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The SELECT register selects the DP address bank, and also provides the address for other components in the system, which is used by the APB Master interface on the DP to drive the APB address line.
The address on the address line driven by SELECT register is set at the start of the transfer, and does not change until the next transfer. DPIDR1.ASIZE indicates the width, in bits, of the APB master interface address bus. It is defined by the configuration parameter APB_ADDR_WIDTH. The DP can only issue word-aligned addresses, so paddr[1:0] are always zero. Bits [3:2] come from APACC, and higher order bits come from the SELECT register. The size of the address in SELECT is defined in DPIDR1.ASIZE. Unimplemented address bits are WI.
The SELECT register characteristics are:
The following figure shows the bit assignments.
The following table shows the bit assignments.
Table 9-14 SELECT register bit assignments
Address Output bits [31:4]. Selects a four-word bank of system locations to access. Address bits [3:2] are provided with APACC transactions.
Debug Port Address bank select.