ESP32-S3 8MB Octal PSRAM fails to initialize and resets via RTCWDT

[freimann-dev]

Bug description

When initializing 8MB Octal PSRAM on an ESP32-S3 using Rust (esp-idf-sys), the application crashes immediately during PSRAM / MMU initialization before entering main().

The boot sequence is as follows:

1. Memory access drops mid-log line (d mmu entry)), followed by corrupted UART output.
2. The CPU completely freezes for 2–3 seconds (panic handler cannot run from unreadable Flash).
3. The hardware RTC Watchdog Timer forces a hard reset (rst:0x10 (RTCWDT_RTC_RST)).

Full Serial Output (esp-idf-sys crash)

iurii@acer:~/projects/rs-psram$ cargo run
Blocking waiting for file lock on artifact directory
Compiling rs-psram v0.1.0 (/home/iurii/projects/rs-psram)
Finished dev profile [optimized + debuginfo] target(s) in 11.63s
Running espflash flash --monitor target/xtensa-esp32s3-espidf/debug/rs-psram
[2026-07-22T16:59:15Z INFO ] Serial port: '/dev/ttyACM0'
[2026-07-22T16:59:15Z INFO ] Connecting...
[2026-07-22T16:59:15Z INFO ] Using flash stub
Chip type: esp32s3 (revision v0.2)
Crystal frequency: 40 MHz
Flash size: 16MB
Features: WiFi, BLE, Embedded Flash
MAC address: 44:1b:f6:c9:50:6c
App/part. size: 622,544/16,384,000 bytes, 3.80%
[00:00:01] [========================================] 1/1 0x0 Verifying... OK!
[00:00:00] [========================================] 1/1 0x8000 Verifying... OK!
[00:00:28] [========================================] 19/19 0x10000 Verifying... OK![2026-07-22T16:59:47Z INFO ] Flashing has completed!
Commands:
CTRL+R Reset chip
CTRL+C Exit

