Visible to Intel only — GUID: jka1458773541010
Ixiasoft
Visible to Intel only — GUID: jka1458773541010
Ixiasoft
6.1.8.4. Using the Address Span Extender
This example shows when and how to use address span extender component in your Platform Designer design.
In the above design, a 32-bit host shares 4 GB SDRAM with an external streaming interface. The host has the path to access streaming data from the SDRAM DDR memory. However, if you connect the whole 32-bit address bus of the host to the SDRAM DDR memory, you cannot connect the host to peripherals such as LED or UART. To avoid this situation, you can implement the address span extender between the host and DDR memory. The address span extender allows the host to access the SDRAM DDR memory and the peripherals at the same time.
To implement address span extender for the above example, you can divide the address window of the address span extender into two sub-windows of 512 MB each. The sub-window 0 is for the host program area. You can dynamically map the sub-window 1 to any area other than the program area.
You can change the offset of the address window by setting the base address of sub-window 1 to the control register of the address span extender. However, you must make sure that the sub-window address span masks the base address. You can choose any arbitrary base address. If you set the value 0xa000_0000 to the control register, Platform Designer maps the sub-window 1 to 0xa000_0000.
Address | Data |
---|---|
0x8000_0000 |
0x0000_0000 |
0x8000_0008 |
0xa000_0000 |
The table below indicates the Platform Designer parameter settings for this address span extender example.
Parameter | Value | Description |
---|---|---|
Datapath Width |
32 bits |
The CPU has 32-bits data width and the SDRAM DDR memory has 512-bits data width. Since the transaction between the host and SDRAM DDR memory is minimal, set the datapath width to align with the upstream host. |
Expanded Master Byte Address |
32 bits |
The address span extender has a 4 GB address span. |
Slave Word Address Width |
18 bits |
There are two 512 MB sub-windows in reserve for the host. The number of bytes over the data word width in the Datapath Properties (4 bytes for this example) accounts for the slave address. |
Burstcount Width |
4 bits |
The address span extender must handle up to 8 words burst in this example. |
Number of sub-windows |
2 |
Address window of the address span extender has two sub-windows of 512 MB each. |
Enable Slave Control Port |
true |
The address span extender component must have control to change the base address of the sub-window. |
Maximum Pending Reads |
4 |
This number is the same as SDRAM DDR memory burst count. |