OBI Memory Controller (hsid_x_obi_mem)

This module performs memory read requests through the OBI bus, starting from an initial address and continuing for a specified number of reads.

At the RTL level, access to the OBI interface is implemented using a structure derived directly from the X-HEEP project, similar to the Register Interface described in the module hsid_x_registers. The structure is defined in the package hsid_x_obi_inf_pkg.sv, located in the directory hw/src/hsid_pkg/rtl.

Memory read requests are issued according to the OBI protocol. A read request for a 32-bit word is initiated by asserting the signals req = 1, we = 0, and be = 0xF, and by placing the desired address on addr. Once the request is accepted, the memory address is incremented by 4, and the process is repeated until the required number of requests has been issued. For each accepted request, the module waits to receive a response from the bus.
The figure below shows an example of four consecutive memory reads.

The control of these read operations is implemented through a simple FSM, shown in the figure below. In the HOXM_INIT state, read requests are prepared using the initial address provided by the initial_addr signal. The module then transitions to the HOXM_READING state, during which consecutive read requests are issued until the final valid memory response is received.