Configuring UART

Raspberry Pi 4

The Raspberry Pi 4 has six available UARTs. By default, only UART1 (used by the debug serial console) is enabled. Note that UART1 uses a different driver than the other UARTs.

If you want to connect your Raspberry Pi 4 with a UART serial peripheral (e.g., a GPS module, lidar module, NFC reader, etc.), then you need to manually enable a UART interface and serial port for the device. To enable UART2 on GPIOs 0 and 1:

1. Set the GPIO pin mode to connect the UART2 hardware block to the GPIO pins:

   gpio-bcm2711 set 0,1 a4

2. Start the serial driver. The address and IRQ are specific for this UART interface:

   devc-serpl011 -b115200 -v -c50000000 -e -F -u2 0xfe201400,153

3. Optionally, configure the serial port settings:

   stty baud=115200 par=none bits=8 stopb=1 < /dev/ser2

You can now try sending data to the serial port with:

echo “Hello World” > /dev/ser2

You can read from the serial port with:

cat /dev/ser2

Additional addresses and IRQs

Use the following table to substitute the appropriate values for the following commands. The filesystem exposes the UART at /dev/ser<Ser#>:

gpio-rp1 set <GPIO #> <GPIO Mode>
devc-serpl011 -b115200 -c50000000 -e -F -u<Ser#> <Address>,<IRQ>

If you also need hardware flow-control (CTS/RTS, i.e., clear to send/request to send), configure those GPIO pins with the second pair of pins listed below for each UART. You can do this at the same time as configuring the TX/RX pins if they use the same alternate mode, or in a separate call to gpio-bcm2711. For example:

# Configure GPIOs for UART0
gpio-bcm2711 set 14,15 a0
gpio-bcm2711 set 16,17 a3

# Configure GPIOs for UART3
gpio-bcm2711 set 4-7 a4

Raspberry Pi 5

To connect your Raspberry Pi 5 with a UART serial peripheral (e.g., a GPS module, lidar module, NFC reader, etc.), you need to manually enable a UART interface and serial port for the device. These instructions explain how to enable UART0 (GPIO pins 14 and 15) on a Raspberry Pi 5:

1. Enable the RP1 MSIX UART0 interrupt:

   msix-rp1 -m set 25l

2. Set the GPIO pin mode to connect the UART0 hardware block to GPIO pins 14 and 15:

   gpio-rp1 set 14,15 a4

3. Start the serial driver. The address and IRQ are specific for this UART interface:

   devc-serpl011-rpi5 -b115200 -v -c50000000 -e -F -u1 0x1f00030000,185

   Note:

   The -u1 option establishes the serial port resource at /dev/ser1 . The -u0 option isn't supported, which is why UART0 is exposed as /dev/ser1 in the filesystem.

4. Optionally, configure the serial port settings:

   stty baud=115200 par=none bits=8 stopb=1 < /dev/ser1

You can now try sending data to the serial port with:

echo “Hello World” > /dev/ser1

You can read from the serial port with:

cat /dev/ser1

Additional addresses and IRQs

Use the following table to substitute the appropriate values for the following commands. The filesystem exposes the UART at /dev/ser<Ser#>:

msix-rp1 -m set <MSIX Interrupt>l
gpio-rp1 set <GPIO #> <GPIO Mode>
devc-serpl011-rpi5 -b115200 -c50000000 -e -F -u<Ser#> <Address>,<IRQ>

If you also need hardware flow-control (CTS/RTS), configure those GPIO pins with the second pair of pins listed below for each UART. You can do this at the same time as configuring the TX/RX pins, or in a separate call to gpio-rp1. For example, to configure UART0 for hardware flow-control, do one of the following:

gpio-rp1 set 14-17 a4

gpio-rp1 set 14,15 a4
gpio-rp1 set 16,17 a4