SAM3X8E / Arduino Due: Timer/Counter not generating PWM on TIOB0 (PB27) — output stuck HIGH

I'm trying to generate a PWM signal on PB27 / Arduino Due pin 13, which corresponds to TIOB0 on the SAM3X8E (used on the Arduino Due).

However, the output pin just goes HIGH and stays there — no PWM signal appears on the scope. Interrupts are not an option, so I’m trying to use the Timer Counter peripheral directly.

Here’s my minimal code:

// === PB27 / Arduino Pin 13 = TIOB0 ===
        pmc_set_writeprotect(false);
        pmc_enable_periph_clk(ID_TC0);

        PIOB->PIO_PDR = PIO_PB27;    // Disable GPIO
        PIOB->PIO_ABSR &= ~PIO_PB27; // Peripheral A für TIOB0

        TC_Configure(TC0, 0,
            TC_CMR_WAVE |                  // Waveform mode
            TC_CMR_WAVSEL_UP_RC |          // Count up to RC
            TC_CMR_ACPA_CLEAR |            // Clear on RA
            TC_CMR_ACPC_SET |              // Set on RC
            TC_CMR_TCCLKS_TIMER_CLOCK4);


        TC_SetRA(TC0, 0, rc / 2);
        TC_SetRC(TC0, 0, rc);
        TC_Start(TC0, 0);

        delay(duration);

        TC_Stop(TC0, 0);
        PIOB->PIO_PER = PIO_PB27;   // Enable GPIO
        PIOB->PIO_OER = PIO_PB27;   // Output enable
        PIOB->PIO_CODR = PIO_PB27;  // Set LOW

        return true;

I’ve verified that rc has a valid value, and the peripheral clock is enabled for ID_TC0. Still, PB27 remains stuck HIGH — no PWM transitions occur.

I’m not using any interrupts or Arduino libraries (just direct register access). What am I missing in the Timer Counter configuration to actually get a waveform on TIOB0?

Environment:

• Arduino Due (Atmel SAM3X8E)
• VS Code/ PlatformIO/ direct register access
• No interrupts used