Zoltan Hudak
mbed API for Raspberry Pi boards.
mbedPi
This is an attempt to implement a limited number of mbed APIs for Raspberry Pi single-board computers. The project was inspired by and based on the arduPi library developed for the Arduino by Cooking Hacks .
Specifications
- Chip: Broadcom BCM2836 SoC
- Core architecture: Quad-core ARM Cortex-A7
- CPU frequency: 900 MHz
- GPU: Dual Core VideoCore IV® Multimedia Co-Processor
- Memory: 1GB LPDDR2
- Operating System: Boots from Micro SD card, running a version of the Linux operating system
- Power: Micro USB socket 5V, 2A
Connectors
- Ethernet: 10/100 BaseT Ethernet socket
- Video Output: HDMI (rev 1.3 & 1.4)
- Audio Output: 3.5mm jack, HDMI
- USB: 4 x USB 2.0 Connector
- GPIO Connector: 40-pin 2.54 mm (100 mil) expansion header: 2x20 strip providing 27 GPIO pins as well as +3.3 V, +5 V and GND supply lines
- Camera Connector: 15-pin MIPI Camera Serial Interface (CSI-2)
- JTAG: Not populated
- Display Connector: Display Serial Interface (DSI) 15 way flat flex cable connector with two data lanes and a clock lane
- Memory Card Slot: Micro SDIO
GPIO connector pinout
Information
Only the labels printed in blue/white or green/white (i.e. p3, gpio2 ...) must be used in your code. The other labels are given as information (alternate-functions, power pins, ...).
Building programs for the Raspberry Pi with mbedPi
I use Qt Creator for development, however you can use any other IDE available on the Raspberry Pi (e.g. Geany) if you like. For a quick try:
- Install Qt and the Qt Creator onto your Raspberry Pi. Then create a new "Blinky" Plain non-Qt C++ Project as follows:
- Change the main code as below:
main.cpp
#include "mbedPi.h"
int main()
{
DigitalOut myled(p7);
while(1) {
myled = 1; // LED is ON
wait(0.2); // 200 ms
myled = 0; // LED is OFF
wait(1.0); // 1 sec
printf("Blink\r\n");
}
}
- Copy the mbedPi.zip file into your project's folder and unzip.
- Add the mbedPi.h and mbedPi.cpp files to your project by right clicking on the "Blinky" project and then clicking on the "Add Existing Files..." option in the local menu:
- Double click on Blinky.pro to open it for editing and add new libraries by inserting a new line as follows:
- Compile the project.
- Connect an LED through a 1k resistor to pin 7 and the ground on the Raspberry Pi GPIO connector.
- Run the binary as sudo (sudo ./Blinky) and you should see the LED blinking.
- Press Ctrl+c to stop running the application.
Diff: include/PwmOut.h
- Revision:
- 1:1f2d9982fa8c
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/PwmOut.h Tue Dec 20 12:08:07 2022 +0000
@@ -0,0 +1,93 @@
+#ifndef _PWM_OUT_H_
+#define _PWM_OUT_H_
+
+#include "BCM2835.h"
+
+class PwmOut {
+
+public:
+
+ /** Create a PwmOut connected to the specified pin
+ *
+ * @param pin PwmOut pin to connect to
+ */
+ PwmOut(PinName pin = gpio18);
+
+ ~PwmOut();
+
+ /** Set the output duty-cycle, specified as a percentage (float)
+ *
+ * @param value A floating-point value representing the output duty-cycle,
+ * specified as a percentage. The value should lie between
+ * 0.0f (representing on 0%) and 1.0f (representing on 100%).
+ * Values outside this range will be saturated to 0.0f or 1.0f.
+ */
+ void write(float value);
+
+ /** Return the current output duty-cycle setting, measured as a percentage (float)
+ *
+ * @returns
+ * A floating-point value representing the current duty-cycle being output on the pin,
+ * measured as a percentage. The returned value will lie between
+ * 0.0f (representing on 0%) and 1.0f (representing on 100%).
+ *
+ * @note
+ * This value may not match exactly the value set by a previous write().
+ */
+ float read();
+
+ /** Set the PWM period, specified in bcm2835PWMPulseWidth (micro/nano seconds), keeping the duty cycle the same.
+ * @note Sets clock divider according to the required period.
+ * @param period Change the period of a PWM signal. The allowed values are:
+ * BCM2835_PWM_PERIOD_212_US -> 213.33 us = 4.6875 kHz
+ * BCM2835_PWM_PERIOD_107_US -> 106.66 us = 9.375 kHz
+ * BCM2835_PWM_PERIOD_53_US -> 53.33 us = 18.75 kHz
+ * BCM2835_PWM_PERIOD_27_US -> 26.66 us = 37.50 kHz
+ * BCM2835_PWM_PERIOD_13_US -> 13.33 us = 75.00 kHz
+ * BCM2835_PWM_PERIOD_7_US -> 6.66 us = 150.00 kHz
+ * BCM2835_PWM_PERIOD_3_US -> 3.33 us = 300.00 kHz
+ * BCM2835_PWM_PERIOD_2_US -> 1.66 us = 600.00 kHz
+ * BCM2835_PWM_PERIOD_833_NS -> 833.33 ns = 1200.00 kHz
+ * BCM2835_PWM_PERIOD_417_NS -> 416.66 ns = 2400.00 kHz
+ * BCM2835_PWM_PERIOD_208_NS -> 208.33 ns = 4800.00 kHz
+ * BCM2835_PWM_PERIOD_104_NS -> 104.16 ns = 9600.00 kHz
+ */
+ void period_ms(int period);
+ void period_us(int period);
+ void period_ns(int period);
+
+ /** A operator shorthand for write()
+ * \sa PwmOut::write()
+ */
+ PwmOut &operator= (float value)
+ {
+ write(value);
+ return *this;
+ }
+
+ /** A operator shorthand for write()
+ * \sa PwmOut::write()
+ */
+ PwmOut &operator= (PwmOut &rhs)
+ {
+ write(rhs.read());
+ return *this;
+ }
+
+ /** An operator shorthand for read()
+ * \sa PwmOut::read()
+ */
+ operator float()
+ {
+ return read();
+ }
+
+protected:
+ PinName _pwmPin;
+ float _duty_cycle;
+ uint32_t _range;
+ uint32_t _period;
+};
+
+#endif // _PWM_OUT_H_
+