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Zynq-7000 AP SoC Technical Reference Manual www.xilinx.com 734
UG585 (v1.11) September 27, 2016
Chapter 29
On-Chip Memory (OCM)
29.1 Introduction
The on-chip memory (OCM) module contains 256 KB of RAM and 128 KB of ROM (BootROM). It
supports two 64-bit AXI slave interface ports, one dedicated for CPU/ACP access via the APU snoop
control unit (SCU), and the other shared by all other bus masters within the processing system (PS)
and programmable logic (PL). The BootROM memory is used exclusively by the boot process and is
not visible to the user.
OCM supports high AXI read and write throughput for RAM access by implementing the RAM as a
double-wide memory (128 bits). To take advantage of the high RAM access throughput, the user
application must use even AXI burst sizes and 128-bit aligned addresses.
The TrustZone feature is supported at 4-KB memory granularity. The entire 256 KB of RAM can be
divided into sixty four 4-KB blocks, and assigned security attributes independently. See Programming
ARM TrustZone Architecture on the Xilinx Zynq-7000 All Programmable SoC (UG1019).
As shown in Figure 29-1, there are 10 AXI channels associated with the OCM, five for the CPU/ACP
(SCU) port and five for the other PS/PL masters (OCM switch port). Arbitration between the read and
write channels of the SCU and OCM switch ports is performed within the OCM module. Parity
generation and checking is performed on RAM accesses only. Other main interfaces are an interrupt
signal (IRQ ID #35) as well as a register access APB port.