How to Use the BMP280 Sensor with Shakti Processor?

In this tutorial, the BMP280 Sensor is used with SHAKTI Processor. This sensor can measure barometric pressure and temperature with very good accuracy. As pressure changes with altitude, we can also use it as an altimeter with ±1 meter accuracy. The accuracy of the barometric pressure is ±1 hPa and ±1.0°C for temperature.

Protocol:

The BMP280 sensor works with SPI and I2C protocol. Here, I2C protocol is used. The BMP280 sensor has a 3.3V regulator and level shifting so you can use it with a 3V or 5V logic micro controller without any problems.

Step 1: Requirements

Arty7 35t/100t board with either pinaka, parashu or vajra programmed
BMP280 Sensor.
Micro USB Cable.
Jumper Wires.
shakti-sdk and shakti-tools installed or Platform IO installed and ready

Note: shakti-sdk and shakti-tools are currently a private repository. Please login or sign up to Gitlab and request access here before using it.

Step 2: The Circuit

The I2C connection (SCL and SDA pins) is used.

Connections of the BMP280 sensor:

VCC to 3.3V
GND to GND
SCL to SCL of board
SDA to SDA of board
CSB to 3.3V
SDO to GND

SHAKTI with BMP280 Sensor — Fig. Circuit diagram of BMP280 with Arty7 board

Here we use Arty35t for instance. Also, the connections are the same in Arty100t boards. For better clarity, Check the device pin mapping for pinaka, parashu and vajra

Step 3: Code

Please click here to have a look at the code where temperature and pressure is read from BMP280 sensor using SHAKTI.

Code can be compiled and run using the following ways,

Using terminal on a system with shakti-sdk and shakti-tools installed (Manual method).
Using Platform IO IDE.

Step 4.1: Manual Method

4.1.1 Compile and build

Move to shakti-sdk

cd shakti-sdk

Compile using make software PROGRAM=? TARGET=?. Type make list_applns to list all the applications available in the SDK. Target can be either parashu, pinaka or vajra.

For instance, Use target as parashu,

make software PROGRAM=bmp280 TARGET=parashu

4.1.2 Execution:

Once the application is built, the executable is generated in the output folder. The executable is in ELF file format and they have the extension .shakti. Now, open three terminals, one for each of the following,

One terminal for UART terminal display (miniterm)
Another for OpenOCD.
And the last one for GDB server

Terminal 1: Firstly, Connect to serial output by using miniterm or gtkterm with the baud rate of 19200.

For instance,

$ sudo miniterm.py /dev/ttyUSB1 19200

Note:

“/dev/ttyUSB1” – ttyUSB means “USB serial port adapter”
The “1” (“0” or “1” or “2”“here means the USB device number on your system. The FPGA board is connected to that USB device number.

Terminal 2: After that, Connect to the FPGA board by using the OpenOCD provided by shakti-tools and its respective configuration file. (Read how OpenOCD and RISC-V GDB work together to establish a connection between our PC and the Microprocessor)

For instance, if we use parashu,

$ cd shakti-sdk
$ cd ./bsp/third_party/parashu
$ sudo $(which openocd) -f ftdi.cfg

For pinaka and vajra, Goto cd ./bsp/third_party/<pinaka or vajra>

Terminal 3: Now, open either 32-bit or 64-bit RISC-V GDB based on your architecture i.e riscv32-unknown-elf-gdb or riscv64-unknown-elf-gdb respectively from shakti-tools.

The output executable is created in <path-to-shakti-sdk>/software/examples/i2c_applns/bmp280/output as bmp280.shakti.

Load up the .shakti file by following the below steps. For Parashu,

$ riscv32-unknown-elf-gdb

(gdb) set remotetimeout unlimited
(gdb) target remote localhost:3333
(gdb) file path/to/executable
(gdb) load
(gdb) c

4.1.3 Upload to flash

Steps to generate standalone user application:

The SHAKTI-SDK has a uploader tool that is used to load a content (such as ELF) to flash, after building the image.

Goto the right directory.

    cd shakti-sdk

The make upload command is used to build and upload the application to the flash automatically.

make upload PROGRAM=bmp280 TARGET=parashu

PROGRAM is the new bare metal user application that is created. Type make list_applns to list all the applications available in the SDK.

Step 4.2: Using Platform IO

We can use IDE’s like Platform IO to compile, build, run, upload and debug. Please read the article on Platform IO on SHAKTI to understand the steps.

Miniterm Output

Thus we can read the temperature and the pressure values through the sensor

--- Miniterm on /dev/ttyUSB1: 19200,8,N,1 ---
--- Quit: Ctrl+]  |  Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---                  ((                                          
                                    ,(((((
                                *((((((
                           ./(((((((
                       ./((((((((
                    *(((((((((
                .(((((((((((
             ,((((((((((((
           ((((((((((((((
          .((((((((((((((
              *(((((((((((
                   /(((((((
                  *((((((((
                     *(((((((
                       (((((((((
                        ((((((((((
                         (((((((((((((
                         ((((((((((((((
                        ((((((((((((
                      *(((((((((( 
                    (((((((((               
              *(((((((
           *((((((
       .(((((
   ./(((  
SHAKTI PROCESSORS 
Booting… vspi1.0
Booting on Parashu! hart 0 
Parashu is a SoC build on top of Artix7 100T.
The core belongs to Shakti E class, 32 bit.
Supported ISA: RV32ACIMNU.
Processor Arch ID: 0.
Device ID 1 
extracted device id 2018 
. . . . . . .
Control transferred to RAM
Control: 80808080; Status: 81818181 I2C Initialization success
Initialization BMP280_STATUS_REGISTER Happened Fine

Temperature Value:31.88 °C
The Pressure Value:100.456 Kpa

Temperature Value:31.50 °C
The Pressure Value:100.454 Kpa

Temperature Value:31.52 °C

Miniterm Output (Upload)

Erasing…
Erase complete.
Writing.......
Write complete.
Please reset.

Now press Reset Button on board

--- Miniterm on /dev/ttyUSB1: 19200,8,N,1 ---
--- Quit: Ctrl+]  |  Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---                  ((                                          
                                    ,(((((
                                *((((((
                           ./(((((((
                       ./((((((((
                    *(((((((((
                .(((((((((((
             ,((((((((((((
           ((((((((((((((
          .((((((((((((((
              *(((((((((((
                   /(((((((
                  *((((((((
                     *(((((((
                       (((((((((
                        ((((((((((
                         (((((((((((((
                         ((((((((((((((
                        ((((((((((((
                      *((((((((((
                    (((((((((               
              *(((((((
           *((((((
       .(((((
   ./(((  
SHAKTI PROCESSORS 
Booting… vspi1.0
Booting on Parashu! hart 0 
Parashu is a SoC build on top of Artix7 100T.
The core belongs to Shakti E class, 32 bit.
Supported ISA: RV32ACIMNU.
Processor Arch ID: 0.
Device ID 1 
extracted device id 2018 
. . . . . . .
Control transferred to RAM
Control: 80808080; Status: 81818181 I2C Initialization success
Initialization BMP280_STATUS_REGISTER Happened Fine

Temperature Value:31.88 °C
The Pressure Value:100.456 Kpa

Temperature Value:31.50 °C
The Pressure Value:100.454 Kpa

Akshaya B

Akshaya currently works at the RISE labs. Her favorite subjects are Web designing and Microprocessors. She loves learning about new things and writing about them!