Introduction

This chapter introduces the default memory layout of RTL8721Dx and how to modify the memory layout if needed.

RAM Layout

In total, there are 512KB SRAM on chip, and the size of PSRAM can be 0MB/4MB/8MB/16MB…, which is decided by users. The RAM layout is illustrated below.

RAM layout

SRAM0 (First 40KB) Layout

The first 40KB SRAM0 layout is illustrated in the following figure and table. It is the same for all situations.

SRAM0 (first 40KB) layout

SRAM0 (first 40KB) layout

Items	Start address	Size	Description	Mandatory
KM0_ROM_BSS_RAM	0x2000_0000	4KB	KM0 ROM BSS	√
KM0_MSP_RAM	0x2000_1000	4KB	KM0 Main Stack Pointer	√
KM0_STDLIB_HEAP_NS	0x2000_2000	4KB	KM0 ROM STDLIB heap	√
KM4_MSP_NS	0x2000_3000	4KB	KM4 non-secure Main Stack Pointer	√
KM4_ROM_BSS_COMMON	0x2000_4000	3.25KB	KM4 ROM secure and non-secure common BSS	√
KM0_BOOT_RAM	0x2000_4D00	64B	KM0 IMG2 entry	√
KM0_IPC_RAM	0x2000_4E00	512B	Exchange messages between cores	√
KM4_ROM_BSS_NS	0x2000_5000	4KB	KM4 ROM non-secure common BSS	√
KM4_STDLIB_HEAP_NS	0x2000_6000	4KB	KM4 ROM non-secure STDLIB heap	√
KM4_ROM_BSS_S	0x3000_7000	4KB	KM4 ROM secure-only BSS	√
KM0_RTOS_STATIC_0_NS	0x2000_8000	4KB	KM0 RTOS static pool position	√
KM4_MSP_S	0x3000_9000	4KB	KM4 secure Main Stack Pointer	√

RAM & PSRAM Layout

There are 288KB SRAM for KM4 and 96KB SRAM for KM0, which can be used for Power Management Controller (PMC) code and performance-cared text and data. The following figure and table illustrate the RAM layout with PSRAM.

RAM layout (with PSRAM)

RAM layout (with PSRAM)

Item	Start address	Size (KB)	Description	Mandatory
SRAM0	0x2000_0000	40	For ROM BSS, MSP, …	√
KM4 Bootloader	0x3000_A000	24	KM4 secure bootloader, including code and data	√
KM4 IMG3	0x2007_0000	64	KM4 IMG3, can be recycled if IMG3 is not needed	√
KM4 BDRAM	0x2001_0000	288	KM4 BDRAM data, BSS and heap	√
KM0 BDRAM	0x2006_8000	96	KM0 BDRAM data, BSS and heap	√
KM4 PSRAM	0x6000_0000	3220	KM4 PSRAM code, can be empty	√
KM0 PSRAM	0x6032_5000	876	KM0 PSRAM code, can be empty	√
KM4 HEAP EXT	0x6FFF_FFFF	0	If KM4 heap is not enough, it can be used to extend the heap size	x
KM0 HEAP EXT	0x6FFF_FFFF	0	If KM0 heap is not enough, it can be used to extend the heap size	x