ESP32‑S3‑WROOM‑1 (4 MB flash) keeps rebooting: “partition … exceeds flash size” – where can I get a 4 MB build?

[daleka]

Hi everyone!

Board: ESP32‑S3‑WROOM‑1, 4 MB SPI‑flash, no PSRAM
Host: Windows 11, COM3
Tools: Thonny 4.1.4, esptool 4.8.1

=== Problem =============================================================

Right after flashing the board reboots in a loop with

E (31) flash_parts: partition 3 invalid - offset 0x200000 size 0x600000 exceeds flash chip size 0x400000
E (32) boot: Failed to verify partition table

BootROM detects the flash as 4 MB (0x400000), but the partition table
inside the firmware contains an entry that extends to 8 MB
(2 MB offset + 6 MB size).

=== What I have tried ===================================================

• erase_flash (esptool.py erase_flash) → same result.
• Different flash modes (keep, dio, qio) and speeds.
• --flash_size detect and --flash_size 4MB.
• Stable and preview binaries
  – ESP32_GENERIC_S3‑20250415‑v1.25.0.bin
  – ESP32_GENERIC_S3‑20250724‑v1.26.0‑preview.bin
• The very first flash with Flash size → detect actually booted, but then
  gave a PSRAM error (my module has no PSRAM), so I reflashed – since
  then it’s stuck in the “partition … exceeds flash size” loop.

Every flashing session ends with “Hash verified”, yet MCU reboots
immediately afterward.

=== Suspicions ==========================================================

• Current GENERIC_S3 images are apparently built for 8 MB flash.
• I cannot find a separate 4 MB variant (‑4M.bin) on the download page.
• Maybe the only solution is to build MicroPython myself with
  partitions-4MiB.csv.

=== Questions ==========================================================

1. Is there a ready‑made 4 MB .bin for the ESP32‑S3‑WROOM‑1 module?
2. If not – which exact make options are needed to build a firmware
   with a 4 MB partition table?
3. Is it possible to quickly patch an existing 8 MB .bin by replacing the
   partition table CSV, without rebuilding the whole firmware?

Any hints are highly appreciated – thanks in advance! 😊

[scruss]

mp-image-tool-esp32 can resize the partitions on an ESP32 binary image. I've used it to trim down the image to fit a S3 MINI PRO. It has a ESP32-S3FH4R2 with only 4 MB flash

[scruss]

and here's the command to cut down a stock image file:

mp-image-tool-esp32 -f 4M --resize vfs=2M ESP32_GENERIC_S3-20250415-v1.25.0.bin

[daleka]

Hi scruss,

Just tried your suggestion and it works perfectly—thanks a ton!
Flashed the resized image to my 4 MB ESP32‑S3‑WROOM‑1 and it boots straight to the REPL without any partition‑size errors. 💯

Really appreciate the tip!

[projectgus]

Hi @daleka,

Thanks for the comprehensive description of the problem.

Stable and preview binaries
– ESP32_GENERIC_S3‑20250415‑v1.25.0.bin
– ESP32_GENERIC_S3‑20250724‑v1.26.0‑preview.bin

This seems like a limitation with the v1.25 ESP32_GENERIC_S3 build, I double checked and the partition table embedded in ESP32_GENERIC_S3‑20250415‑v1.25.0.bin is indeed for an 8MiB flash. The command @scruss posted can be used to tweak it.

However, we did some work for MicroPython v1.26 to support "4MiB and larger" flash chips from a common partition table and a single binary image. The partition table embedded in ESP32_GENERIC_S3‑20250724‑v1.26.0‑preview.bin is one of this new type - it's built frompartitions-4MiBplus.csv in the source (and I double checked the contents of the binary match).

I don't have a 4MiB flash ESP32-S3 here to check, but if you're able to please do esptool.py erase_flash, then reflash ESP32_GENERIC_S3‑20250724‑v1.26.0‑preview.bin and capture a boot log then that would be very useful for debugging any issue with this new method on 4MiB ESP32-S3.

[daleka]

Hi projectgus,

Thanks for getting back to me. I followed your steps:

Ran esptool.py erase_flash

Flashed ESP32_GENERIC_S3‑20250724‑v1.26.0‑preview.bin

Rebooted the board and captured the full UART boot log.

Boot log:
ESP-ROM:esp32s3-20210327
Build:Mar 27 2021
rst:0x1 (POWERON),boot:0xa (SPI_FAST_FLASH_BOOT)
SPIWP:0xee
mode:DIO, clock div:1
load:0x3fce2820,len:0xe74
load:0x403c8700,len:0x4
load:0x403c8704,len:0xc20
load:0x403cb700,len:0x2f8c
entry 0x403c88ac
E (297) quad_psram: PSRAM ID read error: 0x00ffffff, PSRAM chip not found or not supported, or wrong PSRAM line mode
E (297) esp_psram: PSRAM enabled but initialization failed. Bailing out.
MicroPython v1.26.0-preview.434.g096ff8b9e on 2025-07-24; Generic ESP32S3 module with ESP32S3
Type "help()" for more information.
MicroPython v1.26.0-preview.434.g096ff8b9e on 2025-07-24; Generic ESP32S3 module with ESP32S3

Type "help()" for more information.

So the “4 MiB plus” image boots fine on my ESP32‑S3‑WROOM‑1 with 4 MB SPI‑flash.
The PSRAM error is expected since there’s no PSRAM fitted, and the REPL comes up and works.

Let me know if you’d like me to test anything else—I’m happy to help.

Thanks again!

[projectgus]

Ah great, thanks for checking that! So, as of MicroPython 1.26 (upcoming release, currently in preview builds) an unmodified image will work on a 4MiB ESP32-S3.

[scruss]

Confirming that this image (ESP32_GENERIC_S3-20250724-v1.26.0-preview.434.g096ff8b9e.bin) works as expected on a Wemos S3 MINI PRO which has a ESP32-S3FH4R2 (4MB Flash, 2MB PSRAM).