IC: RTL8721Dx RTL8720E RTL8726E RTL8730E

Features

RTL8721DxRTL8720ERTL8726ERTL8730E

• On-chip boot ROM

• Contains the bootloader with In-System Programming (ISP) facility

• Secure boot process using the Ed25519 Cryptographic Algorithm

• Suspend resume process for low power

• Boot from NOR flash

• PSRAM as a memory

Boot Address

RTL8721DxRTL8720ERTL8726ERTL8730E

On reset, the processor loads the PC with the value of the reset vector defined in the vector table, which is fixed by hardware. Both KM4 and KM0 boot from address 0x0000_0000.

CPU	Boot address	Type
KM4	0x0000_0000	KM4 ITCM ROM
KM0	0x0000_0000	KM0 ITCM ROM

Pin Description

RTL8721DxRTL8720ERTL8726ERTL8730E

The SoC supports ISP (In-System Programming) via LOGUART (PB4 / PB5) or USB to download code into Flash. The ISP mode is determined by the state of PB5 when boot.

Boot Mode	PB5 (DOWNLOAD_MODE)	Description
No ISP	HIGH	ISP bypassed. The IC attempts to boot from Flash.
ISP	LOW	The IC enters ISP via LOGUART or USB.

Note

After mass production, a specific eFuse bit can be programmed to permanently disable ISP mode.

Boot Flow

RTL8721DxRTL8720ERTL8726ERTL8730E

After power-up or hardware reset, the hardware will boot the KM4 core at 150MHz. The boot process is handled by the on-chip Boot ROM and is always executed by the KM4 core.

After executing the KM4 bootloader code, the KM4 will initialize the environment for the KM0 core.

1. KM4 boots ROM

2. KM4 ROM checks whether to enter ISP mode

3. KM4 secure boot, ROM verifies bootloader signature (optional)

4. KM4 boots to bootloader

5. KM4 bootloader set the frequency of SoC according to ameba_bootcfg.c

6. KM4 bootloader establishes the non-secure execution environment according to ameba_boot_trustzonecfg.c if TrustZone is enabled

7. KM4 bootloader assists KM0 images loading and signature verification (optional)

SoC boot flow

Boot API

The API BOOT_Reason() is used to obtain the cause of chip boot, and the function prototype is:

u32 BOOT_Reason(void);

The return value of this API will be printed via LOGUART, and the default return value is 0 when the chip is initially powered-on. The return value of re-boot caused by other reasons can be found in the following table. Users can find macro-definitions about return value in the file sysreg_aon.h.

RTL8721DxRTL8720ERTL8726ERTL8730E

Items	Description
Introduction	Get boot reason
Parameter	None
Return	Boot reason. It can be any of the following values or combinations: AON_BIT_RSTF_OCP: Enter deep-sleep mode when OCP happens AON_BIT_RSTF_KM0_SYS: KM0 system reset AON_BIT_RSTF_KM4_SYS: KM4 system reset AON_BIT_RSTF_WDG0: KM0 watchdog reset AON_BIT_RSTF_WDG1: KM4 secure watchdog reset AON_BIT_RSTF_WDG2: KM4 non-secure watchdog reset AON_BIT_RSTF_WARM_KM42PERI: KM4 warm reset AON_BIT_RSTF_WARM_KM02PERI: KM0 warm reset AON_BIT_RSTF_DSLP: Wakeup from deep-sleep mode AON_BIT_RSTF_BOR: BOR Reset