The REPEAT instruction is used to store the repeat count value into
the UPDI repeat counter register. When instructions are used with
REPEAT, protocol overhead for SYNCH- and Instruction Frame can be
omitted on all instructions except the first instruction after the
REPEAT is issued. REPEAT is most useful for memory
instructions (LD,ST,LDS,STS), but all instructions can be repeated,
except the REPEAT instruction itself.
The DATA_SIZE opcode field refers to the size of the repeat value. Only byte
size (up to 255 repeats) is supported. The instruction that is loaded directly after the
REPEAT instruction will be repeated RPT_0 times.
The instruction will be issued a total of RPT_0 + 1 times. An ongoing
repeat can only be aborted by sending a BREAK character.
REPEAT
Instruction Operation
The Figure above gives an example of repeat operation with a
ST instruction using pointer post increment operation. After the
REPEAT instruction is sent with RPT_0 =
n, the first ST instruction is issued
with SYNCH- and Instruction frame, while the next n
ST-instructions are executed by only sending in data bytes according to
the ST operand DATA_SIZE, and maintaining the
Acknowledge (ACK) handshake protocol.
If using indirect addressing instructions (LD/ST) it is recommended to
always use the pointer post increment option when combined with REPEAT
. Otherwise the same address will be accessed in all repeated access operations. For
direct addressing instructions (LDS/STS), the address must always be
transmitted as specified in the instruction protocol, before data can be received
(LDS) or sent (STS).