MeshOS T-Deck 1.1.6 merged binary has wrong flash size (8MB), causes boot loop on 16MB T-Deck

[NearlCrews]

Summary

The MeshOS-TDeck-1.1.6-merged.bin merged binary has the bootloader flash size set to 8MB, but the LilyGo T-Deck ships with a 16MB flash chip. This causes the second-stage bootloader to crash immediately during flash controller/MMU initialization, resulting in a tight RTC_SW_SYS_RST boot loop with no log output.

Hardware

• Board: LilyGo T-Deck
• Chip: ESP32-S3 (QFN56) revision v0.2
• Flash: 16MB (Manufacturer: 0x46, Device: 0x4018)
• PSRAM: 8MB (AP_3v3)

Symptoms

After flashing MeshOS-TDeck-1.1.6-merged.bin at offset 0x0, the device enters an infinite boot loop. Serial output at 115200 baud shows:

ESP-ROM:esp32s3-20210327
rst:0x3 (RTC_SW_SYS_RST),boot:0x8 (SPI_FAST_FLASH_BOOT)
Saved PC:0x403cdb0a
SPIWP:0xee
mode:DIO, clock div:1
load:0x3fce3808,len:0x4bc
load:0x403c9700,len:0xbd8
load:0x403cc700,len:0x2a0c
entry 0x403c98d0

This repeats indefinitely. The second-stage bootloader never prints any output — it crashes before reaching any log statements.

Root Cause

The bootloader image header in the merged binary has the flash size byte set to 0x3f (8MB, 80MHz, DIO), but the T-Deck's flash chip is 16MB. The bootloader uses this header value to configure the MMU/flash memory mapping. The mismatch causes an immediate crash at PC 0x403cdb0a (within the bootloader's IRAM segment).

Bootloader header (at offset 0x0 in merged binary):

• Flash size: 8MB ← incorrect
• Flash freq: 80MHz
• Flash mode: DIO
• Chip ID: ESP32-S3

App image header (at offset 0x10000 in merged binary):

• Flash size: 16MB ← correct

Workaround

Erase flash and re-flash with an explicit flash size override:

esptool.py --port <PORT> erase_flash
esptool.py --port <PORT> --chip esp32s3 write_flash --flash_size 16MB --flash_mode dio --flash_freq 80m 0x0 MeshOS-TDeck-1.1.6-merged.bin

The key is --flash_size 16MB, which patches the bootloader header byte from 0x3f to 0x4f during flashing.

Suggested Fix

The build configuration for the T-Deck target should set CONFIG_ESPTOOLPY_FLASHSIZE_16MB=y (or equivalent) so the bootloader is compiled with the correct flash size. This would make the merged binary flash correctly without requiring manual size overrides.

Diagnostic Details

• esptool verify-flash confirmed the binary was written correctly (digest matched)
• eFuses show no secure boot or flash encryption enabled
• Partition table, OTA data, and app image are all valid
• The crash is entirely in the bootloader, before the app is loaded