TMS320F280039: The problem of period calculation in HRPWM

TBPRDHR Calculation in TIDM-02013 Explained

The large pwmPeriod_ticks value is intentional — it's a fixed-point arithmetic technique that packs both the integer period (TBPRD) and the fractional high-resolution period (TBPRDHR) into a single 32-bit value.

How the Calculation Works

From your screenshot of CLLLC_HAL_setupHRPWMinUpDownCountModeWithDeadBand, the formula is:

pwmPeriod_ticks = (systemClock × 65536) / pwmFrequency / 2

With your parameters (120 MHz clock, 500.8 kHz resonant frequency, up-down count mode):

pwmPeriod_ticks = (120,000,000 × 65536) / 500,800 / 2 ≈ 7,864,729

This result is a 32-bit fixed-point number where:

• Upper 16 bits = integer period → loaded into TBPRD (the coarse clock ticks)
• Lower 16 bits = fractional period → loaded into TBPRDHR (the high-resolution MEP steps)

The division by 2 accounts for up-down count mode, where the PWM period equals 2×TBPRD 1.

The code then masks with 0xFFFFFF00 and writes directly to the TBPRDHR address using HWREG, which simultaneously sets both TBPRD (upper 16 bits) and TBPRDHR (lower 16 bits, high byte) in one 32-bit write 1.

Why Multiply by 65536?

The multiplication by 2^16 shifts the integer portion into the upper half-word while preserving the fractional portion in the lower half-word. When auto-conversion is enabled (HRCNFG[AUTOCONV]=1), the hardware uses the HRMSTEP register (written by the SFO calibration function) to automatically scale the fractional value in TBPRDHR into the correct number of MEP steps (~150 ps resolution per step) 2.

Recommended HRPWM Reference Materials

1. TMS320F280039 Technical Reference Manual — HRPWM Section (Section 20.15): Covers MEP operation, register descriptions, and worked examples of TBPRDHR/CMPAHR calculations with auto-conversion 1

2. SFO Library Documentation (Section 20.15.2): Explains the Scale Factor Optimizer calibration that keeps HRMSTEP updated at runtime 1

3. C2000Ware SDK HRPWM Examples: The hrpwm_ex3_prd_updown_sfo.c example demonstrates high-resolution period control in up-down mode — directly relevant to your TIDM-02013 code 3

4. E2E FAQ on ePWM/HRPWM: A curated list of common questions and answers 4

Follow up: Are you planning to modify the resonant frequency dynamically at runtime, or are you primarily trying to understand the existing TIDM-02013 code before adapting it to your own CLLLC design?

1. TMS320F280039 Technical Reference Manual - HRPWM
2. TMS320F280039 Datasheet - HRPWM Electrical Data
3. E2E: HRPWM Period Accuracy in Up Count Mode
4. E2E FAQ: C2000 ePWM and HRPWM

Thanks

Srikanth