Communication/Spi/render.cpp

Reading a SPI device on the Bela Mini

This sketch initialises the second SPI device (SPI1) on the Bela Mini, and reads data from it.

The SPI pins are: P2-25: MOSI P2-27: MISO P2-29: CLK P2-31: CS

To enable these pins for SPI you must first run the following commands (e.g.: in the console at the bottom of the Bela IDE, or via ssh)

config-pin P2.25 spi config-pin P2.27 spi config-pin P2.29 spi_sclk config-pin P2.31 spi_cs

The SPI readouts are then performed in an Auxiliary Task, seperate from the real-time audio thread.

/*
 ____  _____ _        _
| __ )| ____| |      / \
|  _ \|  _| | |     / _ \
| |_) | |___| |___ / ___ \
|____/|_____|_____/_/   \_\
http://bela.io
*/
/*
MIT License
 
Copyright (c) 2020 Jeremiah Rose
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
 
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/
 
#include <Bela.h>
#include <stdio.h>
#include <libraries/Spi/Spi.h>
 
// Create a seperate thread to poll Spi from
AuxiliaryTask SpiTask;
void readSpi(void*); // Function to be called by the thread
float readInterval = 0.5;// How often readSpi() is run (in seconds)
 
int readCount = 0; // Used for scheduling, do not change
int readIntervalSamples; // How many samples between, do not change
 
Spi spiDevice;
 
unsigned char exampleOutput;
 
bool setup(BelaContext *context, void *userData)
{
        spiDevice.setup({
                        .device = "/dev/spidev2.1", // Device to open
                        .speed = 500000, // Clock speed in Hz
                        .delay = 0, // Delay after last transfer before deselecting the device
                        .numBits = 8, // No. of bits per transaction word
                        .mode = Spi::MODE3 // Spi mode
                        });
 
        // Set up auxiliary task to read Spi outside of the real-time audio thread:
        SpiTask = Bela_createAuxiliaryTask(readSpi, 50, "bela-Spi");
        readIntervalSamples = context->audioSampleRate * readInterval;
        return true;
}
 
// Runs every audio frame
void render(BelaContext *context, void *userData)
{
        // Runs every audio sample
        for(unsigned int n = 0; n < context->audioFrames; n++) {
 
                // Schedule auxiliary task for Spi readings
                if(++readCount >= readIntervalSamples) {
                        readCount = 0;
                        Bela_scheduleAuxiliaryTask(SpiTask);
                }
 
                // use Spi output for whatever you need here
                // exampleCalculation = (int) exampleOutput + 1;
        }
}
 
// Auxiliary task to read Spi
void readSpi(void*)
{
        // Example transmission
        int transmissionLength = 4; // Number of bytes to send/receive
        unsigned char Tx[transmissionLength]; // Buffer to send
        unsigned char Rx[transmissionLength]; // Buffer to receive into
        Tx[0] = 0xff; // Fill each byte of the send buffer
        Tx[1] = 0x22;
        Tx[2] = 0xff;
        Tx[3] = 0x0;
 
        if (spiDevice.transfer(Tx, Rx, transmissionLength) == 0)
        {
                // Print result
                printf("Spi: Transaction Complete. Sent %d bytes, received: ", transmissionLength);
                int n = 0;
                for(n = 0; n < transmissionLength; ++n)
                        printf("%#02x ", Rx[n]);
                printf("\n");
 
                // Process received buffer. In this example we just send the first byte
                // to the audio thread via the global variable exampleOutput
                exampleOutput = Rx[0];
        }
        else
                fprintf(stderr, "Spi: Transaction Failed\r\n");
}
 
void cleanup(BelaContext *context, void *userData)
{
}