SPI Flash and External SPI RAM Configuration

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This page is a guide for configuring SPI flash and external SPI RAM. Supported frequency and mode combination, error handling are also elaborated.

Terminology

Term

Definition

SPI

Serial Peripheral Interface

MSPI

Memory SPI Peripheral, SPI Peripheral dedicated for memory

SDR

Single Data Transfer Rate (SDR), also known as STR (Single Transfer Rate)

DDR

Double Data Transfer Rate (DDR), also known as DTR (Double Transfer Rate)

line mode

Number of signals used to transfer data in the data phase of SPI transactions. e.g., for 4-bit-mode, the speed of the data phase would be 4 bit per clock cycle.

FxRx

F stands for flash, R stands for PSRAM, x stands for line mode. e.g., F4R4 stands for an ESP32-S3 with Quad flash and Quad PSRAM.

Note

On ESP32-S3, MSPI stands for the SPI0/1. SPI0 and SPI1 share a common SPI bus. The main flash and PSRAM are connected to the MSPI peripheral. CPU accesses them via Cache.

How to Configure Flash and PSRAM

idf.py menuconfig is used to open the configuration menu.

Configure the Flash

The flash related configurations are under Serial flasher config menu.

  1. Flash type used on the board. For Octal flash, select CONFIG_ESPTOOLPY_OCT_FLASH. For Quad flash, uncheck this configuration.

  2. Flash line mode. Select a line mode in CONFIG_ESPTOOLPY_FLASHMODE. The higher the line mode is, the faster the SPI speed is. See terminology above about the line mode.

  3. Flash sample mode. Select a sample mode in CONFIG_ESPTOOLPY_FLASH_SAMPLE_MODE. DDR mode is faster than SDR mode. See terminology above about SDR and DDR mode.

  4. Flash speed. Select a Flash frequency in CONFIG_ESPTOOLPY_FLASHFREQ.

  5. Flash size. Flash size, in megabytes. Select a flash size in CONFIG_ESPTOOLPY_FLASHSIZE.

Configure the PSRAM

To enable PSRAM, please enable the CONFIG_SPIRAM under Component config / Hardware Settings menu. Then all the PSRAM related configurations will be visible under SPI RAM config menu.

  1. PSRAM type used on the board. Select a type in CONFIG_SPIRAM_MODE for Quad or Octal PSRAM.

  2. PSRAM speed. Select a PSRAM frequency in CONFIG_SPIRAM_SPEED.

Note

Configuration 1 of flash and PSRAM should be selected according to your actual hardware.

For the reset of the above configurations:

  • Flash and PSRAM share the same internal clock.

  • Quad flash only supports STR mode. Octal flash may support either/both STR/DTR modes under OPI mode, depending on the flash model and the vendor.

  • Quad PSRAM only supports STR mode, while Octal PSRAM only supports DTR mode.

Therefore, some limitations should be noticed when configuring configuration 2, 3 and 4 of flash, and configuration 2 of PSRAM. Please refer to All Supported Modes and Speeds.

Note

If a board with Octal flash resets before the second-stage bootloader, please refer to Error Handling Chapter.

All Supported Modes and Speeds

Note

For MSPI DDR mode, the data are sampled on both the positive edge and the negative edge. e.g., if a flash is set to 80 MHz and DDR mode, then the final speed of the flash is 160 MHz. This is faster than the flash setting to 120 Mhz and STR mode.

Important

120 MHz DDR mode is an experimental feature. You will only see it when:

With above step, you will find 120 MHz option is visible.

Risks:

If your chip powers on at a certain temperature, then after the temperature increases or decreases over 20 celsius degree, the accesses to/from PSRAM/flash will crash randomly. Flash access crash will lead to program crash.

Note 20 celsius degree is not a totally correct number. This value may changes among chips.

F8R8 Hardware

Group

Flash mode

Group

PSRAM mode

A

120 MHz DDR

A

120 MHz DDR

A

120 MHz SDR

A

B

80 MHz DDR

B

80 MHz DDR

C

80 MHz SDR

C

40 MHz DDR

C

40 MHz DDR

C

C

< 40 MHz

C

D

D

disable

  1. Flash mode in group A works with PSRAM mode in group A/D.

  2. Flash mode in group B/C works with PSRAM mode in group B/C/D.

F4R8 Hardware

Group

Flash mode

Group

PSRAM mode

A

120 MHz SDR

A

120 MHz DDR

B

80 MHz SDR

B

80 MHz DDR

C

40 MHz SDR

C

40 MHz DDR

C

20 MHz SDR

C

D

D

disable

  1. Flash mode in group A works with PSRAM mode in group A/D.

  2. Flash mode in group B/C works with PSRAM mode in group B/C/D.

F4R4 Hardware

Group

Flash mode

Group

PSRAM mode

A

120 MHz

A

120 MHz

B

80 MHz

B

80 MHz

C

40 MHz

C

40 MHz

C

20 MHz

C

D

D

disable

  1. Flash mode in group A works with PSRAM in group A/C/D.

  2. Flash mode in group B works with PSRAM in group B/C/D.

  3. Flash mode in group C works with PSRAM in group A/B/C/D.

Error Handling

  1. If a board with Octal flash resets before the second-stage bootloader:

    ESP-ROM:esp32s3-20210327
    Build:Mar 27 2021
    rst:0x7 (TG0WDT_SYS_RST),boot:0x18 (SPI_FAST_FLASH_BOOT)
    Saved PC:0x400454d5
    SPIWP:0xee
    mode:DOUT, clock div:1
    load:0x3fcd0108,len:0x171c
    ets_loader.c 78
    

    this may mean that the necessary efuses are not correctly burnt. Please check the eFuse bits of the chip using command espefuse.py summary.

    The ROM bootloader relies on an eFuse bit FLASH_TYPE to reset the flash into the default mode (SPI mode). If this bit is not burnt and the flash is working in OPI mode, ROM bootloader may not be able to read from the flash and load the following images.

  2. If you enabled CONFIG_ESPTOOLPY_OCT_FLASH, and there's an error log saying:

    Octal flash option selected, but EFUSE not configured!
    

    this means:

    • either you're using a board with a Quad flash,

    • or you're using a board with an Octal flash, but the eFuse bit FLASH_TYPE isn't burnt. Espressif guarantees this bit is burnt during module manufacturing, but if the module is manufactured by others, this may happen.

Here is a method to burn the eFuse bit:

python3 ./espefuse.py -p /dev/<serial_device> --do-not-confirm burn_efuse FLASH_TYPE 1

Note

This step is irreversible. Please do check if your hardware is actually using an Octal flash.