1050
11054A–ATARM–27-Jul-11
SAM9X25
1050
11054A–ATARM–27-Jul-11
SAM9X25
45.5
Programming Interface
45.5.1
Initialization
45.5.1.1
Configuration
Initialization of the EMAC configuration (e.g., loop-back mode, frequency ratios) must be done
while the transmit and receive circuits are disabled. See the description of the network control
register and network configuration register earlier in this document.
To change loop-back mode, the following sequence of operations must
be followed:
1.
Write to network control register to disable transmit and receive circuits.
2.
Write to network control register to change loop-back mode.
3.
Write to network control register to re-enable transmit or receive circuits.
Note:
These writes to network control register cannot be combined in any way.
45.5.1.2
Receive Buffer List
Receive data is written to areas of data (i.e., buffers) in system memory. These buffers are listed
in another data structure that also resides in main memory. This data structure (receive buffer
queue) is a sequence of descriptor entries as defined in
“Receive Buffer Descriptor Entry” on
. It points to this data structure.
Figure 45-2.
Receive Buffer List
To create the list of buffers:
1.
Allocate a number (
n
) of buffers of 128 bytes in system memory.
2.
Allocate an area 2
n
words for the receive buffer descriptor entry in system memory and
create
n
entries in this list. Mark all entries in this list as owned by EMAC, i.e., bit 0 of
word 0 set to 0.
3.
If less than 1024 buffers are defined, the last descriptor must be marked with the wrap
bit (bit 1 in word 0 set to 1).
4.
Write address of receive buffer descriptor entry to EMAC register
receive_buffer
queue pointer.
5.
The receive circuits can then be enabled by writing to the address recognition registers
and then to the network control register.
Receive Buffer Queue Pointer
(MAC Register)
Receive Buffer 0
Receive Buffer 1
Receive Buffer N
Receive Buffer Descriptor List
(In memory)
(In memory)
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