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49 lines
2.4 KiB
ReStructuredText
49 lines
2.4 KiB
ReStructuredText
DATA STRUCT
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===========
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The struct serves as the data payload for sending control signals from transmitting device to the receiver using ESP-NOW.
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In addition, it may contain additional data such as telemetry, battery status, etc.
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The *sensors_data_t* struct is designed as a data payload that encapsulates all control commands and sensor states relevant to the vehicle's operation.
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It's intended to be sent from a transmitting device (like a remote control or master controller) to a receiver (such as a microcontroller onboard the vehicle).
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.. code-block:: c
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typedef struct {
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int x_axis; // Joystick x-position
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int y_axis; // Joystick y-position
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bool nav_bttn; // Joystick push button
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bool led; // LED ON/OFF state
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uint8_t motor1_rpm_pwm; // PWMs for 4 DC motors
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uint8_t motor2_rpm_pwm;
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uint8_t motor3_rpm_pwm;
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uint8_t motor4_rpm_pwm;
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} __attribute__((packed)) sensors_data_t;
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When used with communication protocols like ESP-NOW, this struct is **encoded** into a byte stream, then
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**transmitted** at regular intervals or in response to user input, and finally
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**decoded** on the receiving end to control hardware.
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Data Payload
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------------
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*x_axis* and *y_axis* fields capture analog input from a joystick, determining direction and speed.
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*nav_bttn* represents a joystick push-button.
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*led* allows the transmitter to toggle an onboard LED and is used for status indication (e.g. pairing, battery warning, etc).
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*motor1_rpm_pwm* to *motor4_rpm_pwm* provide individual PWM signals to four DC motors.
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This enables fine-grained speed control, supports differential drive configurations, and even allows for maneuvering in multi-directional platforms like omni-wheel robots.
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Why use __attribute((packed))?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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ESP-NOW uses fixed-size data packets (up to 250 bytes). The *__attribute__((packed))* removes compiler-added padding for precise byte alignment.
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As *packed* attribute tells the compiler not to add any padding between fields in memory, this makes the struct:
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- Compact
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- Predictable for serialization over protocols like UART or ESP-NOW
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- Ideal for low-latency transmission in embedded systems
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This ensures the receiver interprets the exact byte layout you expect, minimizing bandwidth and maximizing compatibility across platforms. |