Programmer’s Reference

4.1.3SDRAM accesses

The Integrator memory map provides a 256MB address space for SDRAM. When a smaller sized SDRAM DIMM is fitted, it is mapped repeatedly to fill the 256MB space. For example, a 64MB DIMM appears four times, as shown in Figure 4-2.

0x0FFFFFFF

64MB

Local SDRAM

 

(repeat image)

 

 

 

64MB

Local SDRAM

 

(repeat image)

 

 

 

64MB

Local SDRAM

(repeat image)

 

 

 

 

64MB

Local SDRAM

 

 

0x0003FFFF

 

 

256KB

SSRAM

Figure 4-2 SDRAM repeat mapping for a 64MB DIMM

Local SDRAM

The local processor can access the local SDRAM (that is, the SDRAM on the same core module) at 0x00000000 to 0x0FFFFFFF in the core module address space. However, the lowest 256KB (0x00000000 to 0x0003FFFF) is hidden by the SSRAM or boot ROM, depending upon whether the core module is attached to a motherboard and upon the state of the REMAP bit.

The SDRAM cannot be accessed within this address space, although it can be accessed at one of its repeat images or at its alias location. In the case of a 256MB DIMM which fills the local SDRAM space, the first 256KB can only be accessed at the alias location (see System bus accesses to SDRAM below).

4-4

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