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R36S System Card and Game Card Separation: EmuELEC Dual-Card Setup

Date: 2026-08-07

1. Trigger: The R36S Dual-Card Nightmare

The R36S open-source handheld (RK3326 / Mali-G31 / 640x480 LCD) has two TF slots: right = OS slot, left = game slot. Many players assume “one card for the system, one for games,” but the stock merchant firmware (custom EmuELEC) boots from the right OS card while the left game slot does nothing — games stay crammed on the system card.

Timeline

  1. Merchant 64G card (EmuELEC) in right OS slot: boots fine
  2. Any game card in the left slot: invisible to the system, game library unchanged
  3. Online “EmuELEC dual-card” advice varies: single-card only / need config changes / switch firmware
  4. Tried another “lazy firmware” (ROCKNIX/ArkOS 6.12): completely black screen (backlight on but no image, status LED off); stock system kept working
  5. Returned to stock EmuELEC, dug into its mount logic, and achieved dual-card separation

Goal

  • 32G card = system card (right OS slot, system only)
  • 64G card = game card (left game slot, games only)
  • On boot, the game library automatically comes from the game card

2. Misdiagnoses: Two Traps

Trap 1: “EmuELEC doesn’t support dual cards”?

Wrong. EmuELEC natively supports dual cards; the mount logic is hardcoded in the system:

  • .config/emuelec/configs/emuelec.conf has ee_mount.handler=eemount (C mount handler)
  • System also ships mount_romfs.sh (older Bash) and storage-roms.mount.sample (systemd template)
  • eemount binary literally contains Trying to mount EEROMS to ... and Last hope, mounting LABEL=EEROMS directly

Real cause: the game card must have a vfat partition labeled EEROMS. On boot EmuELEC mounts it via LABEL=EEROMS and points /storage/roms at the game card. A card without partition/label is skipped by eemount — the “no reaction.”

Trap 2: “System card must be copied whole”?

System card migration does have rules, but not simply “dd the whole image”:

  • System card MBR has 3 partitions: P1 EMUELEC (vfat boot, 1G, start sector 32768), P2 STORAGE (ext4, 5G, start 2129920), P3 EEROMS (vfat, games)
  • P1/P2 start sectors and sizes must match the source image exactly (boot config hardcodes boot=UUID=... disk=UUID=...)
  • RK3326 boot chain (idbloader/U-Boot/trust) lives in the 16MB after MBR, before P1 — copying only partitions gives black screen

So: system card = “dd P1/P2 whole + copy bootloader region”; game card = “just one EEROMS-labeled partition.”

3. Source Verification: eemount Dual-Card Mount Logic (Measured)

3.1 Mount config in stock EmuELEC

In system card P2 (STORAGE), .config/emuelec/configs/emuelec.conf:

## Mount handler: eemount (newer, C) or mount_romfs.sh (older, Bash)
#ee_mount.handler=eemount
ee_mount.retry=1

eemount binary (/usr/sbin/eemount) key strings:

Trying to mount EEROMS to ...
Last hope, mounting LABEL=EEROMS directly
Checking if external system directory ... exists and create it if neccessary
Skipped external drive ... mark file ... does not exist

Conclusion: eemount scans external drives, prefers an EEROMS-labeled partition, falls back to LABEL=EEROMS. That’s why the game card needs the EEROMS label.

3.2 System card migration (merchant 64G → 32G)

# Source image partitions (fdisk)
#   P1: 32768, 1G vfat EMUELEC (boot)
#   P2: 2129920, 5G ext4 STORAGE

# Target card repartition (start sectors must match source)
sfdisk /dev/mmcblk0 <<EOF
label: dos
32768, 2097152, c, *
2129920, 10452992, 83
EOF

# dd P1 / P2 whole (UUID preserved in place)
dd if=full_disk_image.img of=/dev/mmcblk0 bs=1M skip=16 seek=16 count=1024
dd if=full_disk_image.img of=/dev/mmcblk0 bs=1M skip=1040 seek=1040 count=5104

# Copy bootloader (16MB after MBR: idbloader/U-Boot/trust)
dd if=full_disk_image.img of=/dev/mmcblk0 bs=512 skip=1 seek=1 count=32767

3.3 Game card (64G)

sfdisk /dev/sde <<EOF
label: dos
, , c
EOF
mkfs.vfat -F 32 -n EEROMS /dev/sde1

mount /dev/sde1 /mnt/gamecard
cp -a /games/{nes,snes,sfc,famicom,genesis,megadrive,ports} /mnt/gamecard/

Measured data (2026-08-07)

  • 32G system card boots alone: battery icon → R36S boot logo → EmuELEC
  • With 64G game card (EEROMS label): All Games = 15928
  • 12 platforms, 13G total: famicom 387M / fds / nes 1.4G / sfc 3.3G / snes 2.5G / genesis 1.3G / megadrive 2.6G / mastersystem 171M / segacd / sega32x / sg-1000 / ports 1.1G
  • e2fsck / fsck.vfat clean, UUID matches source (boot=UUID=0207-1718 disk=UUID=28173377-...)

4. Conclusions: Reusable Approach

Dual-card in three steps

  1. System card (right OS slot): migrate from stock image — P1/P2 start sectors identical, dd whole, copy bootloader (skip=1 seek=1 count=32767); no game partition needed on the system card
  2. Game card (left game slot): single vfat partition + label EEROMS (mkfs.vfat -F 32 -n EEROMS), platform dirs directly at root
  3. Verify: boot system card, shut down, add game card, reboot — library should be the game card’s

Scope

  • R36S / RK3326 handhelds with EmuELEC custom firmware
  • Players wanting OS/game separation and independent game libraries
  • Already have a bootable system card and want to add a second game card

Key order

Check mount label (EEROMS) → then system card UUID/bootloader → only then suspect the system. Measured: EmuELEC dual-card is native; “game card no reaction” is 90% a partition/label issue.

Pitfall list

  • Game card without partition/label → no reaction: mkfs.vfat -F 32 -n EEROMS
  • System card UUID mismatch → system not found: dd whole, never just copy files
  • Missing bootloader region → black screen: copy count=32767 (16MB)
  • Switching to ROCKNIX/ArkOS lazy firmware → black screen on this unit; EmuELEC is most stable

5. Quick Reference

Human developers

sfdisk /dev/sdX <<EOF   # game card: single vfat partition
label: dos
, , c
EOF
mkfs.vfat -F 32 -n EEROMS /dev/sdX1   # label MUST be EEROMS

Conversational AI

Question: “R36S dual-card, game card in left slot no reaction?” Answer: check whether the game card is a vfat partition labeled EEROMS — EmuELEC’s eemount mounts /storage/roms via LABEL=EEROMS; without the label it’s skipped.

Code agents

  • System card: dd if=image of=card bs=1M skip=16 seek=16 count=1024 (P1) + skip=1040 seek=1040 count=5104 (P2) + bs=512 skip=1 seek=1 count=32767 (bootloader); P1/P2 start sectors match source
  • Game card: mkfs.vfat -F 32 -n EEROMS, platform dirs at root
  • Verify: blkid for UUID/label; on device check All Games count (measured 15928)

This article is licensed under Mulan Open Works License Attribution-PatentLicensed, Version 1 (MulanOWL BY-PL v1), or alternatively CC0-1.0 (public domain dedication). Copyright reserved. Attribution required. For enterprise compliance, please retain the original license notice. Original version: https://k4m7v2pz.github.io/en/blog/games/r36s-emuelec-dual-card-separation.html