
General-purpose timers (TIM16/TIM17)
RM0453
920/1454
RM0453 Rev 2
Particular case: OCx fast enable
In One-pulse mode, the edge detection on TIx input set the CEN bit which enables the
counter. Then the comparison between the counter and the compare value makes the
output toggle. But several clock cycles are needed for these operations and it limits the
minimum delay t
DELAY
min we can get.
If one wants to output a waveform with the minimum delay, the OCxFE bit can be set in the
TIMx_CCMRx register. Then OCxRef (and OCx) are forced in response to the stimulus,
without taking in account the comparison. Its new level is the same as if a compare match
had occurred. OCxFE acts only if the channel is configured in PWM1 or PWM2 mode.
27.3.14 UIF bit remapping
The IUFREMAP bit in the TIMx_CR1 register forces a continuous copy of the Update
Interrupt Flag UIF into bit 31 of the timer counter register (TIMxCNT[31]). This allows both
the counter value and a potential roll-over condition signaled by the UIFCPY flag, to be
atomically read. In particular cases, it can ease the calculations by avoiding race conditions
caused for instance by a processing shared between a background task (counter reading)
and an interrupt (Update Interrupt).
There is no latency between the assertions of the UIF and UIFCPY flags.
27.3.15 Slave mode – combined reset + trigger mode
In this case, a rising edge of the selected trigger input (TRGI) reinitializes the counter,
generates an update of the registers, and starts the counter.
This mode is used for one-pulse mode.
27.3.16 DMA burst mode
The TIMx timers have the capability to generate multiple DMA requests on a single event.
The main purpose is to be able to re-program several timer registers multiple times without
software overhead, but it can also be used to read several registers in a row, at regular
intervals.
The DMA controller destination is unique and must point to the virtual register TIMx_DMAR.
On a given timer event, the timer launches a sequence of DMA requests (burst). Each write
into the TIMx_DMAR register is actually redirected to one of the timer registers.
The DBL[4:0] bits in the TIMx_DCR register set the DMA burst length. The timer recognizes
a burst transfer when a read or a write access is done to the TIMx_DMAR address), i.e. the
number of transfers (either in half-words or in bytes).
The DBA[4:0] bits in the TIMx_DCR registers define the DMA base address for DMA
transfers (when read/write access are done through the TIMx_DMAR address). DBA is
defined as an offset starting from the address of the TIMx_CR1 register.
Example:
00000: TIMx_CR1,
00001: TIMx_CR2,
00010: TIMx_SMCR,