
TM1300 Data Book
Philips Semiconductors
20-6
PRODUCT SPECIFICATION
Where
As an example, if CPUweight is 3, L2weight is 2, VOweight
is 3 and L3weight is 7, then
D2 is ceil[(3 + 2) / 2] = 3,
DVO is ceil[(3 + 7) / 3] * 3 +1 = 13.
If CPU/SDRAM ratio is 5/4 (for example memory fre-
quency is 80 MHz and CPU frequency is 100 MHz), re-
fresh interval Kd is 1220 cycles, and Rx is 2, then the
maximum latency for VO is:
LVO,sc = 13 * 20 + 10 + ceil[13 * 20 / 1220] * 19 +
ceil(16 * 2 / (5 / 4)] = 315 SDRAM cycles
LVO = LVO,sc * 12.5 = 3937.5 ns
Note: Average latency is normally much lower than worst
case latency because on rare occasions many units will
issue requests at exactly the same time (this is assumed
when evaluating the maximum latency).
Note: All real-time units have a special exception notifi-
cation flag that is raised if an overflow or underflow oc-
curs while operating.
Note: To compute the latency Lx when a unit is not en-
abled, its weight has to be set to ‘0’ in the D{2,3,4,5,6}
equations and in D{AI,AO,VLD} for AI, AO or VLD.
These equations are not accurate for all the weights, but
give an upper bound of the worst case (which is usually
too pessimistic).
A much more accurate number could be found by simu-
lating the arbiter, e.g. if the settings are: CPUweight=1,
L2weight=2, VOweight=1 and L3weight=1, then
DVO = ceil[(1 + 1) / 1] * ceil[(1 + 2) / 2]
giving 4 requests. But actually the worst case grant re-
quests order is: CPU, L3, VO - resulting in 3 requests
only.
20.5.2
Bandwidth Analysis
In the following, ceil(x) means the least integral value
greater than or equal to x.
Minimum allocated bandwidth, Bx for a unit x, by the ar-
biter is defined as follows:
Bx = (Mcycles - Kk) * S / [T * Ex + (16 * Rx / C)]
Where:
Mcycles is the total amount of SDRAM cycles available in
a period P in which the bandwidth is computed. For ex-
ample, if the period is 1 second and SDRAM runs at 80
MHz then Mcycles is 80,000,000.
Kk is the amount of SDRAM cycles used by the refresh
during the same period P.
If P is in seconds it could be expressed as:
Kk = ceil(4096 * P / .064) * K
For example, if P is 1 second then Kk is
ceil(4096 * 1 / .064) * 19 = 1216000 SDRAM cycles.
S is the size of the transaction on the bus.
For TM1300, S is equal to 64 (bytes).
Ex is the ratio of requests available for a unit x according
to the arbiter settings.
It means the unit x will get 1 / Ex out of the total requests.
Ex is derived from the arbiter settings as follows:
Where:
D
2
ceil
CPU
weight
L2
weight
+
L2
weight
-------------------------------------------------------
=
D
3
ceil
VO
weight
L3
weight
+
L3
weight
--------------------------------------------------
D
2
×
=
D
4
ceil
ICP
weight
L4
weight
+
L4
weight
----------------------------------------------------
D
3
×
=
D
5
ceil
VI
weight
L5
weight
+
L5
weight
------------------------------------------------
D
4
×
=
D
6
ceil
PCI
weight
L6
weight
+
L6
weight
----------------------------------------------------
D
5
×
=
E
CPU
weight
L2
weight
+
CPU
weight
-------------------------------------------------------
=
E
VO
weight
L3
weight
+
VO
weight
---------------------------------------------------
E
2
×
=
E
ICP
weight
L4
weight
+
ICP
weight
----------------------------------------------------
E
3
×
=
E
VI
weight
L5
weight
+
VI
weight
------------------------------------------------
E
4
×
=
E
PCI
weight
L6
weight
+
PCI
weight
----------------------------------------------------
E
5
×
=
E
VLD
211011
+++++
2
-------------------------------------------------
E
6
×
=
E
AI
211011
+++++
1
-------------------------------------------------
E
6
×
=
E
AO
211011
+++++
1
-------------------------------------------------
E
6
×
=
E
DVDD
211011
+++++
1
-------------------------------------------------
E
6
×
=
E
SPDO
211011
+++++
1
-------------------------------------------------
E
6
×
=
E
2
CPU
weight
L2
weight
+
L2
weight
-------------------------------------------------------
=
E
3
VO
weight
L3
weight
+
L3
weight
--------------------------------------------------
E
2
×
=
E
4
ICP
weight
L4
weight
+
L4
weight
----------------------------------------------------
E
3
×
=