Memory

This document describes the memory system of RTL87x2G and introduces how to use it. RTL87x2G memory consists of ROM, RAM, Flash, and eFuse, as shown in Memory Layout. This flexible memory configuration mechanism allows RTL87x2G to support a wide range of application programs.

Memory Layout
Memory Type	Region	Start Addr	End Addr	Size(bytes)
ROM		0x00000000	0x0007FFFF	512K
RAM	ITCM1	0x00100000	0x0012FFFF	192K
	DTCM0	0x00130000	0x0013FFFF	64K
	DTCM1	0x00140000	0x0014FFFF	64K
	Data SRAM	0x00200000	0x00203FFF	16K
	Buffer SRAM	0x00280000	0x0028BFFF	48K
Cache	I-Cache			32K
Cache	D-Cache			16K
Flash	SPI Flash	0x04000000	0x07FFFFFF	64M*
eFuse	eFuse			1K

Note

* means the maximum mapping space is 64 MB, but the actual size depends on the used Flash memory size.

ROM

The ROM code is located at [0x0, 0x7FFFF), with a total size of 512KB, in which Bootloader, Flash Driver, Power Manager, Bluetooth Controller, and other platform modules are built in. RTL87x2G ROM opens some modules such as Flash Driver for applications to use. RTL87x2G SDK contains the header files of these ROM modules, which enable users to access built-in ROM functions. This reduces the application code size and RAM size.

RAM

Memory Space Layout

RAM is divided into three blocks, namely TCM, Data RAM, and Buffer RAM. Namely TCM with an address space of 0x00100000 ~ 0x0012FFFF with a total size of 192KB, DTCM0 with an address space of 0x00130000 ~ 0x0013FFFF with a total size of 64KB, and DTCM1 with an address space of 0x00140000 ~ 0x0014FFFF with a total size of 64KB. The three space addresses are consecutive.

TCM: A specially designed type of memory that focuses on providing low latency, high bandwidth, and deterministic access characteristics, containing ITCM and DTCM:
- ITCM: A type of TCM specifically used for storing program instructions, allowing the CPU to quickly access and execute the code.
- DTCM: A type of TCM specifically designed for storing data, enhancing the access speed to this data.

The RAM Space of RTL87x2G is divided into 5 parts. Five parts of RAM space can be used to store data and execute code.

RAM Space
Region	Starting Address	Address Range	Total Size
ITCM1	0x00100000	0x00100000~0x0012FFFF	192KB
DTCM0	0x00130000	0x00130000~0x0013FFFF	64KB
DTCM1	0x00140000	0x00140000~0x0014FFFF	64KB
Data SRAM	0x00200000	0x00200000~0x00203FFF	16KB
Buffer SRAM	0x00280000	0x00280000~0x0028BFFF	48KB

The memory space layout will be different for TrustZone enable and TrustZone disable, as follows:

TrustZone Disable Memory Space Layout

../../../../_images/TrustZone_disable_RAM_layout.png — TrustZone disable RAM Layout

Note

When TrustZone is disabled, there is no distinction between secure and non-secure.

Each part has a fixed arrangement sequence and a specific purpose, as shown in TrustZone disable RAM Usage.

TrustZone disable RAM Usage
Memory Type	Memory Usage	Memory Variable
S ROM data	Store global variables and static variables in Secure ROM Code	No
Main Stack	Used in startup and interrupt service routines	No
Boot Patch RAM	Store Boot Patch global variables and static variables and code executed on RAM	No
System Patch RAM	Store System Patch global variables, static variables, and code executed on RAM	No
Stack Patch RAM	Store Stack Patch global variables, static variables, and code executed on RAM	No
NS ROM data	Store global variables and static variables in Non-Secure ROM Code	No
DTCM + ITCM Heap	For the dynamic application space of Non-Secure ROM code, System Patch code, Non-Secure Upperstack code, and APP code	Yes
APP RAM	Store global variables, static variables, and code executed on RAM in APP	Yes
Bluetooth Host RAM	Store global variables, static variables, and code executed on RAM in Bluetooth Host	Yes

TrustZone Enable Memory Space Layout

../../../../_images/TrustZone_enable_RAM_layout.png — TrustZone enable RAM Layout

