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linux-serial-si4455

This is a serial port driver for Silicon Labs Si4455 Sub-GHz transciver.

The goal of this driver is to removing wires between central(linux) device and remote serial devices/sensors, but keeping the original user software. It represents regular serial interface for the user space.

[0] - Datasheet: https://www.silabs.com/documents/public/data-sheets/Si4455.pdf

Additional readings:

Table of contents

1. Building

1.1. Prerequirements

sudo apt install git bc bison flex libssl-dev libncurses5-dev

1.2. Compile

git clone https://github.com/dministro/linux-serial-si4455
cd linux-serial-si4455/src/linux/drivers/tty/serial
make -C /path/to/kernel/source M=$(pwd) modules

2. Interfaces

2.1. Device tree bindings

You can see the required parameters in silabs,si4455.yaml

2.2. Device configuration(firmware)

2.2.1. Prerequirements

To generate radio configuration, the Silicon Labs Wireless Development Suite is required.

2.2.2. Generate

Before you start, see ref: [2]

  1. Start WDS
  2. Select Simulate radio option on startup screen
  3. Select Si4455 and revision you have in Select Radio dialog

It is important to select the proper revision, because the generated configuration is different between revision B1 and C2.

  1. Select Radio Configuration Application in Application Manager
  2. Select Bidirectional packet project in Radio Configuration Application dialog.
  3. Make your project specific configuration.
    You can find some configuration file under wds_examples directory
  4. Click Generate source than choose Save custom radio configuration header file

2.2.3. Compile

cd fw
make FW_NAME=test.bin \
RADIO_CONFIG=../wds_examples/radio_config_si4455_revb1_ook_bidirectional_packet_15.h \
firmware

The resulting configuration file path: build/test.bin

Parameters:

  • RADIO_CONFIG: path to radio configuration header generated by WDS
  • FW_NAME: the resulting file name
  • FW_PREFIX: firmware installation path in case of firmware-install rule.
    default: /lib/firmware

Rules:

  • firmware: compiles the firmware binary file
  • firmware-install: firmware rule plus installs the firmware binary under the given FW_PREFIX

2.3. device

The driver instances are comes up under /dev as

/dev/ttySSiX

, where X is the index of instance.

The driver supports only:

  • Char size: 8 bits
  • Handshake: None or RTSCTS.
    RTSCTS preferred

2.4. sysfs

The si4455 driver uses configuration parameters and maintains statistics inside sysfs filesystem.

current_rssi

Path:

/sys/class/tty/ttySSiX/device/current_rssi

Description:

Shows the latest rssi value measured by chip.
To convert the value to dBm. See chapter 3.2.1. Received Signal Strength Indicator in [0]

package_size

Path:

/sys/class/tty/ttySSiX/device/package_size

Description:

Shows or stores the package size.
The new value applied immediately.
Variable package size (package_size = 0)

rx_channel

Path:

/sys/class/tty/ttySSiX/device/rx_channel

Description:

Shows or stores the receive channel index.
The new value applied immediately.

tx_channel

Path:

/sys/class/tty/ttySSiX/device/tx_channel

Description:

Shows or stores transmit channel index.
The new value will be used on next data transmit.

tx_timeout

Path:

/sys/class/tty/ttySSiX/device/tx_timeout

Description:

Shows or stores the transmit timeout.
The new value will be used on next data transmit.

2.5. debugfs

The si4455 driver maintains statistics inside debugfs filesystem.

cts_error_count

Path:

/sys/kernel/debug/spiX.Y/si4455/cts_error_count

Description:

The numer of cts timeouts. In case of cts timeout, the driver reinitialize the chip.

tx_error_count

Path:

/sys/kernel/debug/spiX.Y/si4455/tx_error_count

Description:

The number of tx timeouts. In case of tx timeout, the driver restarts the last data transmission.

chip_rev Path:

/sys/kernel/debug/spiX.Y/si4455/partinfo/chip_rev

Description:

The value of CHIPREV field in PART_INFO structure.
See PART_INFO command details in [3] or in [4]

rom_id Path:

/sys/kernel/debug/spiX.Y/si4455/partinfo/rom_id

Description:

The value of ROMID field in PART_INFO structure.
See PART_INFO command details in [3] or in [4]
See ref [5]

part Path:

/sys/kernel/debug/spiX.Y/si4455/partinfo/part

Description:

The value of PART field in PART_INFO structure.
See PART_INFO command details in [3] or in [4]
See ref [5]

