Can You Use a DS "One Card" (Flashcart) on a DSi?

No. Original DS flashcarts (often called "One Cards" or slot-1 cards like R4, M3 Simply, etc.) do not work on the DSi or DSi XL.

Technical Reasons

• Different Firmware Checks: The DSi introduced RSA-signed header verification; old carts lack valid signatures.
• Hardware Changes: DSi removed the GBA slot and altered the SPI bus timing, breaking legacy cart initialization.
• Blocked in System Menu: Even if a cart boots, the DSi menu hides unlicensed titles.

What Works on DSi/DSi XL

• DSi-Enhanced Flashcarts: Cards labeled "DSi Compatible" (e.g., Acekard 2i, Supercard DSTWO, R4i Gold 3DS+, R4i-SDHC 3DS RTS) with updatable kernels.
• Legit DSiWare / Cartridges: Only Nintendo-signed software runs natively.

If you already own an original DS flashcart, it will work on a DS Phat or DS Lite, but not on any DSi-family or 3DS-family system without a time-warped exploit (not recommended).