# Volume XXVII: Addendum 1

Subject: Deprecation of Legacy Memory Maps, Dual-Switch Topology, & CD_READY Emulation

Status: DRAFT (Pending RAM Sandbox Fuzzer Verification)

CRITICAL REVISION: The memory map outlined in the original Volume XXVII (referencing `0x9000A040`) is deprecated. Analysis of the firmware boot sector confirms the Panasonic MN103S Special Function Registers (SFRs) are mapped to the `0x03XX` address space.

## 1. The Dual-Switch Tray Topology

Contrary to standard slimline PC drive architecture, the GCC-4241N utilizes a discrete dual-switch system for tray state, multiplexed across separate GPIO ports rather than consolidated on a single register.

- Tray Closed (Back Switch): Routed to Pin 184 / 173. This maps logically to `P13` (Port 1, Bit 3).
- Tray Open (Front Switch): Routed to Pin 192 / 181. This maps logically to `NTRYCL / MONI7`.

Because the Tray Open switch is hardware-tied to an external interrupt pin (`MONI7`), polling loops are unnecessary. The processor will natively vector to the ISR when the tray reaches maximum ejection.

## 2. CD_READY (Pin 6) Emulation Strategy

The Xbox SMC (System Management Controller) expects a logic-low 0V signal on Pin 6 (`CD_READY`) when media is initialized. Using internal drive analog signals such as `MONI0` (Focus OK) or `MONI1` (Spindle Lock) is unsafe; these signals drop during layer transitions or RPM changes, which will trigger an Xbox Error 11/12 hardware crash.

### The Software-Driven Solution

To provide a debounced, rock-solid signal to the Xbox, `CD_READY` will be driven entirely via software logic tied to the Media Authorized Flag.

1. Identify a physically accessible, unused GPIO pad on the MN103S processor (e.g., a zeroed pin on Port 2 or Port 3).
2. Connect Pin 6 of the Xbox yellow cable directly to this pad.
3. Modify the RAM Cave Hook (`0x40008B00`) to drive this GPIO pad Low (0V) when flag `0x2CC` is set, and High (3.3V) when the tray interrupt clears the flag.

## 3. Pending Fuzzer Verification

The final logical memory addresses for Port 0 (LED), Port 1 (Tray Closed), and the unused CD_READY target pad are currently narrowed to the `0x0310 - 0x0374` initialization matrix. A "Walking Bit" assembly fuzzer will be injected via the tethered stub loader to physically toggle the hardware and confirm the exact SFR mapping before finalizing Volume XXVIII.