TrustZone enable RAM Usage
Memory Type	Memory Usage	Memory Variable
S ROM data	Store global variables and static variables in Secure ROM Code	No
Secure Main Stack	The stack is used in secure startup and interrupt service routines	No
Boot Patch RAM	Store Boot Patch global variables and static variables and code executed on RAM	No
System Patch RAM	Store System Patch global variables and static variables and code executed on RAM	No
Stack Patch RAM	Store Stack Patch global variables and static variables and code executed on RAM	No
NS ROM data	Store global variables and static variables in Non-Secure ROM Code	No
NS Main Stack	The stack is used in non-secure startup and interrupt service routines	No
Secure Heap	For the dynamic application space of Secure ROM code and SecureAPP code	Yes
Secure APP RAM	Store Secure APP global variables and static variables and code executed on RAM	Yes
NS DTCM + ITCM Heap	For the dynamic application space of Non-Secure ROM code, System Patch code, Bluetooth Host code and APP code	Yes
NS APP RAM	Store global variables and static variables in NS APP and code executed on RAM	Yes
Bluetooth Host RAM	Store global variables and static variables in Bluetooth Hostand code executed on RAM	Yes

The Adjustable RAM space is uniformly modified through different macro definitions in mem_config.h. NS_RAM_UPPERSTACK_SIZE must be set accordingly according to the version of the BT Host image used. Different BT Host images occupy different sizes of DTCM. Please pay attention to the BT Host release document and its description. Adjust the size of NS_RAM_UPPERSTACK_SIZE according to application needs.

Adjustable RAM space
Memory Type	Macro
Upperstack RAM	NS_RAM_UPPERSTACK_SIZE
APP RAM	NS_RAM_APP_SIZE
DTCM + ITCM Heap	NS_RAM_APP_RESERVED_SIZE - NS_RAM_APP_SIZE - NS_RAM_UPPERSTACK_SIZE

APIs

By calling the API: os_mem_alloc, memory can be dynamically applied for from DTCM Heap or Buffer SRAM Heap. The type of application is specified by the parameter ram_type, which corresponds to RAM_TYPE_DATA_ON and RAM_TYPE_BUFFER_ON. The specific code is as follows:

typedef enum
{
    RAM_TYPE_DATA_ON,        //DTCM Heap
    RAM_TYPE_DATA_OFF = RAM_TYPE_DATA_ON,
    RAM_TYPE_BUFFER_ON,
    RAM_TYPE_BUFFER_OFF = RAM_TYPE_BUFFER_ON,
    RAM_TYPE_EXT_DATA_SRAM,  //Ext DATA SRAM heap
    RAM_TYPE_NUM
} RAM_TYPE;

/**
* @brief  Allocate memory dynamically from Data RAM Heap or Buffer RAM heap
* @param  ram_type: specify which heap to allocate memory from
* @param  size: memory size in bytes to be allocated
* @retval pointer to the allocated memory
*/
#define os_mem_alloc(ram_type, size)
        os_mem_alloc_intern(ram_type, size, __func__, __LINE__)

Other APIs for dynamically applying for memory are as follows: (For details, refer to os_mem.h)

Dynamic Memory Allocation APIs
API	Description
os_mem_zalloc	allocated memory will be initialized to 0
os_mem_aligned_alloc	allocated memory will be aligned to the specified alignment
os_mem_free	free a memory block that had been allocated
os_mem_aligned_free	free an aligned memory block that had been allocated
os_mem_peek	get the unused memory size of the specified RAM type

Memory Usage Calculation

According to the way the APP uses RAM, it is divided into static area and dynamic area.

Statistics of Static Zone Size on APP RAM

Find the app.map file generated by Build to find the first address allocated in APP RAM, the end address, and the used size. By searching the map of the loading area ER_IRAM_NS Map, it is possible to determine the static usage of APP RAM.

../../../../_images/ER_IRAM_NS_Map.png — ER_IRAM_NS Map

Statistics of Remaining Heap Size

The remaining heap size of the specified RAM type can be obtained through the os_mem_peek function.

Adjust the RAM Available to APP

To further increase the total size of RAM available for the app, you can use the following two methods:

Modify some of the stack settings in the Stack interface of the MP Tool Config Setting, such as the number of Bluetooth links, AE, and PSD functions.

../../../../_images/MPTool_Stack_Config_Setting.png — Stack interface in MP Tool Config Setting

Disable log: Modify the Log interface in the MP Tool Config Setting to change the log to ‘log disable’.

Cache

RTL87x2G supports 32KB I-Cache and 16KB D-Cache.

Cache default policy:

Flash is cacheable by default.
Data SRAM and buffer SRAM are non-cacheable by default.

Flash

Refer to Flash.

PSRAM

Refer to PSRAM.

eFuse

eFuse is a block of one-time programming memory that is used to store important and fixed information, such as UUID, security key, and other one-time programming configurations. A single bit of eFuse cannot be changed from 0 to 1, and there is no erase operation for eFuse, so be careful when updating eFuse. Realtek offers MPTool to update certain eFuse sections.