# Activating additional UARTs on Raspberry Pi 4B **URL:** \ **Category:** Pi Image\ **Created:** [April 21, 2021, 2:25am UTC](https://forum.ubiquityrobotics.com/t/activating-additional-uarts-on-raspberry-pi-4b/807 "2021-04-21T02:25:19Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![astan](https://forum.ubiquityrobotics.com/letter_avatar_proxy/v4/letter/a/5daacb/32.png) [@astan](https://forum.ubiquityrobotics.com/u/astan)\ **Post date:** [April 21, 2021, 2:25am UTC](https://forum.ubiquityrobotics.com/t/activating-additional-uarts-on-raspberry-pi-4b/807/1 "2021-04-21T02:25:19Z")
Device: Raspberry Pi 4B v1.2 Image: 2020-11-07-ubiquity-xenial-lxde Hello all, I’m using the Ubiquity image for a project that does not involve the Magni, and I’d like to enable the additional UART ports available on the RPi 4. I’ve followed the instructions at [https://learn.ubiquityrobotics.com/GPIO\_lines](https://learn.ubiquityrobotics.com/GPIO_lines) to free up the GPIO lines, and I’ve added the following lines to config.txt to enable the four extra uart ports: ``` #Enable the additional uarts for serial communication enable_uart=1 dtoverlay=miniuart-bt dtoverlay=uart2 dtoverlay=uart3 dtoverlay=uart4 dtoverlay=uart5 ``` However, after a reboot, running the command sudo raspi-gpio get returns the following: ``` BANK0 (GPIO 0 to 27): GPIO 00: level=1 fsel=3 alt=4 func=AVEIN_VCLK GPIO 01: level=1 fsel=3 alt=4 func=AVEIN_DSYNC GPIO 02: level=1 fsel=0 alt= func=INPUT GPIO 03: level=1 fsel=0 alt= func=INPUT GPIO 04: level=1 fsel=3 alt=4 func=AVEIN_VID0 GPIO 05: level=1 fsel=3 alt=4 func=AVEIN_VID1 GPIO 06: level=1 fsel=0 alt= func=INPUT GPIO 07: level=1 fsel=0 alt= func=INPUT GPIO 08: level=1 fsel=3 alt=4 func=AVEIN_VID4 GPIO 09: level=1 fsel=3 alt=4 func=AVEIN_VID5 GPIO 10: level=0 fsel=0 alt= func=INPUT GPIO 11: level=0 fsel=0 alt= func=INPUT GPIO 12: level=1 fsel=3 alt=4 func=AVEIN_VID8 GPIO 13: level=1 fsel=3 alt=4 func=AVEIN_VID9 GPIO 14: level=1 fsel=4 alt=0 func=TXD0 GPIO 15: level=1 fsel=4 alt=0 func=RXD0 GPIO 16: level=0 fsel=0 alt= func=INPUT GPIO 17: level=0 fsel=0 alt= func=INPUT GPIO 18: level=0 fsel=0 alt= func=INPUT ... ``` The four pairs of GPIO lines returning functions beginning with ‘AVEIN\_’ should be returning RX and TX like GPIO 14 and 15. I used sudo raspi-gpio funcs to inspect the pin layout returned by raspi-gpio, which returns the following: ``` GPIO, DEFAULT PULL, ALT0, ALT1, ALT2, ALT3, ALT4, ALT5 0, UP, SDA0, SA5, PCLK, AVEOUT_VCLK, AVEIN_VCLK, - 1, UP, SCL0, SA4, DE, AVEOUT_DSYNC, AVEIN_DSYNC, - 2, UP, SDA1, SA3, LCD_VSYNC, AVEOUT_VSYNC, AVEIN_VSYNC, - 3, UP, SCL1, SA2, LCD_HSYNC, AVEOUT_HSYNC, AVEIN_HSYNC, - 4, UP, GPCLK0, SA1, DPI_D0, AVEOUT_VID0, AVEIN_VID0, ARM_TDI 5, UP, GPCLK1, SA0, DPI_D1, AVEOUT_VID1, AVEIN_VID1, ARM_TDO 6, UP, GPCLK2, SOE_N_SE, DPI_D2, AVEOUT_VID2, AVEIN_VID2, ARM_RTCK 7, UP, SPI0_CE1_N, SWE_N_SRW_N, DPI_D3, AVEOUT_VID3, AVEIN_VID3, - 8, UP, SPI0_CE0_N, SD0, DPI_D4, AVEOUT_VID4, AVEIN_VID4, - 9, DOWN, SPI0_MISO, SD1, DPI_D5, AVEOUT_VID5, AVEIN_VID5, - 10, DOWN, SPI0_MOSI, SD2, DPI_D6, AVEOUT_VID6, AVEIN_VID6, - 11, DOWN, SPI0_SCLK, SD3, DPI_D7, AVEOUT_VID7, AVEIN_VID7, - 12, DOWN, PWM0, SD4, DPI_D8, AVEOUT_VID8, AVEIN_VID8, ARM_TMS 13, DOWN, PWM1, SD5, DPI_D9, AVEOUT_VID9, AVEIN_VID9, ARM_TCK 14, DOWN, TXD0, SD6, DPI_D10, AVEOUT_VID10, AVEIN_VID10, TXD1 15, DOWN, RXD0, SD7, DPI_D11, AVEOUT_VID11, AVEIN_VID11, RXD1 16, DOWN, FL0, SD8, DPI_D12, CTS0, SPI1_CE2_N, CTS1 17, DOWN, FL1, SD9, DPI_D13, RTS0, SPI1_CE1_N, RTS1 18, DOWN, PCM_CLK, SD10, DPI_D14, I2CSL_SDA_MOSI, SPI1_CE0_N, PWM0 ... ``` So it appears that funcs is returning the wrong GPIO pin setup for the Pi 4B. Has anyone successfully gotten uart2-uart5 working on a Ubiquity Pi image? Is there something I can do to force raspi-gpio to recognize that it is a Pi4B with a bcm2711 and use the appropriate pin setup? Any help would be appreciated. ---
