Altera DDR SDRAM High-Performance Controllers and ALTMEMPHY IP - Manual (Page 131)

Chapter 8: Timing Diagrams 8–3
DDR and DDR2 High-Performance Controllers II
June 2011 Altera Corporation External Memory Interface Handbook Volume 3
Section I. DDR and DDR2 SDRAM Controllers with ALTMEMPHY IP User Guide
1. The user logic requests the first read by asserting the local_read_req signal, and
the size and address for this read. In this example, the request is a burst of length
of 2 to the local address 0×000000. This local address is mapped to the following
memory address in half-rate mode:
mem_row_address = 0×000000
mem_col_address = 0×0000
mem_bank_address = 0×00
2. The user logic initiates a second read to a different memory column within the
same row. The request for the second write is a burst length of 2. In this example,
the user logic continues to accept commands until the command queue is full.
When the command queue is full, the controller deasserts the local_ready signal.
The starting local address 0x000002 is mapped to the following memory address in
half-rate mode:
mem_row_address = 0×0000
mem_col_address = 0×0002<<2 = 0×0008
mem_bank_address = 0×00
3. The controller issues the first read memory command and address signals to the
ALTMEMPHY megafunction for it to send to the memory device.
4. The controller asserts the afi_doing_rd signal to indicate to the ALTMEMPHY
megafunction the number of clock cycles of read data it must expect for the first
read. The ALTMEMPHY megafunction uses the afi_doing_rd signal to enable its
capture registers for the expected duration of memory burst.
5. The ALTMEMPHY megafunction issues the first read command to the memory
and captures the read data from the memory.
6. The ALTMEMPHY megafunction returns the first data read to the controller after
resynchronizing the data to the phy_clk domain, by asserting the
afi_rdata_valid
signal when there is valid read data on the afi_rdata bus.
7. The controller returns the first read data to the user by asserting the
local_rdata_valid signal when there is valid read data on the local_rdata bus. If
the ECC logic is disabled, there is no delay between the afi_rdata and the
local_rdata
buses. If there is ECC logic in the controller, there is one or three clock
cycles of delay between the afi_rdata and local_rdata buses.