
TM1100 Preliminary Data Book
Philips Semiconductors
19-6
PRELIMINARY INFORMATION
File: arb.fm5, modified 7/23/99
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 rarely many devices issue re-
quests at exactly the same time (but 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} equa-
tions 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.
19.5.2
Analysis of Bandwidth
In the following, ceil(x) means the least integral value
greater than or equal to x.
Minimum allocated bandwidth, Bx for a device x, by the
arbiter 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 TM1100, S is equal to 64 (bytes).
Ex is the ratio of requests available for a device x accord-
ing to the arbiter settings.
It means the device x will get 1 / Ex out of the total re-
quests. Ex is derived from the arbiter settings as follows:
Where
D
DVDD
ceil
21101
++++
1
----------------------------------------
D
6
×
1
+
=
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
21101
++++
2
----------------------------------------
E
6
×
=
E
AI
21101
++++
1
----------------------------------------
E
6
×
=
E
AO
21101
++++
1
----------------------------------------
E
6
×
=
E
DVDD
21101
++++
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
×
=