34.3.3.7 REPEAT - Set Instruction Repeat Counter

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.

The figure above gives an example of repeat operation with an 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).