**Author:** ![astan](https://forum.ubiquityrobotics.com/letter_avatar_proxy/v4/letter/a/5daacb/32.png) [@astan](https://forum.ubiquityrobotics.com/u/astan)\ **Post date:** [April 24, 2021, 4:21am UTC](https://forum.ubiquityrobotics.com/t/activating-additional-uarts-on-raspberry-pi-4b/807/2 "2021-04-24T04:21:53Z")
In case anyone in the future is wondering, building the newest version of raspi-gpio from source using the instructions on the GitHub page and adding the directory to the start of the PATH fixed the pin mapping. After a reboot, a loopback test confirmed all five serial ports were functioning as expected. Thanks to the crew at Ubiquity for making this image freely available. ---
**Author:** ![mjstn2011](https://forum.ubiquityrobotics.com/user_avatar/forum.ubiquityrobotics.com/mjstn2011/32/30_2.png) [@mjstn2011](https://forum.ubiquityrobotics.com/u/mjstn2011)\ **Post date:** [April 24, 2021, 6:10am UTC](https://forum.ubiquityrobotics.com/t/activating-additional-uarts-on-raspberry-pi-4b/807/3 "2021-04-24T06:10:09Z")
This is very helpful @astan thank you for following up and finding a fix. I had duplicated your earlier problem but had not dug in to look for a solution yet. Thanks for the followup post as I had known more ports were possible on the Pi4 but had not tried it yet. ---
**Author:** ![mjstn2011](https://forum.ubiquityrobotics.com/user_avatar/forum.ubiquityrobotics.com/mjstn2011/32/30_2.png) [@mjstn2011](https://forum.ubiquityrobotics.com/u/mjstn2011)\ **Post date:** [April 24, 2021, 6:48am UTC](https://forum.ubiquityrobotics.com/t/activating-additional-uarts-on-raspberry-pi-4b/807/4 "2021-04-24T06:48:36Z")
I hit another thing requiring a small hack. The apt get of automake gave me a rev 1.15 and the aclocal.m4 that is included in the raspi-gpio repository was setup to require automake 1.16. So I removed aclocal.m4, edit configure and change rev like this: am\_\_api\_version=‘1.15’ I pulled src with: git clone [https://github.com/RPi-Distro/raspi-gpio](https://github.com/RPi-Distro/raspi-gpio) Then I could do the make as per the github for raspi-gpio and was able to enable a port, in my case uart3. Thought this mention may help others to fix this make issue. Thanks. ---
**Author:** ![astan](https://forum.ubiquityrobotics.com/letter_avatar_proxy/v4/letter/a/5daacb/32.png) [@astan](https://forum.ubiquityrobotics.com/u/astan)\ **Post date:** [April 24, 2021, 9:33am UTC](https://forum.ubiquityrobotics.com/t/activating-additional-uarts-on-raspberry-pi-4b/807/5 "2021-04-24T09:33:05Z")
Hi Mark! I owe you and your team 16.04 beers for solving the “Ubuntu 16.04 isn’t compatible with RPi 4B” problem, but your buy us a beer link at [https://www.ubiquityrobotics.com/dl-thank-you/](https://www.ubiquityrobotics.com/dl-thank-you/) appears to be broken. Please advise. ---
**Author:** ![mjstn2011](https://forum.ubiquityrobotics.com/user_avatar/forum.ubiquityrobotics.com/mjstn2011/32/30_2.png) [@mjstn2011](https://forum.ubiquityrobotics.com/u/mjstn2011)\ **Post date:** [April 25, 2021, 9:33am UTC](https://forum.ubiquityrobotics.com/t/activating-additional-uarts-on-raspberry-pi-4b/807/6 "2021-04-25T09:33:37Z")
Thank you. I have passed this on to our web guy. This is some sort of effect due to some recent web site change. Thanks for pointing this out ---
**Author:** ![rohbotics](https://forum.ubiquityrobotics.com/user_avatar/forum.ubiquityrobotics.com/rohbotics/32/222_2.png) [@rohbotics](https://forum.ubiquityrobotics.com/u/rohbotics)\ **Post date:** [April 25, 2021, 7:02pm UTC](https://forum.ubiquityrobotics.com/t/activating-additional-uarts-on-raspberry-pi-4b/807/7 "2021-04-25T19:02:16Z")
For now the Donate button on the other downloads page should work: [https://downloads.ubiquityrobotics.com/pi.html](https://downloads.ubiquityrobotics.com/pi.html) Thanks Rohan