PXN20RM Datasheet, PDF (803/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Media Local Bus (MLB)
27.4.5 Channel Arbiter
The MLB Device includes a DMA Controller with a Host Bus that can access system memory. The
channel arbiter logic of the MLB Device, arbitrates requests between the different logical channel requests.
Some of the functions of the channel arbiter include:
• determining priorities of channel requests
• granting high priority requests based on round-robin arbitration of current high priority requests
• granting low priority requests based on round-robin arbitration of current low priority requests, and
• routing data and control information between channels and the Host Bus.
27.4.5.1 Round Robin Arbitration
The MLB channel arbiter uses round-robin arbitration to determine which logical channel is granted
access to the Host Bus. An example of the round-robin arbitration method is provided in Figure 27-18.
Round-Robin Arbitration: 4 Channel Example
g0 r0 r1 r2 r3
gn - Channel n grant
rn - Channel n request
g3 r0
g0 ^{r1 r2 r3}
Grant 0
(g0)
g0 r1
g3 r0 r1 r2 r3
Grant 3
(g3)
g3 r0 r1
g1 r2 r3
Grant 1
(g1)
g1 r0 r1 r2 r3
g2 r3
Grant 2
(g2)
g2 ^{r0 r1 r3}
g1 r2
g2 r0 r1 r2 r3
Figure 27-18. Round-Robin Arbitration Example
Freescale Semiconductor
PXN20 Microcontroller Reference Manual, Rev. 1
27-31