Initial Release

spi/mpu9250_spi/CMakeLists.txt

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+add_executable(mpu9250_spi
+        mpu9250_spi.c
+        )
+
+# Pull in our (to be renamed) simple get you started dependencies
+target_link_libraries(mpu9250_spi pico_stdlib hardware_spi)
+
+# create map/bin/hex file etc.
+pico_add_extra_outputs(mpu9250_spi)
+
+# add url via pico_set_program_url
+example_auto_set_url(mpu9250_spi)

spi/mpu9250_spi/README.adoc

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+= Attaching a MPU9250 accelerometer/gyroscope via SPI
+
+This example code shows how to interface the Raspberry Pi Pico to the MPU9250 accelerometer/gyroscope board. The particular device used can be interfaced via I2C or SPI, we are using SPI, and interfacing at 3.3v.
+
+[NOTE]
+======
+This is a very basic example, and only recovers raw data from the sensor. There are various calibration options available that should be used to ensure that the final results are accurate. It is also possible to wire up the interrupt pin to a GPIO and read data only when it is ready, rather than using the polling approach in the example.
+======
+
+== Wiring information
+
+Wiring up the device requires 6 jumpers as follows:
+
+   * GPIO 4 (pin 6) MISO/spi0_rx-> ADO on MPU9250 board
+   * GPIO 5 (pin 7) Chip select -> NCS on MPU9250 board
+   * GPIO 6 (pin 9) SCK/spi0_sclk -> SCL on MPU9250 board
+   * GPIO 7 (pin 10) MOSI/spi0_tx -> SDA on MPU9250 board
+   * 3.3v (pin 36) -> VCC on MPU9250 board
+   * GND (pin 38)  -> GND on MPU9250 board
+
+The example here uses SPI port 0. Power is supplied from the 3.3V pin.
+
+[NOTE]
+======
+There are many different manufacturers who sell boards with the MPU9250. Whilst they all appear slightly different, they all have, at least, the same 6 pins required to power and communicate. When wiring up a board that is different to the one in the diagram, ensure you connect up as described in the previous paragraph.
+======
+
+
+[[mpu9250_spi_wiring]]
+[pdfwidth=75%]
+.Wiring Diagram for MPU9250.
+image::mpu9250_spi_bb.png[]
+
+== List of Files
+
+CMakeLists.txt:: CMake file to incorporate the example in to the examples build tree.
+mpu9250_spi.c:: The example code.
+
+== Bill of Materials
+
+.A list of materials required for the example
+[[MPU9250-bom-table]]
+[cols=3]
+|===
+| *Item* | *Quantity* | Details
+| Breadboard | 1 | generic part
+| Raspberry Pi Pico | 1 | http://raspberrypi.org/
+| MPU9250 board| 1 | generic part
+| M/M Jumper wires | 6 | generic part
+|===
+
+

