6.1.4.5 Unimplemented Address Space

The AHB bus matrix performs address decoding based on the memory map defined in Figure 6-12 and Figure 6-13, to decide which slave, if any, is being addressed. Any access to memory space outside of these regions is considered unimplemented from the AHB bus matrix point of view. This access results in the assertion of a SW_ERRORSTATUS register bit of the MSS_EXTERNAL_SR control register, as well as the assertion of HRESP by the AHB bus matrix to the master. If any master attempts a write access to unimplemented address space, the AHB bus matrix completes the handshake to the master with an HRESP error indication. No write occurs to any slave.

If any master attempts a read access from unimplemented address space, the AHB bus matrix completes the handshake to the master with an HRESP error indication. Undefined data is returned. There may be further memory areas that are unimplemented, within individual slave memory regions. Depending on the slave, accesses may be aliased within these areas or not. Firmware must not perform writes to these locations because the aliasing may cause a write to another location within the slave. Data read from these intra-slave unimplemented regions may be undefined.