stm32f401rc-rs485

This page discusses issues unique to NuttX configurations for the NuttX STM32F4-RS485 development board.

../../../../../_images/stm32f401rc_rs485.jpg

Board information

This board was release on NuttX International Workshop 2023 and developed based on STM32F401RCT6 microcontroller.

STM32F401RCT6 microcontroller features:
  • Arm 32-bit Cortex®-M4 CPU with FPU

  • 256 Kbytes of Flash memory

  • 64 Kbytes of SRAM

  • Serial wire debug (SWD) & JTAG interfaces

  • Up to 81 I/O ports with interrupt capability

  • Up to 11 communication interfaces

  • Up to 3 I2C interfaces

  • Up to 3 USARTs

  • Up to 4 SPIs

  • SDIO interface

  • USB 2.0 full-speed device/host/OTG controller with on-chip PHY

The board features:

  • Digital I2C Temperature Sensor (TMP75)

  • 2K bits (256x8) I2C EEPROM

  • On-board RS485 Transceiver

  • Two Analog Input Stages with Amplifier Buffer

  • Two Analog Output Stages with Amplifier Buffer

  • MicroSD Connector supporting 1 or 4-bit bus

  • Four User LEDs

  • Four User Buttons

  • USB for DFU (Device Firmware Update) and USB device functionality, as well as powering the board

  • Onboard voltage regulator from 5V to 3.3V

  • SWD Pins for use as STLink (Pin header) and TC2030-IDC 6-Pin Tag-Connect Plug-of-Nails™ Connector

  • Crystal for HS 8MHz

  • Crystal for RTC 32.768KHz

Board documentation: https://github.com/lucaszampar/NuttX_STM32F4_RS485_DevBoard

As F4 series have a USB DFuSe-capable BootROM [AN2606], the board can be flashed via dfu-util over USB, or via stm32flash over UART without any debuggers.

LEDs

The STM32F4-RS485 has 4 software controllable LEDs.

LED

PINS

LED_1

PC0

LED_2

PC1

LED_4

PC2

LED_5

PC3

User Buttons

The STM32F4-RS485 has 4 user switches.

SWITCH

PINS

LABEL

SWIO_1

PB13

SW3

SWIO_2

PB14

SW4

SWIO_3

PB15

SW5

SWIO_4

PC6

SW6[1]

[1] The switch SWIO_4 (SW6) is disabled due a conflict with PIN PC6 when using USART6.

UARTs

The STM32F4-RS485 has 1 USART available for user.

USART6

UART/USART

PINS

TX

PC6 [1]

RX

PC7

CK

PA8

[1] Warning you make need to reverse RX/TX on some RS-232 converters

SDCard support

The STM32F4-RS485 has 1 SDCard slot connected as below:

SDIO

PINS

SDIO_D0

PC8

SDIO_D1

PC9

SDIO_D2

PC10

SDIO_D3

PC11

SDIO_DK

PC12

EEPROM

The STM32F4-RS485 development board has serial EEPROM HX24LC02B, with 2k bits (256x8) and internally organized with 32 pages of 8 bytes each. It is connected through I2C as below:

I2C

PINS

SDA

PB7

SCL

PB8

Users can enable EERPOM support on STM32F4-RS485 by following below configuration:

  • Configure basic nsh:

    ./tools/configure.sh -l stm32f401rc-rs485:nsh
    
  • Enable the following configs:

    CONFIG_DEV_ZERO=y
    CONFIG_EEPROM=y
    CONFIG_FS_PROCFS=y
    CONFIG_I2C=y
    CONFIG_I2C_EE_24XX=y
    CONFIG_STM32_I2C1=y
    
  • Build and flash the STM32F4-RS485.

  • Use dd command to write and read data from EEPROM as below:

    nsh> dd if=/dev/zero of=/dev/eeprom
    nsh: dd: write failed: 1
    nsh> dd if=/dev/console of=/dev/eeprom bs=1 count=4
    (type "Hello")
    nsh> dd if=/dev/eeprom of=/dev/console bs=4 count=1
    Hellonsh>
    

Temperature Sensor

The STM32F4-RS485 development board has a temperature sensor TMP75 (compatible with LM75) connected through I2C as below:

I2C

PINS

SDA

PB7

SCL

PB8

RS485 Transceiver

The STM32F4-RS485 development board has a half-duplex RS-485 transceiver, the BL3085B it is connected through USART2 as below:

USART2

PINS

USART2_RX

RO

USART2_RTS

DE, /RE

USART2_RX

DI

A/D Converter

The STM32F4-RS485 development board has two Analog to Digital converters with Amplifier Buffer (1COS724SR) and connected as below:

PWM

PINS

PWM_1

PB6

PWM_2

PA6

D/C Converter

The STM32F4-RS485 development board has two Digital to Analog converters with Amplifier Buffer (1COS724SR) and connected as below:

ADC

PINS

ADC_1

PA0

ADC_2

PA4

Configurations

Each stm32f401rc-rs485 configuration is maintained in a sub-directory and can be selected as follow:

tools/configure.sh stm32f401rc-rs485:<subdir>

Where <subdir> is one of the following:

Configuration Directories

nsh

Configures the NuttShell (nsh) located at apps/examples/nsh. This configuration enables a serial console on USART6.

usbnsh

Configures the NuttShell (nsh) located at apps/examples/nsh. This configuration enables a serial console over USB.

