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PIC18 PWM Driver (#21)
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‎.gitignore‎

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doc/_build
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unit_tests/low_pass_filter_test
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.DS_Store

‎doc/pwm_driver.rst‎

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PIC18 Software PWM Driver
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*************************
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PIC18 PWM Driver
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****************
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The driver provides PWM output functionality for PIC18F26K83 on one pin, with timer only. Pulse-width/duty-cycle can be adjusted when output is enabled. Timer 2 is used by this driver.
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The driver provides PWM output functionality for the PIC18F26K83 using the CCP (Capture/Compare/PWM) modules. It supports up to four PWM channels, each with configurable pin mapping. Timer 2 is utilized by this driver to manage PWM periods.
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Integration
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===========
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ROCKETLIB_PWM_PIN Macro
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-----------------------
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Set ``ROCKETLIB_PWM_PIN`` macro to the pin register name for output, e.g. ``LATC6``
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Pin Configuration
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-----------------
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.. c:macro:: CONCAT(a, b, c)
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ROCKETLIB_PWM_INVERT_POLARITY Macro
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-----------------------------------
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Set ``ROCKETLIB_PWM_INVERT_POLARITY`` macro to inverse output polarity
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Concatenates three tokens to dynamically form register names.
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Interrupt
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---------
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``void timer2_handle_interrupt(void)`` have to be called when having a timer 2 interrupt
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:param a: First part of the token.
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:param b: Second part of the token.
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:param c: Third part of the token.
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SoftPWM Controller Functions
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============================
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.. c:macro:: CCPR_L(module)
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Accesses the CCPR Low register for the specified module.
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:param module: CCP module number (1-4).
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.. c:macro:: CCPR_H(module)
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Accesses the CCPR High register for the specified module.
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:param module: CCP module number (1-4).
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.. c:macro:: CCP_CON(module)
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Accesses the CCPxCON control register for the specified module.
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:param module: CCP module number (1-4).
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.. c:macro:: GET_TRIS_REG(port)
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Retrieves the TRIS register for the specified port.
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:param port: Port letter (A, B, C).
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.. c:macro:: GET_PPS_REG(port, pin)
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Retrieves the PPS register address for the specified port and pin.
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:param port: Port letter (A, B, C).
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:param pin: Pin number (0-7).
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.. c:macro:: SET_TRIS_OUTPUT(port, pin)
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Sets the specified pin as output by modifying the TRIS register.
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:param port: Port letter (A, B, C).
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:param pin: Pin number (0-7).
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.. c:macro:: ASSIGN_PPS(port, pin, ccp_module)
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Assigns the CCP module to the specified PPS register to map the peripheral to the desired pin.
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:param port: Port letter (A, B, C).
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:param pin: Pin number (0-7).
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:param ccp_module: CCP module number (1-4).
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CCP Mode Configuration
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----------------------
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.. c:macro:: CONFIGURE_CCP_MODE(ccp_module, ccp_con)
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Configure the CCP module for PWM mode.
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:param ccp_module: CCP module number (1-4)
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:param ccp_con: CCPxCON register to configure
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Output Pin Configuration
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------------------------
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.. c:macro:: SET_PWM_OUTPUT_PIN(ccp_module, output_pin)
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Set the TRIS register for the output pin.
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:param ccp_module: CCP module number (1-4)
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:param output_pin: Output pin number
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Duty Cycle Configuration
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------------------------
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.. c:macro:: WRITE_DUTY_CYCLE(ccp_module, duty_cycle)
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Write the 10-bit duty cycle value to the appropriate CCPRxH:CCPRxL register pair.
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:param ccp_module: CCP module number (1-4)
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:param duty_cycle: 10-bit duty cycle value (0-1023)
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PWM Controller Functions
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========================
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PWM Pin Configuration Structure
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-------------------------------
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.. c:type:: pwm_pin_config_t
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Structure that holds the configuration details for a PWM pin.
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:param port: Port letter (A, B, C).
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:param pin: Pin number (0-7).
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:param pps_reg: PPS register value for this pin.
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Initialization
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--------------
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.. c:function:: void pwm_init(uint16_t period)
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.. c:function:: w_status_t pwm_init(uint8_t ccp_module, pwm_pin_config_t pin_config, uint16_t pwm_period)
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Initialize Software PWM
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Initializes PWM for the specified CCP module with the given pin configuration and PWM period.
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:param uint16_t period: period in increment of 10 us
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:param ccp_module: CCP module number (1-4).
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:param pin_config: PWM pin configuration structure containing port, pin, and PPS register values.
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:param pwm_period: PWM period value.
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:return: W_SUCCESS on successful initialization, otherwise an error code.
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Enable
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------
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.. c:function:: void pwm_enable(void)
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This function configures Timer 2, sets the PWM period, and enables the PWM output for the specified CCP module.
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Enable PWM Output
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PWM Operation
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=============
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Disable
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-------
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.. c:function:: void pwm_disable(void)
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.. c:function:: w_status_t pwm_update_duty_cycle(uint8_t ccp_module, uint16_t duty_cycle)
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Disable PWM Output
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Updates the duty cycle of the specified CCP module to the new value.
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Set Duty Cycle
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--------------
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.. c:function:: bool pwm_set_duty_cycle(uint16_t duty_cycle)
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:param ccp_module: CCP module number (1-4).
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:param duty_cycle: New duty cycle value (0-1023).
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:return: W_SUCCESS if successful, W_INVALID_PARAM if parameters are out of range.
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The duty cycle is a 10-bit value that determines the percentage of time the signal stays high. The lower 8 bits are written to CCPRxL, and the upper 2 bits are written to CCPRxH.
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Timer Configuration
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-------------------
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.. c:macro:: CONFIGURE_TIMER2(pwm_period)
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Configures Timer 2 to manage PWM periods. The prescaler and postscaler are set to 1:1.
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:param pwm_period: PWM period value to load into the PR2 register.
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Helper Functions
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================
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PPS Configuration
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-----------------
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.. c:function:: static w_status_t configure_pps(uint8_t ccp_module, pwm_pin_config_t pin_config)
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Set duty cycle
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Configures Peripheral Pin Select (PPS) for the specified pin and CCP module. This function is essential for routing the PWM signal to the correct output pin.
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:param uint16_t duty_cycle: Duty cycle in per-mille(1/1000)
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:return: success or not
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:retval true: success
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:retval false: failed
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:param ccp_module: CCP module number (1-4).
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:param pin_config: Structure containing port, pin, and PPS register values.
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:return: W_SUCCESS if successful, W_INVALID_PARAM if the module number is out of range.
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Set Pulse Width
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---------------
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.. c:function:: bool pwm_set_pulse_width(uint16_t pulse_width)
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Error Handling
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==============
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Set pulse width
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Error Codes
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-----------
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- **W_SUCCESS**: Operation completed successfully.
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- **W_INVALID_PARAM**: Parameter value is out of range. Typically returned if an invalid CCP module number or duty cycle value is provided.
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:param uint16_t pulse_width: pulse width in increment of 10 us
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:return: success or not
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:retval true: success
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:retval false: failed
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Practical Considerations
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========================
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- **Timer Usage**: Ensure Timer 2 is not shared with other peripherals to avoid conflicts in PWM generation.
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- **Prescaler and Postscaler**: The prescaler and postscaler are currently set to 1:1 for simplicity. These can be adjusted to modify the frequency of the PWM signal.
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- **Pin Mapping**: Correct pin mapping is critical for proper operation. Incorrect configuration can result in no output or conflicts with other peripherals.

