15.01.2013 Views

U. Glaeser

U. Glaeser

U. Glaeser

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Issue<br />

Dispatch<br />

FIGURE 6.4 The processor core providing shelving with dispatch-bound operand fetching and renaming.<br />

the concerned rename registers will be changed from the “allocated, not valid” or “allocated, valid” state<br />

to the “available” state and the corresponding mappings between architectural and rename registers will<br />

be deleted.<br />

The Process of Renaming, Assuming Dispatch-Bound Operand Fetching<br />

Assuming basically the same processor core as before, but using the dispatch-bound operand fetching, the<br />

rename process is carried out as follows (see Fig. 6.4).<br />

(i) During instruction issue, both the destination register (Rd) and the source registers (Rs1 and Rs2) are renamed in the same way as described for issue bound operand fetching. But now, beyond the<br />

operation code (OC) and the renamed destination register identifier (Rd′), the renamed source register<br />

identifiers ( Rs1′ and Rs2′ ) are written into the RS rather than the operand values (Op1, Op2, if available)<br />

as with issue bound operand fetching.<br />

(ii) During dispatching two tasks need to be performed: (a) the instruction held in the last entry of<br />

the RS needs to be checked to see whether it is executable. If so and if the EU is also free, this instruction<br />

needs to be forwarded for execution to the EU. (b) During forwarding of the instruction, its operands<br />

need to be fetched either from the RRF or from the ARF in the same way as described in connection<br />

with the issue-bound operation.<br />

(iii) When the EU finishes its operation, the generated result is used to update the RRF. Updating is<br />

performed by writing the result into the allocated rename register using the supplemented register<br />

identifier (Rd′) as an index into the RRF and setting the associated valid bit (V-bit).<br />

© 2002 by CRC Press LLC<br />

Decoded instructions<br />

OC Rd, Rs1, Rs2<br />

Mapping<br />

table<br />

Rd' Rs2'<br />

Rs1'<br />

Reservation<br />

station (RS)<br />

OC Rd Rs1' Rs2'<br />

Update RRF<br />

Rename register<br />

file (RRF)<br />

Result, Rd'<br />

Rs1', Rs2'<br />

OC, Rd'<br />

V<br />

EU<br />

Checking for availability<br />

of (Rs1'), (Rs2')<br />

Op1<br />

Op2<br />

Architectural register<br />

file (ARF)<br />

Bypassing

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!