
EM358x
Rev. 0.4
17
2.2.1.5
Simulated EEPROM
Ember software reserves 8 kB of the main flash block as a simulated EEPROM storage area for stack and
customer tokens. The simulated EEPROM storage area implements a wear-leveling algorithm to extend the
number of simulated EEPROM write cycles beyond the physical limit of 20,000 write cycles for which each flash
cell is qualified.
2.2.2
RAM
2.2.2.1
RAM Overview
The EM358x has either 32 or 64 kB of static RAM on-chip. The start of RAM is mapped to address 0x20000000.
Although the ARM
®
Cortex
TM
-M3 allows bit band accesses to this address region, the standard MPU configuration
does not permit use of the bit-band feature.
The RAM is physically connected to the AHB System bus and is therefore accessible to both the ARM
®
Cortex
TM
-
M3 microprocessor and the debugger. The RAM can be accessed for both instruction and data fetches as bytes,
half words, or words. The standard MPU configuration does not permit execution from the RAM, but for special
purposes the MPU may be disabled. To the bus, the RAM appears as 32-bit wide memory and in most situations
has zero wait state read or write access. In the higher CPU clock mode the RAM requires one wait state. This is
handled by hardware transparent to the user application with no configuration required.
2.2.2.2
Direct Memory Access (DMA) to RAM
Several of the peripherals are equipped with DMA controllers allowing them to transfer data into and out of RAM
autonomously. This applies to the radio (802.15.4-2003 MAC), general purpose ADC, USB device controller and
the two serial controllers. In the case of the serial controllers, the DMA is full duplex so that a read and a write to
RAM may be requested at the same time. Thus there are six DMA channels in total. See Chapter 8, Section 8.7
and Chapter 11, Section 11.1.4 for a description of how to configure the serial controllers and ADC for DMA
operation. The DMA channels do not use AHB system bus bandwidth as they access the RAM directly.
The EM358x integrates a DMA arbiter that ensures fair access to the microprocessor as well as the peripherals
through a fixed priority scheme appropriate to the memory bandwidth requirements of each master. The priority
scheme is as follows, with the top peripheral being the highest priority:
1.
USB Device Controller (where applicable)
2.
General Purpose ADC
3.
Serial Controller 2 Receive
4.
Serial Controller 2 Transmit
5.
MAC
6.
Serial Controller 1 Receive
7.
Serial Controller 1 Transmit
2.2.2.3
RAM Memory Protection
The EM358x integrates a memory protection mechanism through the ARM
®
Cortex
TM
-M3 Memory Protection Unit
(MPU) described in the Memory Protection Unit section. The MPU may be used to protect any area of memory.
MPU configuration is normally handled by Ember software.
2.2.3
Registers
Appendix A, Register Address Table provides a short description of all application-accessible registers within the
EM358. Complete descriptions are provided at the end of each applicable peripheral’s description. The registers
are mapped to the system address space starting at address 0x40000000. These registers allow for the control
and configuration of the various peripherals and modules. The CPU only performs word-aligned accesses on the
system bus. The CPU performs a word aligned read-modify-write for all byte, half-word, and unaligned writes and
a word-aligned read for all reads. Silicon Labs recommends accessing all peripheral registers using word-aligned
addressing.
As with the RAM, the peripheral registers fall within an address range that allows for bit-band access by the ARM
®
Cortex
TM
-M3, but the standard MPU configuration does not allow access to this alias address range.
Содержание EMBER EM358 series
Страница 2: ...EM358x 2 Rev 0 4 ...
Страница 7: ...EM358x Rev 0 4 7 ...