spi/mpu9250_spi/mpu9250_spi.c

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+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include "pico/stdlib.h"
+#include "hardware/spi.h"
+
+/* Example code to talk to a MPU9250 MEMS accelerometer and gyroscope.
+   Ignores the magnetometer, that is left as a exercise for the reader.
+
+   This is taking to simple approach of simply reading registers. It's perfectly
+   possible to link up an interrupt line and set things up to read from the
+   inbuilt FIFO to make it more useful.
+
+   NOTE: Ensure the device is capable of being driven at 3.3v NOT 5v. The Pico
+   GPIO (and therefor SPI) cannot be used at 5v.
+
+   You will need to use a level shifter on the I2C lines if you want to run the
+   board at 5v.
+
+   Connections on Raspberry Pi Pico board and a generic MPU9250 board, other
+   boards may vary.
+
+   GPIO 4 (pin 6) MISO/spi0_rx-> ADO on MPU9250 board
+   GPIO 5 (pin 7) Chip select -> NCS on MPU9250 board
+   GPIO 6 (pin 9) SCK/spi0_sclk -> SCL on MPU9250 board
+   GPIO 7 (pin 10) MOSI/spi0_tx -> SDA on MPU9250 board
+   3.3v (pin 36) -> VCC on MPU9250 board
+   GND (pin 38)  -> GND on MPU9250 board
+
+   Note: SPI devices can have a number of different naming schemes for pins. See
+   the Wikipedia page at https://en.wikipedia.org/wiki/Serial_Peripheral_Interface
+   for variations.
+   The particular device used here uses the same pins for I2C and SPI, hence the
+   using of I2C names
+*/
+
+#define PIN_MISO 4
+#define PIN_CS   5
+#define PIN_SCK  6
+#define PIN_MOSI 7
+
+#define SPI_PORT spi0
+#define READ_BIT 0x80
+
+static inline void cs_select() {
+    asm volatile("nop \n nop \n nop");
+    gpio_put(PIN_CS, 0);  // Active low
+    asm volatile("nop \n nop \n nop");
+}
+
+static inline void cs_deselect() {
+    asm volatile("nop \n nop \n nop");
+    gpio_put(PIN_CS, 1);
+    asm volatile("nop \n nop \n nop");
+}
+
+static void mpu9250_reset() {
+    // Two byte reset. First byte register, second byte data
+    // There are a load more options to set up the device in different ways that could be added here
+    uint8_t buf[] = {0x6B, 0x00};
+    cs_select();
+    spi_write_blocking(SPI_PORT, buf, 2);
+    cs_deselect();
+}
+
+
+static void read_registers(uint8_t reg, uint8_t *buf, uint16_t len) {
+    // For this particular device, we send the device the register we want to read
+    // first, then subsequently read from the device. The register is auto incrementing
+    // so we don't need to keep sending the register we want, just the first.
+
+    reg |= READ_BIT;
+    cs_select();
+    spi_write_blocking(SPI_PORT, &reg, 1);
+    sleep_ms(10);
+    spi_read_blocking(SPI_PORT, 0, buf, len);
+    cs_deselect();
+    sleep_ms(10);
+}
+
+
+static void mpu9250_read_raw(int16_t accel[3], int16_t gyro[3], int16_t *temp) {
+    uint8_t buffer[6];
+
+    // Start reading acceleration registers from register 0x3B for 6 bytes
+    read_registers(0x3B, buffer, 6);
+
+    for (int i = 0; i < 3; i++) {
+        accel[i] = (buffer[i * 2] << 8 | buffer[(i * 2) + 1]);
+    }
+
+    // Now gyro data from reg 0x43 for 6 bytes
+    read_registers(0x43, buffer, 6);
+
+    for (int i = 0; i < 3; i++) {
+        gyro[i] = (buffer[i * 2] << 8 | buffer[(i * 2) + 1]);;
+    }
+
+    // Now temperature from reg 0x41 for 2 bytes
+    read_registers(0x41, buffer, 2);
+
+    *temp = buffer[0] << 8 | buffer[1];
+}
+
+int main() {
+    stdio_init_all();
+
+    printf("Hello, MPU9250! Reading raw data from registers via SPI...\n");
+
+    // This example will use SPI0 at 0.5MHz.
+    spi_init(SPI_PORT, 500 * 1000);
+    gpio_set_function(PIN_MISO, GPIO_FUNC_SPI);
+    gpio_set_function(PIN_SCK, GPIO_FUNC_SPI);
+    gpio_set_function(PIN_MOSI, GPIO_FUNC_SPI);
+
+    // Chip select is active-low, so we'll initialise it to a driven-high state
+    gpio_init(PIN_CS);
+    gpio_set_dir(PIN_CS, GPIO_OUT);
+    gpio_put(PIN_CS, 1);
+
+    mpu9250_reset();
+
+    // See if SPI is working - interrograte the device for its I2C ID number, should be 0x71
+    uint8_t id;
+    read_registers(0x75, &id, 1);
+    printf("I2C address is 0x%x\n", id);
+
+    int16_t acceleration[3], gyro[3], temp;
+
+    while (1) {
+        mpu9250_read_raw(acceleration, gyro, &temp);
+
+        // These are the raw numbers from the chip, so will need tweaking to be really useful.
+        // See the datasheet for more information
+        printf("Acc. X = %d, Y = %d, Z = %d\n", acceleration[0], acceleration[1], acceleration[2]);
+        printf("Gyro. X = %d, Y = %d, Z = %d\n", gyro[0], gyro[1], gyro[2]);
+        // Temperature is simple so use the datasheet calculation to get deg C.
+        // Note this is chip temperature.
+        printf("Temp. = %f\n", (temp / 340.0) + 36.53);
+
+        sleep_ms(100);
+    }
+
+    return 0;
+}