How to read values using GPIO with Shakti Processor?

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In this tutorial, we will use the GPIO code to read each switch value. GPIO stands for general-purpose input/output. GPIO pins have no specific functions, thus making them multifunctional. You can connect a device to a specific GPIO pin and control it with a software program.

Step 1: What You Will Need

  • Arty7 35t/100t board with either pinaka, parashu or vajra programmed
  • A Switch.
  • 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

For Read GPIO, the switch is connected to GPIO pins.

  • GPIOn (n=0, 1, ..) to button (one leg)
  • Button (second leg) to Vcc 
Fig. The circuit diagram of SHAKTI (Arty7 100t) for read GPIO

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

Step 3: Code

Please click here and have a look at the code.


Code can be compiled and run using the following ways,


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 = rdgpio 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 GDB server
  • And the last one for OpenOCD.

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/gpio_applns/rdgpio/output as rdgpio.shakti.

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

$ 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 = rdgpio 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

--- 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
Read Data is :2

Miniterm Output (Upload)

Erasing…
Erase complete.
Writing......
Write complete.
Please reset.
  • Now press Reset Button on board
                                        ((                                          
                                    ,(((((
                                *((((((
                           ./(((((((
                       ./((((((((
                    *(((((((((
                .(((((((((((
             ,((((((((((((
           ((((((((((((((
          .((((((((((((((
              *(((((((((((
                   /(((((((
                  *((((((((
                     *(((((((
                       (((((((((
                        ((((((((((
                         (((((((((((((
                         ((((((((((((((
                        ((((((((((((
                      *((((((((((
                    (((((((((               
              *(((((((
           *((((((
       .(((((
   ./(((  
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
Read Data is :2

This Post Has One Comment

  1. Dishant Shah

    Hello, please elaborate how other GPIOs can be used using the rdgpio code instead of the default one.

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