ATmega16U4 datasheet(262/408 Pages) ATMEL

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262

7766D–AVR–01/09

ATmega16U4/ATmega32U4

The following figure illustrates the allocation and reorganization of the USB memory in a typical

example:

Table 21-1.

Allocation and reorganization USB memory flow

• First, Endpoint 0 to Endpoint 5 are configured, in the growing order. The memory of each is

reserved in the DPRAM.

• Then, the Endpoint 3 is disabled (EPEN=0), but its memory reservation is internally kept by

the controller.

• Its ALLOC bit is cleared: the Endpoint 4 “slides” down, but the Endpoint 5 does not “slide”.

• Finally, if the firmware chooses to reconfigure the Endpoint 3, with a bigger size. The

controller reserved the memory after the Endpoint 2 memory and automatically “slide” the

Endpoint 4. The Endpoint 5 does not move and a memory conflict appear, in that both

Endpoint 4 and 5 use a common area. The data of those endpoints are potentially lost.

Note that:

• the data of Endpoint 0 are never lost whatever the activation or deactivation of the higher

Endpoint. Its data is lost if it is deactivated.

• Deactivate and reactivate the same Endpoint with the same parameters does not lead to a

“slide” of the higher endpoints. For those endpoints, the data are preserved.

• CFGOK is set by hardware even in the case where there is a “conflict” in the memory

allocation.

21.8

PAD suspend

The next figures illustrates the pad behaviour:

• In the “idle” mode, the pad is put in low power consumption mode.

• In the “active” mode, the pad is working.

Free memory

EPEN=1

ALLOC=1

Free memory

EPEN=0

(ALLOC=1)

Free memory

Endpoints

activation

Endpoint Disable

Free its memory

(ALLOC=0)

Free memory

3 (bigger size)

Endpoint

Activatation

Lost memory

Conflict

ATmega16U4 Datasheet(PDF) 262 Page - ATMEL Corporation

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