MCU LOAD

dsPIC30F dsPIC33F dsPIC33E dsPIC33C dsPIC33A PIC32

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The MCU LOAD block measures CPU utilization using a hardware timer and optionally toggles a GPIO pin for external measurement.

When to use:

When to use:

• Need runtime CPU load monitoring (display on HMI, log to memory)
• Profiling application to find optimization opportunities
• Verifying system has sufficient CPU margin before production
• External measurement needed (oscilloscope/logic analyzer on GPIO pin)
• Tuning scheduler overload thresholds based on actual load

When NOT to use:

• No runtime interest in CPU utilization (use compile-time analysis instead)
• Timer resource is limited — block consumes one hardware timer
• GPIO pin conflicts with peripheral — disable pin output if not needed
• Minimal overhead required — block adds small measurement overhead

Overview

The MCU LOAD block provides CPU load measurement using a dedicated hardware timer. The timer runs only when the MCU is not idle, accumulating busy time.

Key features:

• Hardware timer-based measurement (minimal overhead)
• Optional GPIO pin toggle for oscilloscope/logic analyzer measurement
• Output port provides load value
• Automatic timer resource allocation

Block Dialog

Ports

Outputs

Parameters

Measurement Method

The block uses a hardware timer that increments only when the MCU is busy (not idle). The timer value represents accumulated busy time within the measurement window.

Timer behavior:

• Timer runs when executing tasks or ISRs
• Timer stops when MCU enters idle loop
• Timer value read at block sample time
• Result stored in MCHP_MCULoadResult[] array (multitasking) or reset after read (single-tasking)

GPIO pin (optional):

• Pin set high when CPU is busy
• Pin set low during idle
• Allows external measurement with oscilloscope/logic analyzer

Timer Resource Allocation

The block automatically allocates a hardware timer with these characteristics:

• Timer Type: 5 (MCU Load exclusive use)
• Timer Startup: 0 (Timer off, PR = default 65535)
• Prescaler: Selectable based on device family

Prescaler Options by Device Family

The callback calculates timer resolution based on:

Ticks = PRESCALER / FcyRef
Resolution = Ticks (per tick)
MaxPeriod = Ticks * 65536 (max measurement window)

Code Generation

TLC Implementation:

• Block type: MCHP_MCU_LOAD
• Timer initialization: Timer value set to 0 at startup (dsPIC33A/PIC32A only)
• Output: Reads MCHP_MCULoadResult[idx] for corresponding TID and Timer
• Multitasking: Result persists until next read
• Single-tasking: Result reset to 0 after each read

Generated variables:

extern volatile uint16_t MCHP_MCULoadResult[];           // Load result per TID
extern volatile uint16_t MCHP_MCULoadPreviousTimerValue[]; // Previous timer value
extern volatile unsigned int mcuFlagRecursion;           // Recursion protection flag

RTWdata fields:

• MCULoadTimerRef: Allocated timer index
• MCULoadPin: GPIO pin index (-1 if not used)

Parameter Visibility

The “Output mcu load measurement” checkbox controls visibility of:

• TIMER_Resolution (visible when ON)
• Info (visible when ON)
• SampleTime (visible when ON)

When unchecked, the output port is removed and timer still runs but result is not output.

Internal Parameters

Hidden parameters managed by callback:

• MCULoadPin_TXT: Stores pin selection text (e.g., “A0 / Pin[17]”)
• TIMER_Resolution_TXT: Stores resolution text (e.g., “Resol: 0.1143(us) - Max: 7.49(ms)”)
• MCHP_PORT: Pin configuration string {MCU Load Pin}{MCU_Load}0:1:PortPin;
• MCHP_TIMER_REQUEST: Timer allocation request string
• MCHP_TIMER_RESULT: Timer allocation result (timer index and period)

Related Blocks

• Tasks State - Task execution monitoring
• Scheduler Options - Scheduler configuration