AMBA Crossbar Switch (AXBS)
PXN20 Microcontroller Reference Manual, Rev. 1
16-8 Freescale Semiconductor
16.2.1.3 Master General Purpose Control Registers (XBAR_MGPCRn)
The Master General Purpose Control Register (XBAR_MGPCR) controls the arbitration policy during
undefined length burst accesses. The AULB (Arbitrate on Undefined Length Bursts) field determines
whether or not arbitration occurs for the slave port the master owns when the master is performing
undefined length burst accesses.
The MGPCR can only be accessed in supervisor mode with 32-bit access.
16.3 Functional Description
This section describes the functionality of the AXBS in more detail.
16.3.1 Overview
The main goal of the AXBS is to increase overall system performance by allowing multiple masters to
communicate concurrently with multiple slaves. To maximize data throughput, it is essential to keep
arbitration delays to a minimum.
This section examines data throughput from the point of view of masters and slaves, detailing when the
AXBS stalls masters, or inserts bubbles on the slave side.
Address AXBS_BASE + 0x0F00 (XBAR_MGPCR7) Access: Supervisor read/write
0123456789101112131415
R0000000000000000
W
Reset0000000000000000
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
R0000000000000
AULB
W
Reset0000000000000000
Figure 16-4. Master General-Purpose Control Registers (XBAR_MGPCRn)
Table 16-6. XBAR_MGPCRn Field Descriptions
Field Description
AULB Arbitration on Undefined Length Bursts. This field is used to select the arbitration policy during undefined length
bursts by this master.
This field is cleared by hardware reset.
000 No arbitration during undefined length bursts
001 Arbitration allowed on every beat of an undefined length burst
010 Arbitration allowed after four beats of an undefined length burst
011 Arbitration allowed after eight beats of an undefined length burst
100 Arbitration allowed after sixteen beats of an undefined length burst
101–111 Reserved
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