FlexTimer peripheral of NXP S32K1xx MCU( S32K144 MCU and ElecronicsV3 Board)

About FlexTimer Peripheral of S32K144 MCU:

What is FlexTIMER Peripheral?

FlexTimer is a peripheral present in NXP S32K1xx MCU’s, which is used for input capture, output capture, generation of PWM signals and time delays. We are going to focus on PWM signals part and usecase of FTM Peripheral for generating PWM signals.

As FTM is a peripheral of MCU, so it has intances and with each instance certain number of MCU pins which are referred as channels. In S32K144 their are 4 instances of FTM and each instance has 8 channels. Instances are abrievted as FTM0, FTM1, FTM2 and FTM3. Each Instance has its own Peripheral registers where the configuration of those instances is done.  Their are number of registers, in FTM peripheral through which its configuration for different features is done and we also get status. We are not going to dive into every register, will mention important registers, as in industry register level coding is not implemented but understanding of registers is what is important. Each Instance has 8 channels, which are reffered as CH0-CH7. So naming convection goes like this:

Table showing FTM Instance and Then FTM Channels of that sinstance and all MCU pins which can be used for that channel.

For PWM,  FTM Peripheral has following functnalities and features

• PWM Signal Type: Center Aligned and Edge Aligned PWM Signals:
• Combine Mode PWM signals in inverted/duplicate
• PWM Interrupts: Every channel has interrupt source. Interrupt can be generated on counter match or counter overflow.
• Detection of rising and failing edges of PWM signals: We can configure interrupt generation when counter matches or overflows based on the polaruty of PWM signal.
• Hardware-Software Trigger: Generation of PWM signals and variation of PWM parameters at the detection of some hardware specific events. Lets say we want to generate PWM pulse only when some ADC readings are taken. So we can configure PWM signal to generate when ADC hardware conversion si done.
• Fault control and synchronization points. 

How FTM peripheral works is,

For understanding the ftm peripheral features and functionalities we will understand them via storytelling!!! Story telling in terms of what steps have to be followed to use ftm peripheral and correspondingly covering its different features.

1. We configure the clock values for ftm peripheral, that is whether the ftm peripheral is going to get clock from system clock, fixed clock or external clock and  also configures the prescaler values, to divide the ftm clock if needed. FTM CLOCK CONFIGURATION IS IMPORTANT step as based on this only, parameters of pwm signals are calculated. Their are 3 inputs of clocks for FTM peripheral: either system clock, or crystal oscillator clock( that is fixed clock) or some external clock ( connected to some pin of MCU).
2. After that we configure in which mode FTM peripheral has to be used, whether input capture mode, output capture mode. Output capture mode is what we are going to use. Output capture mode means outputings some digital signals. And Input capture mode means inputting some digital signals.
3. After output capture mode,  which type of pwm signal. These settings are done by setting the values of highlighted bits according to following table. These bits are part of these registers. Based on the mode of ftm peripheral, ftm peripheral will work. As in this module we are learning and focusing on pwm signals, so we highlighted sections of table is what is going to be of our concern.   
   1. Edge Aligned Mode
   2. Center Aligned Mode
   3. Combine Mode(Complementary)

• Each Instance has 8 channels, so every channel has its own peripheral registers by the name of CnSC. In CnSC register this pwm mode of configuration is done. 

1. After that, we configure the values into counters of FTM. As stated Timer peripheral has 3 counters in it. MAX counter, Variable counter and Threshold counter. In FTM peripheral MAX counter is MOD peripheral register. Value put on this register determines the frequency /period of pwm signal. Variable register is COUNT peripheral register. This counter starts incrementing from 0 once ftm peripheral is enabled or triggered. Threshol Counter we will touch in couple of mins after.
   • For each channel their is register CnV. This register act as Threshold counter for pwm signal coming from corresponding channel or we can say pin of mcu. Value put on this register will determine the duty cycle of the signal as when COUNT counter matches the value of this register, pwm signal state changes according to configured polarity.
2. Now polarity of pwm channel will determine, whether pwm signal would have high to low transition or low to high transition on counter match. The polarity configuration is important as this will determine the duty cycle parameter. So there are 2 things in polarity, state of pwm signal before counter match and state of pwm signal after counter match. Based on polarity configuration, rising or failing edges would be generated on counter match and counter overflows.
3. 6) Another important thing is updates of counter registers and pwm polarity. You see, counter registers like MOD, CnV and COUNT very much control the PWM signal parameters and PWM polarity register bits control the logic levels of pwm signal. Ftm peripheral has feature to configure when these register values should be updated, that is either on software trigger means software will write the Data on the registers and it would be loaded into them. Or hardware trigger that on detection of sone external signal, the values of these registers would be changed. This updation of register is also called as Reload point of counter registers and values in FTM peripheral.
4. If we are using interrupts then interrupt configuration is also done for each indiviual channel for different events. By events we mean counter match or counter overfflow. For every channels of FTM Instance their are bits in x register, If we set these bits then interrupt functionaly would be on for those Channels. When Counter match happens then channel interrupt handlers are fired and when counter oveflow happens then overflow interrupt handler is fired. Overflow interrupt handler is comman for all channels, but counter match handlers is individual for channels.

Apart from these, their are 2 more features in ftm peripheral for pwm signals that is fault control and synchronization points. Those are advance topics that we will cover un next version of these courses.

FTM Peripheral important peripheral registers for PWM

Formula Calculation of Frequency/Duty Cycle and Timeperiod for PWM Signals via FTM Peripheral