3. Sample setup with Raspberry Pi 3

Sample setup with Raspberry Pi 3

Wiring:

Raspberry Pi Function Color ZETA-433
17 3V3 red 4
19 SPI0 MOSI yellow 10
21 SPI0 MISO orange 11
23 SPI0 SCLK green 9
25 GND black 2
26 SPI0 CE1 grey 12
38 GPIO 20 interrupt brown 5
40 GPIO 21 shutdown white 3

3.1. Building

3.1.1 Prerequirements

To compile si4455 kernel module on a Raspbian target the proper version of kernel source is required.
See: https://github.com/RPi-Distro/rpi-source

sudo apt install git bc bison flex libssl-dev libncurses5-dev

3.1.1 Compile

For the setup above:

cd rpi_setup
make \
OL_BUS=0 \
OL_DEV=1 \
OL_SDN=21 \
OL_IRQ=20 \
OL_PACKAGE_SIZE=0 \
RADIO_CONFIG=../wds_examples/radio_config_si4455_revc2_ook_bidirectional_packet_variable.h \
all

Parameters:

  • OL_BUS: spi bus index
    default: 0
  • OL_DEV: spi device index
    default: 1
  • OL_SDN: shutdown gpio index
    default: 21
  • OL_IRQ: interrupt gpio index
    default: 20
  • OL_PACKAGE_SIZE: package size configured in WDS. 0 means variable package size.
    default: 15
  • OL_TX_CHANNEL: transmit channel
    default: 3
  • OL_RX_CHANNEL: receive channel
    default: 3
  • OL_TX_TIMEOUT: transmit timeout(ms)
    default: 100
  • RADIO_CONFIG: path to radio configuration header generated by WDS
  • OL_FW_NAME: generated firmware file name.
    default: si4455_spi$(OL_BUS)_$(OL_DEV).ez.bin

Rules:

  • driver: compiles the kernel module(si4455.ko)
  • driver-install: driver rule plus copies the si4455.ko under /lib/modules/$(uname -r)/extra, then invokes depmod.
    Requires: root privilages
  • firmware: compiles the firmware binary file
  • firmware-install: firmware rule plus installs the firmware binary under /lib/firmware.
    Requires: root privilages
  • overlay: generates and compiles device tree bindings overlay.
    Generated overlay name(under output/overlay/build): si4455_spi$(OL_BUS)_$(OL_DEV).dtbo
  • overlay-install: overlay rule plus installs the overlay under /boot/overlays.
    Requires: root privilages
  • boot-configure: enables the spi port and adds the overlay in /boot/config.txt.
    Requires: root privilages
  • install: driver-install, firmware-install and overlay-install rules.
    Requires: root privilages
  • all: install and boot-configure rules.
    Requires: root privilages

4. Testing

Test setup with Raspberry Pi 3

BOM:

Wiring:

Raspberry Pi Function ZETA-433 #0 ZETA-433 #1
17 3V3 4 4
19 SPI0 MOSI 10 10
21 SPI0 MISO 11 11
23 SPI0 SCLK 9 9
25 GND 2 2
24 SPI0 CE0 12 -
16 GPIO 23 interrupt 5 -
18 GPIO 24 shutdown 3 -
26 SPI0 CE1 - 12
38 GPIO 20 interrupt - 5
40 GPIO 21 shutdown - 3

4.1. Compiling

For ZETA-433 #0:

cd rpi_setup
make \
OL_BUS=0 \
OL_DEV=0 \
OL_SDN=24 \
OL_IRQ=23 \
OL_PACKAGE_SIZE=0 \
RADIO_CONFIG=../wds_examples/radio_config_si4455_revc2_ook_bidirectional_packet_variable.h \
all

For ZETA-433 #1:

cd rpi_setup
make \
OL_BUS=0 \
OL_DEV=1 \
OL_SDN=21 \
OL_IRQ=20 \
OL_PACKAGE_SIZE=0 \
RADIO_CONFIG=../wds_examples/radio_config_si4455_revc2_ook_bidirectional_packet_variable.h \
all

4.2. Testing

After compiling, restart is required to load overlays.

If probe success after boot, dmesg:
dmesg

The new devices are under /dev:
ls -la /dev | grep ttySSi

If the new devices are visible under /dev, they are ready to use as a serial device.
Testing with minicom or tio:

tio -f none /dev/ttySSi0
tio -f none /dev/ttySSi0

minicom -c on -D /dev/ttySSi1
minicom -c on -D /dev/ttySSi1