ESP-ROM:esp32s3-20210327
Build:Mar 27 2021
rst:0x1 (POWERON),boot:0x2b (SPI_FAST_FLASH_BOOT)
SPIWP:0xee
mode:DIO, clock div:2
load:0x3fce2820,len:0x158c
load:0x403c8700,len:0xd24
load:0x403cb700,len:0x2f34
entry 0x403c8924
I (29) boot: ESP-IDF v5.5.1-838-gd66ebb86d2e 2nd stage bootloader
I (30) boot: compile time Nov 26 2025 12:27:56
I (30) boot: Multicore bootloader
I (31) boot: chip revision: v0.2
I (34) boot: efuse block revision: v1.4
I (38) boot.esp32s3: Boot SPI Speed : 40MHz
I (42) boot.esp32s3: SPI Mode : DIO
I (45) boot.esp32s3: SPI Flash Size : 16MB
I (49) boot: Enabling RNG early entropy source...
I (54) boot: Partition Table:
I (56) boot: ## Label Usage Type ST Offset Length
I (63) boot: 0 nvs WiFi data 01 02 00009000 00006000
I (69) boot: 1 phy_init RF data 01 01 0000f000 00001000
I (76) boot: 2 factory factory app 00 00 00010000 00fa0000
I (82) boot: End of partition table
I (86) esp_image: segment 0: paddr=00010020 vaddr=3c060020 size=2c7a8h (182184) map
I (138) esp_image: segment 1: paddr=0003c7d0 vaddr=3fc91e00 size=030e4h ( 12516) load
I (141) esp_image: segment 2: paddr=0003f8bc vaddr=40374000 size=0075ch ( 1884) load
I (142) esp_image: segment 3: paddr=00040020 vaddr=42000020 size=5a980h (371072) map
I (240) esp_image: segment 4: paddr=0009a9a8 vaddr=4037475c size=0d600h ( 54784) load
I (262) boot: Loaded app from partition at offset 0x10000
I (262) boot: Disabling RNG early entropy source...
I (271) cpu_start: Multicore app
I (272) octal_psram: vendor id : 0x0d (AP)
I (272) octal_psram: dev id : 0x02 (generation 3)
I (272) octal_psram: density : 0x03 (64 Mbit)
I (276) octal_psram: good-die : 0x01 (Pass)
I (281) octal_psram: Latency : 0x01 (Fixed)
I (285) octal_psram: VCC : 0x01 (3V)
I (289) octal_psram: SRF : 0x01 (Fast Refresh)
I (294) octal_psram: BurstType : 0x01 (Hybrid Wrap)
I (299) octal_psram: BurstLen : 0x01 (32 Byte)
I (303) octal_psram: Readlatency : 0x02 (10 cycles@Fixed)
I (309) octal_psram: DriveStrength: 0x00 (1/1)
I (313) esp_psram: Found 8MB PSRAM device
I (317) esp_psram: Speed: 40MHz
D (319) cpu_start: Pro cpu up
D (322) cpu_start: Starting app cpu, entry point is 0x4037606c
0x4037606c - call_start_cpu1
at /home/iurii/projects/rs-psram/.embuild/espressif/esp-idf/v5.2.2/components/esp_system/port/cpu_start.c:183
D (0) cpu_st�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������oting.
ESP-ROM:esp32s3-20210327
Build:Mar 27 2021
rst:0x10 (RTCWDT_RTC_RST),boot:0x2b (SPI_FAST_FLASH_BOOT)
SPIWP:0xee
mode:DIO, clock div:2
load:0x3fce2820,len:0x158c
load:0x403c8700,len:0xd24
load:0x403cb700,len:0x2f34
entry 0x403c8924
I (30) boot: ESP-IDF v5.5.1-838-gd66ebb86d2e 2nd stage bootloader
I (30) boot: compile time Nov 26 2025 12:27:56
I (30) boot: Multicore bootloader
I (32) boot: chip revision: v0.2
I (34) boot: efuse block revision: v1.4
I (38) boot.esp32s3: Boot SPI Speed : 40MHz
I (42) boot.esp32s3: SPI Mode : DIO
I (45) boot.esp32s3: SPI Flash Size : 16MB
I (49) boot: Enabling RNG early entropy source...
I (54) boot: Partition Table:
I (56) boot: ## Label Usage Type ST Offset Length
I (63) boot: 0 nvs WiFi data 01 02 00009000 00006000
I (69) boot: 1 phy_init RF data 01 01 0000f000 00001000
I (76) boot: 2 factory factory app 00 00 00010000 00fa0000
I (82) boot: End of partition table
I (86) esp_image: segment 0: paddr=00010020 vaddr=3c060020 size=2c7a8h (182184) map
I (138) esp_image: segment 1: paddr=0003c7d0 vaddr=3fc91e00 size=030e4h ( 12516) load
I (141) esp_image: segment 2: paddr=0003f8bc vaddr=40374000 size=0075ch ( 1884) load
I (142) esp_image: segment 3: paddr=00040020 vaddr=42000020 size=5a980h (371072) map
I (240) esp_image: segment 4: paddr=0009a9a8 vaddr=4037475c size=0d600h ( 54784) load
I (262) boot: Loaded app from partition at offset 0x10000
I (262) boot: Disabling RNG early entropy source...
I (271) cpu_start: Multicore app
I (272) octal_psram: vendor id : 0x0d (AP)
I (272) octal_psram: dev id : 0x02 (generation 3)
I (272) octal_psram: density : 0x03 (64 Mbit)
I (276) octal_psram: good-die : 0x01 (Pass)
I (281) octal_psram: Latency : 0x01 (Fixed)
I (285) octal_psram: VCC : 0x01 (3V)
I (289) octal_psram: SRF : 0x01 (Fast Refresh)
I (294) octal_psram: BurstType : 0x01 (Hybrid Wrap)
I (299) octal_psram: BurstLen : 0x01 (32 Byte)
I (303) octal_psram: Readlatency : 0x02 (10 cycles@Fixed)
I (309) octal_psram: DriveStrength: 0x00 (1/1)
I (313) esp_psram: Found 8MB PSRAM device
I (317) esp_psram: Speed: 40MHz
D (320) cpu_start: Pro cpu up
D (322) cpu_start: Starting app cpu, entry point is 0x4037606c
0x4037606c - call_start_cpu1
at /home/iurii/projects/rs-psram/.embuild/espressif/esp-idf/v5.2.2/components/esp_system/port/cpu_start.c:183
D (0) cpu_st����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������iurii@acer:~/projects/rs-psram$

• Would you like to work on a fix? [n]

To Reproduce

1. Connect an Freenove ESP32-S3 Wroom board (16MB Flash, 8MB Octal PSRAM).
2. Clone the reproduction repository: rs-psram

Expected behavior

The PSRAM memory test should complete successfully, the 8MB PSRAM pool should be added to the heap allocator, and execution should reach main().
A baseline project using pure ESP-IDF C SDK (https://github.com/i-3/es-psram) with the identical hardware configuration initializes PSRAM without issue.

