Nexus 3 Read/Write Access To Memory-Mapped Resources - STMicroelectronics SPC572L series Reference Manual

RM0400
66.17

Nexus 3 Read/Write access to memory-mapped resources

The Read/Write access feature allows access to memory-mapped resources via the
JTAG/OnCE port. The Read/Write mechanism supports single as well as block reads and
writes to AHB resources.
The Nexus 3 module is capable of accessing resources on the system bus (AHB). Memory-
mapped registers and other non-cached memory can be accessed via the standard memory
map settings.
All accesses are setup and initiated by the Read/Write Access Control/Status Register
(RWCS), as well as the Read/Write Access Address (RWA) and Read/Write Access Data
Registers (RWD). Nexus 3 read/write accesses are run as privileged data non-cacheable
accesses by default, and drive the p_d_hprot[5:0] bus access attributes to 6'b000011
accordingly. The RWCS
modified when performing read or write accesses using the Nexus 3 Read/Write access
mechanism.
Using the Read/Write Access Registers (RWCS/RWA/RWD), memory mapped AHB
resources can be accessed through Nexus 3. The following subsections describe the steps
required to access memory-mapped resources.
Note: Read/Write Access can only access memory mapped resources when system reset is de-
asserted and clocks are running.
Misaligned accesses are NOT supported in the Nexus 3 module.
Uncorrectable ECC errors on Nexus 3 read access will result in the RWD register being
updated with the raw data received.
66.17.1 Single write access
1. Initialize the Read/Write Access Address Register (RWA) through the access method
outlined in
follows:
a)
2. Initialize the Read/Write Access Control/Status Register (RWCS) through the access
method outlined in
the bits as follows:
a)
b)
c)
d)
e)
f)
Note: Access Count (CNT) of 14'h0000 or 14'h0001 will perform a single access.
3. Initialize the Read/Write Access Data Register (RWD) through the access method
outlined in
follows:
a)
4. The Nexus block will then arbitrate for the AHB system bus and transfer the data value
from the data buffer RWD Register to the memory mapped address in the Read/Write
field is provided to allow a portion of these default values to be
ATTR
Section 66.5, Nexus 3 Register Access via
Write Address 32h'xxxxxxxx (write address)
→
Section 66.5, Nexus 3 Register Access via
Access Control (AC) →
Map Select (MAP)
→
Access Priority (PR)
→
Read/Write (RW) 1b'1 (write access)
→
Word Size (SZ) 3b'0xx (32-bit, 16-bit, 8-bit)
→
Access Count (CNT)
→
Section 66.5, Nexus 3 Register Access via
Write Data 32h'xxxxxxxx (write data)
→
DocID027809 Rev 4
1b'1 (to indicate start access)
3b'000 (primary memory map)
2b'11 (highest priority)
14h'0000 or 14h'0001(single access)
e200z215An3 Nexus 3 Module
JTAG/OnCE. Configure as
JTAG/OnCE. Configure
JTAG/OnCE. Configure as
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