The FTDI Friend from Adafruit (available here) is a highly configurable FTDI serial-to-USB interface. You can use it with the Octavo boards and SOM's from GHI (available here) to connect to UART0 to both debug the booting process and to use as a console for logging into Linux. The advantage of using the UART0 is that network and USB changes will not cause you to lose your console connection. UART0 is also the only source (other than JTAG) of any information about the bootup process. If you have corrupted EEPROM, eMMC or SD images, this is where you will see that information.
The FTDI Friend is configured by default to provide 5V of Vcc output, and 3.3V signal voltage. This is perfect for the AM3358, but check the back of the FTDI friend to make sure it looks like the photo below. We want to be sure it has not been re-configured for 5V signal voltage (the second row of jumper pads). Using 5V signals will damage your AM3358 processor.
The back of the FTDI Friend should look like this:
Connecting the FTDI Friend to UART0:
- Make sure the Octavo board and FTDI Friend are powered off. Use proper ESD protection.
- Place a jumper wire between RTS and CTS on the FTDI Friend
- Connect FTDI Friend GND to Octavo GND (that's GND, SH33 on the GHI OSD3358 board)
- Refer to the photos below for image showing the pin locations on the Adafruit FTDI Friend and the OSD3358 TH
- Connect FTDI Friend TX to UART0 RX (on the GHI OSD3358 TH, that's the pin designated GPIO 1.10 or SH20)
- Connect FTDI Friend RX to UART0 TX (on the GHI OSD3358 TH, that's the pin designated GPIO 1.11 or SH21)
- Note that you can also connect the FTDI to UART1 using the UART1 TX and RX at SH19 and SH18, respectively, but boot time debug output is only available on UART0.
- Connect a USB cable between your computer and the FTDI friend.
- Start the Tera Term (or equivalent) program and connect to the serial port created by the FTDI Friend when it was connected. If you don't know the identity of this serial port, you can run Device Manager (on windows) and look under 'Ports' for the list of serial ports.
- Set the baud rate to 115200, eight data bits, no parity, one stop bit
- To verify the functionality of your terminal software and the FTDI Friend, with the Octavo board powered down, you can place a jumper between TX and RX and you should see anything you type echoed back to you in the terminal window. Be sure to remove this jumper and reconnect to the Octavo board as shown above before powering on the Octavo.
- Apply power to the Octavo board. The first output you see will be information that the Sitara AM3358 chip outputs about its search for bootable media. If your eMMC or SD card is damaged, this is where you will see the diagnostic output
- If you see a series of eight 'C' characters, then the AM3358 was not able to find even the lowest-level bootloader on any media. Your device needs to be re-flashed.
- After the Octava has completed the bootup process, you will see a prompt for your username and password in Tera Term. If you have not changed the password, then the default username and password will be shown above the login prompt.