class/pwm/$CHIP/pwm1/enable

# Release channel 1 (B) — removes the pwm1/ directory
echo 1 > /sys/class/pwm/$CHIP/unexport

15. MIPI FPC Ports¶

15.1 Overview¶

J24 (MIPI0) and J25 (MIPI1) are 22-pin FPC connectors with a MIPI D-PHY interface. Each port can be configured as either CSI-2 camera input or DSI display output via device tree overlay — but not both simultaneously on the same port.

Verified compatible devices:

Camera: Sony IMX219 (e.g., Raspberry Pi Camera Module 2)
Display: Raspberry Pi 7-inch DSI panel (J24 only; see §16)

15.2 Configuration¶

Mode selection is controlled by the name_overlays line in /boot/uEnv.txt. Three scenarios are supported:

Scenario	J24 (MIPI0)	J25 (MIPI1)	`name_overlays`
A	CSI camera	—	`ti/k3-j721s2-panda-csi2-imx219-mipi0.dtbo`
B	—	CSI camera	`ti/k3-j721s2-panda-csi2-imx219-mipi1.dtbo`
C	DSI display	CSI camera	`ti/k3-j721s2-panda-dsi-rpi-7inch-panel.dtbo ti/k3-j721s2-panda-csi2-imx219-mipi1.dtbo`

name_overlays rules:

Each value is a path to a .dtbo file relative to /boot/dtb/
Only the last uncommented name_overlays line takes effect — comment out all others
To load multiple overlays, list them space-separated on a single name_overlays line, e.g. Scenario C:

1	`name_overlays=ti/k3-j721s2-panda-dsi-rpi-7inch-panel.dtbo ti/k3-j721s2-panda-csi2-imx219-mipi1.dtbo`

16. MIPI DSI Display¶

J24 (MIPI0) supports DSI display output. For overlay configuration see §15.2; for combined DSI + camera use see §17.3 (Scenario C).

J25 (MIPI1) DSI support is not currently available.

Warning: The DSI panel must be physically connected to J24 before boot. If the panel is absent, the DSS display subsystem fails to initialize and Mini DisplayPort (J9) will also be unavailable.

17. Camera Input¶

For port hardware overview and overlay configuration rules, see §15.

17.1 Scenario A — J24 Camera¶

Edit /boot/uEnv.txt and uncomment the following line (comment out any other name_overlays lines):

1	`name_overlays=ti/k3-j721s2-panda-csi2-imx219-mipi0.dtbo`

Connect the IMX219 to J24 and verify detection:

1	`v4l2-ctl --list-devices`

Configure sensor parameters:

v4l2-ctl -d /dev/v4l-subdev0 --set-ctrl=analogue_gain=200
v4l2-ctl -d /dev/v4l-subdev0 --set-ctrl=exposure=3000

Configure the media pipeline:

media-ctl -d /dev/media0 -V '"imx219 5-0010":0 [fmt:SRGGB8_1X8/1920x1080]'
media-ctl -d /dev/media0 -V '"cdns_csi2rx.4500000.csi-bridge":0 [fmt:SRGGB8_1X8/1920x1080]'
media-ctl -d /dev/media0 -V '"cdns_csi2rx.4500000.csi-bridge":1 [fmt:SRGGB8_1X8/1920x1080]'
media-ctl -d /dev/media0 -V '"4504000.ticsi2rx":0 [fmt:SRGGB8_1X8/1920x1080]'

Capture a JPEG frame:

gst-launch-1.0 v4l2src device=/dev/video0 num-buffers=1 \
  ! "video/x-bayer,width=1920,height=1080,format=rggb,framerate=30/1" \
  ! bayer2rgb ! videoconvert ! jpegenc ! filesink location=cam.jpg

17.2 Scenario B — J25 Camera¶

Edit /boot/uEnv.txt and uncomment the following line (comment out any other name_overlays lines):

1	`name_overlays=ti/k3-j721s2-panda-csi2-imx219-mipi1.dtbo`

Connect the IMX219 to J25 and verify detection:

1	`v4l2-ctl --list-devices`

Configure sensor parameters:

v4l2-ctl -d /dev/v4l-subdev2 --set-ctrl=analogue_gain=200
v4l2-ctl -d /dev/v4l-subdev2 --set-ctrl=exposure=3000

Configure the media pipeline:

media-ctl -d /dev/media0 -V '"imx219 3-0010":0 [fmt:SRGGB8_1X8/1920x1080]'
media-ctl -d /dev/media0 -V '"cdns_csi2rx.4514000.csi-bridge":0 [fmt:SRGGB8_1X8/1920x1080]'
media-ctl -d /dev/media0 -V '"cdns_csi2rx.4514000.csi-bridge":1 [fmt:SRGGB8_1X8/1920x1080]'
media-ctl -d /dev/media0 -V '"4510000.ticsi2rx":0 [fmt:SRGGB8_1X8/1920x1080]'

Capture a JPEG frame:

gst-launch-1.0 v4l2src device=/dev/video2 num-buffers=1 \
  ! "video/x-bayer,width=1920,height=1080,format=rggb,framerate=30/1" \
  ! bayer2rgb ! videoconvert ! jpegenc ! filesink location=cam.jpg

17.3 Scenario C — J24 DSI Display + J25 Camera¶

Edit /boot/uEnv.txt and uncomment the following line (comment out any other name_overlays lines):

1	`name_overlays=ti/k3-j721s2-panda-dsi-rpi-7inch-panel.dtbo ti/k3-j721s2-panda-csi2-imx219-mipi1.dtbo`

For DSI display setup refer to §16. For camera capture commands refer to §17.2.

