Digi NS9750 User Manual
Page 284
S y s t e m b u s a r b i t e r
2 6 0
N S 9 7 5 0 H a r d w a r e R e f e r e n c e
The available bandwidth per master is calculated using this formula:
Bandwidth per master:
= [(100MHz/2) / (16 clock cycles per access x 6 masters)] x 32 bytes
= 16.667 Mbytes/master
If the LCD is configured for two arbiter channel slots, then, there are 33.334 Mbytes
available, which is greater than the 25 Mbytes required. Each of the other masters
have 16.667 Mbytes available, which is more than enough to meet their
requirements.
Note:
When assigning two arbiter channel slots to a master, the slot assignments
should be spaced equally.
The AHB arbiter will be programmed as follows:
BRC0[31:24]
= 8’b1_0_00_0000
channel enabled, 100%, ARM926EJ-S
BRC0[23:16]
= 8’b1_0_00_0001
channel enabled, 100%, Ethernet Rx
BRC0[15:8]
= 8’b1_0_00_0000
channel enabled, 100%, ARM926EJ-S
BRC0[7:0]
= 8’b1_0_00_0010
channel enabled, 100%, Ethernet Tx
BRC1[31:24]
= 8’b1_0_00_0000
channel enabled, 100%, ARM926EJ-S
BRC1[23:16]
= 8’b1_0_00_0110
channel enabled, 100%, LCD first slot
BRC1[15:8]
= 8’b1_0_00_0000
channel enabled, 100%, ARM926EJ-S
BRC1[7:0]
= 8’b1_0_00_0100
channel enabled, 100%, PCI
BRC2[31:24]
= 8’b1_0_00_0000
channel enabled, 100%, ARM926EJ-S
BRC2[23:16]
= 8’b1_0_00_0101
channel enabled, 100%, BBus
BRC2[15:8]
= 8’b1_0_00_0000
channel enabled, 100%, ARM926EJ-S
BRC2[7:0]
= 8’b1_0_00_0110
channel enabled, 100%, LCD second slot
BRC3[31:24]
= 8’b0_0_00_0000
channel disabled
BRC3[23:16]
= 8’b0_0_00_0000
channel disabled
BRC3[15:8]
= 8’b0_0_00_0000
channel disabled
BRC[7:0]
= 8’b0_0_00_0000
channel disabled
Note that the BBus requires 4 Mbytes but has been allocated 16.667 Mbytes. The BBus
bandwidth can be reduced using the bandwidth reduction field (in the BRC registers).
To reduce the available bandwidth by 25% to 4.167 Mbytes, for example, the 2-bit
field can be set to
2’b11
. This restricts the BBus master when the system is fully
loaded. The new configuration for BBus is:
BRC2[23:16]
= 8’b1_0_11_0101
channel enabled, 25%, BBus