the sid::bus interface

Reading

        status read (host_int_4 addr, little_int_1& data);

        status read (host_int_4 addr, little_int_2& data);

        status read (host_int_4 addr, little_int_4& data);

        status read (host_int_4 addr, little_int_8& data);

        status read (host_int_4 addr, big_int_1& data);

        status read (host_int_4 addr, big_int_2& data);

        status read (host_int_4 addr, big_int_4& data);

        status read (host_int_4 addr, big_int_8& data);      
      

To read from a bus, the bus master calls the overloaded function read with an address to read from, and a reference to a data word. Addresses are conventionally interpreted as byte addresses. If the read is successful, the data word will contain the word read; otherwise it will be unchanged.

Writing

        status write (host_int_4 addr, little_int_1 data);

        status write (host_int_4 addr, little_int_2 data);

        status write (host_int_4 addr, little_int_4 data);

        status write (host_int_4 addr, little_int_8 data);

        status write (host_int_4 addr, big_int_1 data);

        status write (host_int_4 addr, big_int_2 data);

        status write (host_int_4 addr, big_int_4 data);

        status write (host_int_4 addr, big_int_8 data);      
      

To write to a bus, the bus master calls the overloaded function write with an address to write to, and a data word. Addresses are conventionally interpreted as byte addresses. The result of a write indicates whether the write was considered, by the bus slave, to be successful. Note however that the slave is not in any way required to reflect the contents of a successful write in terms of any future reads from the same address.

Status codes

All bus transactions are initiated by a bus master, and respond with a status code object. Such an object has the following fields:

The sid::bus::status class has simple zero-, one- and two-argument constructors, indicating general zero-latency success, success status alone (with zero latency) or status and latency of the bus transaction. For example, one can return from a bus transaction with any of the following statements:

      return status ();           // status = ok, latency = 0

      return status (unmapped);   // status = unmapped, latency = 0

      return status (ok, 5);      // status = ok, latency = 5