Warning: The DSI panel must be physically connected to J24 before boot. If the panel is absent, the DSS display subsystem fails to initialize and Mini DisplayPort (J9) will also be unavailable.

18. AI Inference Acceleration¶

The TDA4VE / AM68A SoC includes an 8 TOPS Matrix Multiply Accelerator (MMA). TI provides the TIDL (TI Deep Learning) runtime and model inference tools as part of the Edge AI SDK.

Note: AI inference toolchain documentation and usage examples will be added in a future revision of this guide. Refer to the TI Edge AI documentation and EdgeAI-Studio resources for current information.

Key components:

MMA (Matrix Multiply Accelerator): 8 TOPS, supports INT8 quantized inference
C7x DSP cores: used for pre/post processing in TIDL pipelines
R5F MCU cores: real-time control and sensor management
TIDL runtime: model conversion, inference API, GStreamer integration

19. Troubleshooting¶

19.1 Board Does Not Boot¶

Confirm the SD card is fully inserted into J23 (it clicks into place).
Re-flash the image using Armbian Imager and wait for Write Successful before ejecting.
On first boot, the system expands the filesystem and reboots automatically — allow 3–4 minutes total.
LED indicator: red = powered, OS not running; solid green = OS running.

19.2 No Serial Console Output¶

Verify the adapter is connected to J6, not J5 (USB-C power).
Use a 3.3 V logic USB-to-UART adapter — 5 V signals will damage the board.
Settings: 115200 baud, 8N1, no flow control.
The debug console is on /dev/ttyS2 (UART8).
Open the serial terminal before applying power to capture the full boot log.

19.3 No Network¶

Confirm the RJ45 cable is connected to J1 (Ethernet port).
Check link LED on the Ethernet port.
Verify interface state: nmcli device status
Check assigned IP: ip addr show eth0

19.4 NVMe Not Detected¶

Confirm the FPC cable is fully seated at J10 and the NVMe adapter.
Check kernel messages: dmesg | grep -i nvme
List PCI devices: lspci

19.5 Display No Signal¶

Use a monitor with native DisplayPort input. Passive Mini DP to HDMI adapters do not work.
Confirm the cable is firmly seated in J9.
Check DRM status: cat /sys/class/drm/card*/card*-DP-*/status

Appendix A — Quick Specification Reference¶

Item	Value
SoC	TDA4VE / AM68A (J721S2)
CPU	2× Cortex-A72, up to 2.0 GHz
AI	8 TOPS
RAM	8 GB LPDDR4
Storage	Micro SD (boot + rootfs); PCIe NVMe (expansion)
OS	Armbian (Debian 13 Trixie)
Network	Gigabit Ethernet (eth0), DHCP by default
USB	4× USB 3.0 (TUSB8041 hub)
Display	Mini DisplayPort (J9)
Camera	2× MIPI CSI-2 / DSI FPC (J24, J25)
GPIO header	40-pin, RPi HAT compatible, 3.3 V IO
Debug UART	J6, /dev/ttyS2, 115200 8N1
Power	USB-C (J5), 5 V / 5 A

Document / Resource	Description
Mo 68A Quick Start Guide	Initial setup, flashing, first login
Mo 68A Hardware Reference Manual	Connector pinouts, signal assignments, electrical specifications

Revision History¶

Version	Date	Description
1.0	2026-04-28	Initial release

Mo 68A User Guide¶

Task-based navigation¶

1. Introduction¶

1.1 Product Overview¶

1.2 Key Specifications¶

1.3 Document Scope¶

2. Accessories and Requirements¶

3. Getting Started¶

3.1 Initial Setup¶

3.2 Verify System Status¶

3.3 Recommended Initial Configuration¶

4. Software Management¶

5. Micro SD Card¶

6. Debug Serial Console¶

6.1 Hardware Connection¶

6.2 Terminal Setup¶

7. Mini DisplayPort¶

8. Network and Remote Access¶

8.1 Wired Ethernet¶

8.2 SSH Access¶

9. Fan and Thermal Management¶

9.1 Fan Connector¶

9.2 Automatic Speed Control¶

9.3 Monitoring¶

10. I2C¶

11. RTC¶

11.1 Battery Installation¶

11.2 Time Configuration¶

12. USB¶

12.1 USB 3.0 Type-A Ports¶

12.2 Keyboard and Mouse¶

12.3 USB Audio¶

12.4 USB Drive¶

13. PCIe¶

14. 40-pin GPIO Header¶

14.1 Pin Reference¶

14.2 GPIO¶

14.3 SPI¶

14.4 UART¶

14.5 I2S / Audio¶

14.6 PWM¶

Pin 32 — ECAP0 APWM output¶

Pin 33 — EHRPWM5_B output¶

15. MIPI FPC Ports¶

15.1 Overview¶

15.2 Configuration¶

16. MIPI DSI Display¶

17. Camera Input¶

17.1 Scenario A — J24 Camera¶

17.2 Scenario B — J25 Camera¶

17.3 Scenario C — J24 DSI Display + J25 Camera¶

18. AI Inference Acceleration¶

19. Troubleshooting¶

19.1 Board Does Not Boot¶

19.2 No Serial Console Output¶

19.3 No Network¶

19.4 NVMe Not Detected¶

19.5 Display No Signal¶

Appendix A — Quick Specification Reference¶

Appendix B — Related Documents and Resources¶

Revision History¶