Datasheet

SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
990
Method 3: Automatic write of duty-cycle values and automatic trigger of the update
In this mode, the update of the duty cycle values is made automatically by the Peripheral DMA Controller (PDC).
The update of the period value, the dead-time values and the update period value must be done by writing in their
respective update registers with the CPU (respectively PWM_CPRDUPDx, PWM_DTUPDx and
PWM_SCUPUPD).
To trigger the update of the period value and the dead-time values, the user must use the bit UPDULOCK which
allows to update synchronously (at the same PWM period) the synchronous channels:
 If the bit UPDULOCK is set to 1, the update is done at the next PWM period of the synchronous channels.
 If the UPDULOCK bit is not set to 1, the update is locked and cannot be performed.
After writing the UPDULOCK bit to 1, it is held at this value until the update occurs, then it is read 0.
The update of the duty-cycle values and the update period value is triggered automatically after an update period.
To configure the automatic update, the user must define a value for the Update Period by the field UPR in the
“PWM Sync Channels Update Period Register” (PWM_SCUP). The PWM controller waits UPR+1 periods of
synchronous channels before updating automatically the duty values and the update period value.
Using the PDC removes processor overhead by reducing its intervention during the transfer. This significantly
reduces the number of clock cycles required for a data transfer, which improves microcontroller performance.
The PDC must write the duty-cycle values in the synchronous channels index order. For example if the channels 0,
1 and 3 are synchronous channels, the PDC must write the duty-cycle of the channel 0 first, then the duty-cycle of
the channel 1, and finally the duty-cycle of the channel 3.
The status of the PDC transfer is reported in the “PWM Interrupt Status Register 2” (PWM_ISR2) by the following
flags:
 WRDY: this flag is set to 1 when the PWM Controller is ready to receive new duty-cycle values and a new
update period value. It is reset to 0 when the PWM_ISR2 register is read. The user can choose to
synchronize the WRDY flag and the PDC transfer request with a comparison match (see Section 38.6.3
“PWM Comparison Units”), by the fields PTRM and PTRCS in the PWM_SCM register.
 ENDTX: this flag is set to 1 when a PDC transfer is completed
 TXBUFE: this flag is set to 1 when the PDC buffer is empty (no pending PDC transfers)
 UNRE: this flag is set to 1 when the update period defined by the UPR field has elapsed while the whole data
has not been written by the PDC. It is reset to 0 when the PWM_ISR2 register is read.
Depending on the interrupt mask in the PWM_IMR2 register, an interrupt can be generated by these flags.