After flasing and reboot your board you should see in your dmesg logs:

[ 2638.948089] usb 1-1.4: new full-speed USB device number 16 using xhci_hcd
[ 2639.054432] usb 1-1.4: New USB device found, idVendor=0525, idProduct=a4a7, bcdDevice= 1.01
[ 2639.054437] usb 1-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 2639.054438] usb 1-1.4: Product: CDC/ACM Serial
[ 2639.054440] usb 1-1.4: Manufacturer: NuttX
[ 2639.054441] usb 1-1.4: SerialNumber: 0
[ 2639.074861] cdc_acm 1-1.4:1.0: ttyACM0: USB ACM device
[ 2639.074886] usbcore: registered new interface driver cdc_acm
[ 2639.074887] cdc_acm: USB Abstract Control Model driver for USB modems and ISDN adapters

You may need to press ENTER 3 times before the NSH show up.

sdcard

Configures the NuttShell (nsh) and enables SD card support. The stm32f401rc-rs485 has an onboard microSD slot that should be automatically registered as the block device /dev/mmcsd0 when an SD card is present. The SD card can then be mounted by the NSH commands:

nsh> mount -t procfs /proc
nsh> mount -t vfat /dev/mmcsd0 /mnt

modbus_slave

Configures the NuttShell (nsh) and enables modbus in slave mode. This configuration enables a serial console on USART6. The RS-485 is connected to USART2. Follow below precedure to use modbus test aplication, you will need a USB to RS-485 converter to connect the board to a PC via RS-485.

NuttShell configuration:

Run modbus application at NSH:

nsh> modbus -help
USAGE: modbus [-d|e|s|q|h]

Where:
  -d : Disable protocol stack
  -e : Enable the protocol stack
  -s : Show current status
  -q : Quit application
  -h : Show this information

nsh> modbus -e

PC Configuration:

Download and install mbpoll aplication:

sudo apt install mbpoll

Check which TTY USB port is being used by you USB to RS-485 converter:

sudo dmesg
[99846.668209] usb 1-1.3: Product: USB Serial
[99846.676313] ch341 1-1.3:1.0: ch341-uart converter detected
[99846.677454] usb 1-1.3: ch341-uart converter now attached to ttyUSB1

Run the mbpoll as below:

mbpoll -a 10 -b 38400 -t 3 -r 1000 -c 4 /dev/ttyUSB1 -R

At PC terminal you will see the mbpoll application receiving the random values generated by STM32F401RC-RS485 and transmitted over RS-485:

mbpoll 1.0-0 - FieldTalk(tm) Modbus(R) Master Simulator
Copyright © 2015-2019 Pascal JEAN, https://github.com/epsilonrt/mbpoll
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions; type 'mbpoll -w' for details.

Protocol configuration: Modbus RTU
Slave configuration...: address = [10]
                        start reference = 1000, count = 4
Communication.........: /dev/ttyUSB1,      38400-8E1
                        t/o 1.00 s, poll rate 1000 ms
Data type.............: 16-bit register, input register table
-- Polling slave 10... Ctrl-C to stop)
[1000]:  58080 (-7456)
[1001]:  0
[1002]:  0
[1003]:  0
-- Polling slave 10... Ctrl-C to stop)
[1000]:  6100
[1001]:  0
[1002]:  0
[1003]:  0
-- Polling slave 10... Ctrl-C to stop)
[1000]:  51010 (-14526)
[1001]:  0
[1002]:  0
[1003]:  0
-- Polling slave 10... Ctrl-C to stop)
[1000]:  12528
[1001]:  0
[1002]:  0
[1003]:  0

modbus_master

Configures the NuttShell (nsh) and enables modbus in master mode. This configuration enables a serial console on USART6. The RS-485 is connected to USART2. Follow below precedure to use modbusmaster test aplication, you will need a USB to RS-485 converter to connect the board to a PC via RS-485.

PC Configuration:

Download and install diagslave aplication from https://www.modbusdriver.com/diagslave.html.

Check which TTY USB port is being used by you USB to RS-485 converter:

sudo dmesg
[99846.668209] usb 1-1.3: Product: USB Serial
[99846.676313] ch341 1-1.3:1.0: ch341-uart converter detected
[99846.677454] usb 1-1.3: ch341-uart converter now attached to ttyUSB1

Run the diagslave as below:

sudo diagslave -a 10 -b 38400 /dev/ttyUSB1

At PC terminal you will see the diagslave application listening to address 10, notice that this address is configurable via MODBUSMASTER_SLAVEADDR:

diagslave 3.4 - FieldTalk(tm) Modbus(R) Diagnostic Slave Simulator
Copyright (c) 2002-2021 proconX Pty Ltd
Visit https://www.modbusdriver.com for Modbus libraries and tools.

