High-resolution timer (HRTIM) RM0440
924/2126 RM0440 Rev 4
When BMPREN bits is reset, the write access into BMCMPR and BMPER directly updates
the active register. In this case, it is necessary to consider when the update is done during
the overall burst period, for the 2 cases below:
a) Compare register update
If the new compare value is above the current burst mode counter value, the new compare
is taken into account in the current period.
If the new compare value is below the current burst mode counter value, the new compare
is taken into account in the next burst period in continuous mode, and ignored in single-shot
mode (no compare match occurs and the idle state lasts until the end of the idle period).
b) Period register update
If the new period value is above the current burst mode counter value, the change is taken
into account in the current period.
Note: If the new period value is below the current burst mode counter value, the new period is not
taken into account, the burst mode counter overflows (at 0xFFFF) and the change is
effective in the next period. In single-shot mode, the counter rolls over at 0xFFFF and the
burst mode re-starts for another period up to the new programmed value.
Burst mode emulation using a compound register
The burst mode controller only controls one or a set of timers for a single converter. When
the burst mode is necessary for multiple independent timers, it is possible to emulate a
simple burst mode controller using the DMA and the HRTIM_CMP1CxR compound register,
which holds aliases of both the repetition and the compare 1 registers.
This is applicable to a converter which only requires a simple PWM (typically a buck
converter), where the duty cycle only needs to be updated. In this case, the CMP1 register
is used to reset the output (and define the duty cycle), while it is set on the period event.
In this case, a single 32-bit write access in CMP1CxR is sufficient to define the duty cycle
(with the CMP1 value) and the number of periods during which this duty cycle is maintained
(with the repetition value). To implement a burst mode, it is then only necessary to transfer
by DMA (upon repetition event) two 32-bit data in continuous mode, organized as follows:
CMPC1xR = {REP_Run; CMP1 = Duty_Cycle}, {REP_Idle; CMP1 = 0}
For instance, the values:
{0x0003 0000}: CMP1 = 0 for 3 periods
{0x0001 0800}: CMP1 = 0x0800 for 1 period
provide a burst mode with 2 periods active every 6 PWM periods, as shown on Figure 241.
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