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Page 24
KM416RD8AC(D)/KM418RD8AC(D)
Direct RDRAM
Rev. 1.01 Oct. 1999
Interleaved Write - Example
Figure 20 shows an example of an interleaved write transac-
tion. Transactions similar to the one presented in Figure 16
are directed to non-adjacent banks of a single RDRAM. This
allows a new transaction to be issued once every t
RR
interval
rather than once every t
RC
interval (four times more often).
The DQ data pin efficiency is 100% with this sequence.
With two dualocts of data written per transaction, the COL,
DQA, and DQB pins are fully utilized. Banks are precharged
using the WRA autoprecharge option rather than the PRER
command in an ROWR packet on the ROW pins.
In this example, the first transaction is directed to device Da
and bank Ba. The next three transactions are directed to the
same device Da, but need to use different, non-adjacent
banks Bb, Bc, Bd so there is no bank conflict. The fifth
transaction could be redirected back to bank Ba without
interference, since the first transaction would have
completed by then (t
RC
has elapsed). Each transaction may
use any value of row address (Ra, Rb, ..) and column address
(Ca1, Ca2, Cb1, Cb2, ...).
Interleaved Read - Example
Figure 21 shows an example of interleaved read transac-
tions. Transactions similar to the one presented in Figure 15
are directed to non-adjacent banks of a single RDRAM. The
address sequence is identical to the one used in the previous
write example. The DQ data pins efficiency is also 100%.
The only difference with the write example (aside from the
use of the RD command rather than the WR command) is
the use of the PREX command in a COLX packet to
precharge the banks rather than the RDA command. This is
done because the PREX is available for a readtransaction but
is not available for a masked write transaction.
Interleaved RRWW - Example
Figure 22 shows a steady-state sequence of 2-dualoct
RD/RD/WR/WR.. transactions directed to non-adjacent
banks of a single RDRAM. This is similar to the interleaved
write and read examples in Figure 20 and Figure 21 except
that bubble cycles need to be inserted by the controller at
read/write boundaries. The DQ data pin efficiency for the
example in Figure 22 is 32/42 or 76%. If there were more
RDRAMs on the Channel, the DQ pin efficiency would
approach 32/34 or 94% for the two-dualoct RRWW
sequence (this case is not shown).
In Figure 22, the first bubble type t
CBUB1
is inserted by the
controller between a RD and WR command on the COL
pins. This bubble accounts for the round-trip propagation
delay that is seen by read data, and is explained in detail in
Figure 4. This bubble appears on the DQA and DQB pins as
t
DBUB1
between a write data dualoct D and read data dualoct
Q. This bubble also appears on the ROW pins as t
RBUB1
.
Figure 20: Interleaved Write Transaction with Two Dualoct Data Length
CTM/CFM
DQA8..0
DQB8..0
COL4
..COL0
ROW2
..ROW0
T
0
T
4
T
8
T
12
T
1
T
5
T
9
T
13
T
2
T
6
T
10
T
14
T
3
T
7
T
11
T
15
T
16
T
20
T
24
T
28
T
17
T
21
T
25
T
29
T
18
T
22
T
26
T
30
T
19
T
23
T
27
T
31
T
32
T
36
T
40
T
44
T
33
T
37
T
41
T
45
T
34
T
38
T
42
T
46
T
35
T
39
T
43
T
47
ACT a0
MSK (b2)
WRA c2
MSK (b1)
WR c1
WR b1
MSK (a1)
WRA b2
MSK (a2)
D (b2)
D (b1)
ACT b0
ACT c0
ACT d0
ACT e0
D (a2)
D (a1)
WR d1
MSK (c1)
D(c1)
ACT f0
WR d2
MSK (c2)
WR e1
MSK (d1)
D (c2)
D (d1)
WR e2
MSK (d2)
D (z2)
D (z1)
D (x2)
D (y1)
D (y2)
MSK (z2)
t
CWD
WRA a2
MSK (z1)
WR a1
WR z1
MSK (y1)
WRA z2
MSK (y2)
Q (d1)
t
RCD
t
RC
Transaction e can use the
same bank as transaction a
t
RR
f3 = {Da,Ba+2}
Transaction f: WR
f0 = {Da,Ba+2,Rf}
f1 = {Da,Ba+2,Cf1}
f2= {Da,Ba+2,Cf2}
e3 = {Da,Ba}
Transaction e: WR
e0 = {Da,Ba,Re}
e1 = {Da,Ba,Ce1}
e2= {Da,Ba,Ce2}
d3 = {Da,Ba+6}
Transaction d: WR
d0 = {Da,Ba+6,Rd}
d1 = {Da,Ba+6,Cd1}
d2= {Da,Ba+6,Cd2}
c3 = {Da,Ba+4}
Transaction c: WR
c0 = {Da,Ba+4,Rc}
c1 = {Da,Ba+4,Cc1}
c2= {Da,Ba+4,Cc2}
b3 = {Da,Ba+2}
Transaction b: WR
b0 = {Da,Ba+2,Rb}
b1 = {Da,Ba+2,Cb1}
b2= {Da,Ba+2,Cb2}
a3 = {Da,Ba}
Transaction a: WR
a0 = {Da,Ba,Ra}
a1 = {Da,Ba,Ca1}
a2= {Da,Ba,Ca2}
z3 = {Da,Ba+6}
Transaction z: WR
z0 = {Da,Ba+6,Rz}
z1 = {Da,Ba+6,Cz1}
z2= {Da,Ba+6,Cz2}
y3 = {Da,Ba+4}
Transaction y: WR
y0 = {Da,Ba+4,Ry}
y1 = {Da,Ba+4,Cy1}
y2= {Da,Ba+4,Cy2}