Protocol configuration: Modbus RTU, frame tolerance = 0ms
Slave configuration: address = 10, master activity t/o = 3.00s
Serial port configuration: /dev/ttyUSB1, 38400, 8, 1, even

Server started up successfully.
Listening to network (Ctrl-C to stop)
Slave  10: readHoldingRegisters from 2, 1 references
.......

NuttShell configuration:

Run modbusmaster application at NSH:

NuttShell (NSH) NuttX-12.4.0
nsh> modbusmaster
Initializing modbus master...
Creating poll thread.
Sending 100 requests to slave 10
mbmaster_main: Exiting poll thread.
Modbus master statistics:
Requests count:  100
Responses count: 100
Errors count:    0
Deinitializing modbus master...

The application modbusmaster will send 100 requests, you can check on diagslave:

Server started up successfully.
Listening to network (Ctrl-C to stop)
Slave  10: readHoldingRegisters from 2, 1 references
Slave  10: readHoldingRegisters from 2, 1 references
Slave  10: readHoldingRegisters from 2, 1 references
Slave  10: readHoldingRegisters from 2, 1 references
Slave  10: readHoldingRegisters from 2, 1 references
Slave  10: readHoldingRegisters from 2, 1 references
Slave  10: readHoldingRegisters from 2, 1 references

lm75

Configures the NuttShell (nsh) over USB Serial (check usbserial configuration) and enables temperature sensor LM75. NSH commands:

nsh> lm75 -help
Usage: temp [OPTIONS]
  [-n count] selects the samples to collect.  Default: 1 Current: 100
  [-h] shows this message and exits
nsh> lm75 -n 3
30.13 degrees Celsius
30.13 degrees Celsius
30.13 degrees Celsius

adc

Configures the NuttShell (nsh) over USB Serial (check usbserial configuration) and enables ADC 1 on channels 0 and 4. NSH commands:

nsh> adc -h
Usage: adc [OPTIONS]

Arguments are "sticky".  For example, once the ADC device is
specified, that device will be re-used until it is changed.

"sticky" OPTIONS include:
  [-p devpath] selects the ADC device.  Default: /dev/adc0 Current: /dev/adc0
  [-n count] selects the samples to collect.  Default: 1 Current: 0
  [-h] shows this message and exits
nsh> adc -n 2
adc_main: g_adcstate.count: 2
adc_main: Hardware initialized. Opening the ADC device: /dev/adc0
Sample:
1: channel: 0 value: 2684
Sample:
1: channel: 4 value: 2682

Currently there is a bug that causes the application to always read the same value for channel 0 and 4. If you want to read the value from channel 2, you will need to enable the config “ADC1 Scan Mode”.

dac

Configures the NuttShell (nsh) over USB Serial (check usbserial configuration) and enables PWM 3 on channel 1. Use pwm command on NSH to change dutty cycle, frequency and duration, use dac_out_2 to measure the output voltage. NSH commands:

nsh> pwm -h
Usage: pwm [OPTIONS]

Arguments are "sticky".  For example, once the PWM frequency is
specified, that frequency will be re-used until it is changed.

"sticky" OPTIONS include:
  [-p devpath] selects the PWM device.  Default: /dev/pwm0 Current: NONE
  [-f frequency] selects the pulse frequency.  Default: 100 Hz Current: 100 Hz
  [-d duty] selects the pulse duty as a percentage.  Default: 50 % Current: 50 %
  [-t duration] is the duration of the pulse train in seconds.  Default: 5 Current: 5
  [-h] shows this message and exits
nsh> pwm -d 50 -t 3
pwm_main: starting output with frequency: 50 duty: 00007fff
pwm_main: stopping output

qencoder

Configures the NuttShell (nsh) over USB Serial (check usbserial configuration) and enables Timer 3 on channels 1 and 2 to handle Quadrature Encoder. NSH commands:

nsh> qe -help

Usage: qe [OPTIONS]

OPTIONS include:
  [-p devpath] QE device path
  [-n samples] Number of samples
  [-t msec]    Delay between samples (msec)
  [-r]         Reset the position to zero
  [-h]         Shows this message and exits
  nsh> qe -p /dev/qe0 -n 5 -t 100 -r
  nsh: qe: too many arguments
  qe_main: Hardware initialized. Opening the encoder device: /dev/qe0
  qe_main: Resetting the count...
  qe_main: Number of samples: 5
  qe_main:   1. 0
  qe_main:   2. 0
  qe_main:   3. 4
  qe_main:   4. 2
  qe_main:   5. 2
  Terminating!