15.5.7 Physical memory access via CoreSight

Although CoreSight does not require it, most CoreSight implementations provide a direct way to access the bus or buses of the target system. They do this by providing a Memory Access Port (MEM-AP) which is accessed through the CoreSight DAP. There are several types of MEM-AP depending on the type of the system bus. The three main types are APB-AP, AHB-AP, and AXI-AP, which provide access to APB, AHB, and AXI bus types respectively. Each of these access ports implements the CoreSight MEM-AP interface.

The following figure shows a simple, but typical, arrangement of MEM-APs:

Figure 15-8 MEM-AP Access Ports
MEM-AP Access Ports


To allow direct memory access through one of the MEM-APs, a DTSL configuration can create device objects for the MEM-APs themselves. When the memory access methods are called on such devices, the memory access is directed straight onto the system bus, completely bypassing the core or cores.

Note:

The memory access is not processed by the core MMU (so there is no core MMU address translation), and bypasses any cache in the core, which might result in a different value being observed to that observed by the core.
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