Datasheet

264
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
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
21.10 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
0
1
2
3
4
5
EPEN=1
ALLOC=1
Free memory
0
1
2
4
5
EPEN=0
(ALLOC=1)
Free memory
0
1
2
4
5
Endpoints
activation
Endpoint Disable
Free its memory
(ALLOC=0)
Free memory
0
1
2
3 (bigger size)
5
Endpoint
Activatation
Lost memory
4
Conflict