Click to expand full working C log

Leaving...
Hard resetting via RTS pin...
Executing action: monitor
Running idf_monitor in directory /home/iurii/projects/es-psram
Executing "/home/iurii/.espressif/python_env/idf5.2_py3.10_env/bin/python /home/iurii/.espressif/v5.2.7/esp-idf/tools/idf_monitor.py -p /dev/ttyACM0 -b 115200 --toolchain-prefix xtensa-esp32s3-elf- --target esp32s3 --revision 0 /home/iurii/projects/es-psram/build/es-psram.elf -m '/home/iurii/.espressif/python_env/idf5.2_py3.10_env/bin/python' '/home/iurii/.espressif/v5.2.7/esp-idf/tools/idf.py'"...
--- esp-idf-monitor 1.9.0 on /dev/ttyACM0 115200
--- Quit: Ctrl+] | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H
ESP-ROM:esp32s3-20210327
Build:Mar 27 2021
rst:0x1 (POWERON),boot:0x2b (SPI_FAST_FLASH_BOOT)
SPIWP:0xee
mode:DIO, clock div:1
load:0x3fce3820,len:0x19fc
load:0x403c9700,len:0x4
load:0x403c9704,len:0xe8c
load:0x403cc700,len:0x3154
SHA-256 comparison failed:
Calculated: 0906e3b6faddd899c92766dbec47353b0dfa1bb4819fb1158db80b4d2ad55346
Expected: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
Attempting to boot anyway...
entry 0x403c9940
I (45) boot: ESP-IDF v5.2.7 2nd stage bootloader
I (45) boot: compile time Jul 21 2026 21:58:41
I (45) boot: Multicore bootloader
I (48) boot: chip revision: v0.2
I (52) boot: efuse block revision: v1.4
I (57) qio_mode: Enabling QIO for flash chip MXIC
I (62) boot.esp32s3: Boot SPI Speed : 80MHz
I (67) boot.esp32s3: SPI Mode : QIO
I (72) boot.esp32s3: SPI Flash Size : 16MB
I (76) boot: Enabling RNG early entropy source...
I (82) boot: Partition Table:
I (85) boot: ## Label Usage Type ST Offset Length
I (93) boot: 0 nvs WiFi data 01 02 00009000 00006000
I (100) boot: 1 phy_init RF data 01 01 0000f000 00001000
I (108) boot: 2 factory factory app 00 00 00010000 00100000
I (115) boot: End of partition table
I (120) esp_image: segment 0: paddr=00010020 vaddr=3c020020 size=0a074h ( 41076) map
I (132) esp_image: segment 1: paddr=0001a09c vaddr=3fc92900 size=03040h ( 12352) load
I (138) esp_image: segment 2: paddr=0001d0e4 vaddr=40374000 size=02f34h ( 12084) load
I (147) esp_image: segment 3: paddr=00020020 vaddr=42000020 size=13210h ( 78352) map
I (161) esp_image: segment 4: paddr=00033238 vaddr=40376f34 size=0b904h ( 47364) load
I (174) boot: Loaded app from partition at offset 0x10000
I (175) boot: Disabling RNG early entropy source...
I (186) cpu_start: Multicore app
I (187) octal_psram: vendor id : 0x0d (AP)
I (187) octal_psram: dev id : 0x02 (generation 3)
I (190) octal_psram: density : 0x03 (64 Mbit)
I (195) octal_psram: good-die : 0x01 (Pass)
I (200) octal_psram: Latency : 0x01 (Fixed)
I (206) octal_psram: VCC : 0x01 (3V)
I (211) octal_psram: SRF : 0x01 (Fast Refresh)
I (216) octal_psram: BurstType : 0x01 (Hybrid Wrap)
I (222) octal_psram: BurstLen : 0x01 (32 Byte)
I (228) octal_psram: Readlatency : 0x02 (10 cycles@Fixed)
I (234) octal_psram: DriveStrength: 0x00 (1/1)
I (239) esp_psram: Found 8MB PSRAM device
I (244) esp_psram: Speed: 40MHz
I (979) esp_psram: SPI SRAM memory test OK
I (987) cpu_start: Pro cpu start user code
I (987) cpu_start: cpu freq: 160000000 Hz
I (987) cpu_start: Application information:
I (990) cpu_start: Project name: es-psram
I (995) cpu_start: App version: 1
I (1000) cpu_start: Compile time: Jul 21 2026 21:59:22
I (1006) cpu_start: ELF file SHA256: ea15cee7b...
I (1011) cpu_start: ESP-IDF: v5.2.7
I (1016) cpu_start: Min chip rev: v0.0
I (1021) cpu_start: Max chip rev: v0.99
I (1026) cpu_start: Chip rev: v0.2
I (1031) heap_init: Initializing. RAM available for dynamic allocation:
I (1038) heap_init: At 3FC96250 len 000534C0 (333 KiB): RAM
I (1044) heap_init: At 3FCE9710 len 00005724 (21 KiB): RAM
I (1051) heap_init: At 3FCF0000 len 00008000 (32 KiB): DRAM
I (1057) heap_init: At 600FE010 len 00001FD8 (7 KiB): RTCRAM
I (1063) esp_psram: Adding pool of 8192K of PSRAM memory to heap allocator
I (1071) spi_flash: detected chip: mxic
I (1075) spi_flash: flash io: qio
I (1079) sleep: Configure to isolate all GPIO pins in sleep state
I (1086) sleep: Enable automatic switching of GPIO sleep configuration
I (1094) main_task: Started on CPU0
I (1104) esp_psram: Reserving pool of 32K of internal memory for DMA/internal allocations
I (1104) main_task: Calling app_main()
I (1114) MAIN: =================================
I (1114) MAIN: PSRAM initialized successfully!
I (1124) MAIN: =================================
I (1124) MAIN: PSRAM detected! Size: 8 MB (8388608 bytes)
I (1134) main_task: Returned from app_main()

Done
iurii@acer:~/projects/es-psram$

Environment

• Crate (esp-idf-svc) version: 0.52.1
• ESP-IDF branch or tag: 5.2.2
• Target device (MCU): esp32s3
• OS: Ubuntu 22.04