| 摘要 |
An address generator for generating addresses for target locations in a circular buffer of length L, the buffer having an upper boundary and a lower boundary, the lower boundary being at an address which is a multiple of an integer power of two, and the address of a target location being offset by M locations from a current buffer location at address A, where M is no longer than L. The apparatus comprises a set of three registers, an adder for generating an absolute address, an adder/subtractor for generating a wrapped address which maps the absolute address into the buffer address space when the absolute address is outside that space, and certain control logic for selecting as the target address either the absolute address or the wrapped address. The contents of the three registers represent, respectively, the length of the buffer, the current address designated by the pointer, and the offset from the current buffer address to the target location in the buffer. The adder generates the absolute address by adding the current address of the pointer to the offset. The adder/subtractor generates the wrapped address by either adding to the absolute address or subtracting from the absolute address the length of the buffer, depending on the direction of the offset. Logic operating on the carry bits from the adder and from the adder/substractor detects the generation of an absolute address outside the boundaries of the buffer and provides as the target address the wrapped address instead of the absolute address.
|
