At present, decode2 does some formatting of the input data for the
multiply unit - truncation to 32 bits for 32-bit operations and then
sign or zero extension to 65 bits. This is going to prevent forwarding
of results within the execute pipeline in future, so we move the
formatting to the first cycle of the multiply pipeline.
It turns out that we have a wasted cycle at the front of the multiply
pipe, because decode2 has a register at its output and multiply has
a register at its input. For now we use this cycle to do the data
formatting.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This adds code to writeback to format data and test the result
against zero for the purpose of setting CR0. The data formatter
is able to shift and mask by bytes and do byte reversal and sign
extension. It can also put together bytes from two input
doublewords to support unaligned loads (including unaligned
byte-reversed loads).
The data formatter starts with an 8:1 multiplexer that is able
to direct any byte of the input to any byte of the output. This
lets us rotate the data and simultaneously byte-reverse it.
The rotated/reversed data goes to a register for the unaligned
cases that overlap two doublewords. Then there is per-byte logic
that does trimming, sign extension, and splicing together bytes
from a previous input doubleword (stored in data_latched) and the
current doubleword. Finally the 64-bit result is tested to set
CR0 if rc = 1.
This removes the RC logic from the execute2, multiply and divide
units, and the shift/mask/byte-reverse/sign-extend logic from
loadstore2.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Paul Mackerras
Anton Blanchard