‎include/pwm.h‎

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#ifndef ROCKETLIB_PWM_H
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#define ROCKETLIB_PWM_H
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#include "common.h"
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#include <stdint.h>
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/* PWM Initialization
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period: Period in 10us
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Note only 10ms period work for now(period=1000)
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*/
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void pwm_init(uint16_t period);
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// Structure to hold the configuration details for a PWM pin
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typedef struct {
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uint8_t port; // Port letter (A, B, C)
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uint8_t pin; // Pin number (0-7)
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uint8_t pps_reg; // PPS register value for this pin
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} pwm_pin_config_t;
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/* Set PWM Duty Cycle
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duty_cycle: Duty cycle in per-mille(1/1000)
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*/
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void pwm_set_duty_cycle(uint16_t duty_cycle);
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// Macro to concatenate tokens for register naming
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// This macro concatenates three tokens together, used for constructing register names dynamically
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#define CONCAT(a, b, c) a##b##c
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void pwm_enable(void);
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// Macro to get the CCPR Low register based on module number
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// This macro forms the register name for the low byte of the Compare/Capture/PWM register
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#define CCPR_L(module) CONCAT(CCPR, module, L)
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void pwm_disable(void);
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// Macro to get the CCPR High register based on module number
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// This macro forms the register name for the high byte of the Compare/Capture/PWM register
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#define CCPR_H(module) CONCAT(CCPR, module, H)
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#endif
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// Macro to get the CCPxCON register based on module number
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// This macro forms the register name for the control register of the specified CCP module
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#define CCP_CON(module) CONCAT(CCP, module, CON)
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// Macro to get the TRIS register based on port letter
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// TRIS registers control the direction of pins (input or output)
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// This macro dynamically constructs the TRIS register name for a given port
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#define GET_TRIS_REG(port) CONCAT(TRIS, port, A)
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// Macro to get the PPS register address based on port and pin
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// PPS (Peripheral Pin Select) allows mapping of peripherals to different pins
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// This macro forms the PPS register name for a given port and pin
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#define GET_PPS_REG(port, pin) CONCAT(R, port, pin##PPS)
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// Macro to set the TRIS register for a specific pin
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// This macro configures the specified pin as an output by clearing the corresponding bit in the
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// TRIS register
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#define SET_TRIS_OUTPUT(port, pin) (GET_TRIS_REG(port) &= ~(1 << (pin)))
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// Macro to assign the CCP module to the PPS register
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// This macro assigns the CCP module to a specific pin by writing to the PPS register
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#define ASSIGN_PPS(port, pin, ccp_module) (*GET_PPS_REG(port, pin) = (ccp_module))
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// Function prototypes
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w_status_t pwm_init(
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uint8_t ccp_module, pwm_pin_config_t pin_config, uint16_t pwm_period
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); // Initializes the PWM for a specific CCP module
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w_status_t pwm_update_duty_cycle(
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uint8_t ccp_module, uint16_t duty_cycle
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); // Updates the duty cycle of the specified CCP module
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#endif /* ROCKETLIB_PWM_H */

