Texas Instruments TMS320C6201 Reference Manual page 143

6.7 Initiating an EDMA Transfer
6.7.1 Synchronization of EDMA Transfers
There are two ways to initiate data transfer using the EDMA. One is CPU-initi-
ated EDMA and the other is an event-triggered EDMA. The latter is a more typi-
cal usage of the EDMA. Each EDMA channel can be started independently.
The CPU can also disable an EDMA channel by disabling the event associated
with that channel.
CPU-initiated EDMA or unsynchronized EDMA: The CPU can write to
the event set register, ESR (described in section 6.3) in order to start an
EDMA transfer. Writing a '1' to the corresponding event in the ESR triggers
an EDMA event. Just as with a normal event, the transfer parameters in
the EDMA parameter RAM corresponding to this event are passed to the
address generation hardware, which performs the requested access of
the EMIF, L2 memory or peripherals, as appropriate. CPU-initiated EDMA
transfers are unsynchronized data transfers. The event's enable bit does
not have to be set in the EER for CPU-initiated EDMA transfers. This is
because a CPU write to the ESR is treated as a real-time event.
Event-triggered EDMA: As the name suggests, an event that is latched
in the event register, ER, via the event encoder (see section 6.4) causes
its transfer parameters to be passed on to the address generation hard-
ware, which performs the requested accesses. Although the event causes
this transfer, it is very important that the event itself be enabled by the CPU.
Writing a '1' to the corresponding bit in EER enables an event. Alternative-
ly, an event is still latched in the ER even if its corresponding enable bit in
EER is '0' (disabled). The EDMA transfer related to this event occurs as
soon as it is enabled in EER.
Synchronization allows EDMA transfers to be triggered by events either from
peripherals, interrupts from external devices, or an EDMA channel completion
event. The 16 EDMA channels can start a transfer depending on the type of
synchronization event associated with that channel. Table 6–4 shows the 16
events that initiate the 16 EDMA channels to start a transfer.
The association of an event to a channel is fixed. Unlike the existing
'C6201-type DMA, each of the 16 EDMA channels have one specific type of
event associated with it. For example, if bit 4 (event 4) in EER is set, then an
external interrupt on EXT_INT4 pin initiates a transfer on EDMA channel 4.
Initiating an EDMA Transfer
EDMA Controller 6-17