‎pic18f26k83/pwm.c‎

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#include "pwm.h"
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#include <xc.h>
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// Helper function to configure PPS registers using macros
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static w_status_t configure_pps(uint8_t ccp_module, pwm_pin_config_t pin_config) {
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volatile uint8_t *pps_reg;
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// Ensure the CCP module number is within valid range (1-4)
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if (ccp_module < 1 || ccp_module > 4) {
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return W_INVALID_PARAM; // Return error if the module number is out of range
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}
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// Set the pin as output to drive PWM signal
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// This macro modifies the TRIS register to set the specified pin as an output
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SET_TRIS_OUTPUT(pin_config.port, pin_config.pin);
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// Assign the CCP module to the corresponding PPS register
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// This macro sets up the peripheral pin select to link the CCP module to the desired pin
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ASSIGN_PPS(pin_config.port, pin_config.pin, ccp_module);
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return W_SUCCESS; // Return success status after configuring PPS
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}
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// Initialize PWM for a specific CCP module
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w_status_t pwm_init(uint8_t ccp_module, pwm_pin_config_t pin_config, uint16_t pwm_period) {
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// Configure PPS registers to map CCP module to the selected pin
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w_status_t status = configure_pps(ccp_module, pin_config);
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if (status != W_SUCCESS) {
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return status; // Return error status if PPS configuration fails
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}
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// Obtain the address of the CCPxCON register using macro
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volatile uint8_t *ccp_con = &CCP_CON(ccp_module);
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*ccp_con = 0x8C; // Enable CCP module in PWM mode (PWM mode selection)
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// Set PWM period using Timer2
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PR2 = pwm_period & 0xFF; // Load lower 8 bits of PWM period into PR2 register
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TMR2 = 0; // Reset Timer2 count to 0
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T2CONbits.T2CKPS = 0; // Set Timer2 prescaler to 1:1 (no prescaling)
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T2CONbits.TOUTPS = 0; // Set Timer2 postscaler to 1:1 (no postscaling)
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T2CONbits.TMR2ON = 1; // Start Timer2 to begin PWM operation
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// Wait for Timer2 to reach the period value before starting PWM
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while (!PIR1bits.TMR2IF) {} // Wait until Timer2 overflow flag is set
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PIR1bits.TMR2IF = 0; // Clear Timer2 interrupt flag to continue
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return W_SUCCESS; // Return success status after PWM initialization
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}
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// Update the duty cycle of a specific CCP module
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w_status_t pwm_update_duty_cycle(uint8_t ccp_module, uint16_t duty_cycle) {
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// Validate CCP module and duty cycle range
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if (ccp_module < 1 || ccp_module > 4 || duty_cycle > 1023) {
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return W_INVALID_PARAM; // Return error if module number or duty cycle is out of range
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}
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// Update the lower 8 bits of the duty cycle
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// This sets the low byte of the duty cycle for the PWM signal
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CCPR_L(ccp_module) = duty_cycle & 0xFF;
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// Update the upper 2 bits of the duty cycle for 10-bit resolution
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// This sets the high bits of the duty cycle to achieve 10-bit PWM precision
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CCPR_H(ccp_module) = (duty_cycle >> 8) & 0x03;
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return W_SUCCESS; // Return success status after updating duty cycle
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}

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