Add NAND vs NOR flash memory documentation and Verilog controller implementations

[Copilot]

Addresses issue requesting coverage of NAND vs NOR flash memory. Provides technical comparison documentation and reference controller implementations.

Documentation (Misc/Flash-Memory/README.md)

Comprehensive comparison covering:

• Architecture: Cell structure (parallel vs series), memory organization (random vs page-based)
• Performance: Read/write/erase speeds, access patterns, throughput characteristics
• Economics: Cost per bit (4x difference), density (up to several TB NAND vs 256Mb NOR), power consumption
• Reliability: Endurance cycles by cell type (SLC/MLC/TLC/QLC), ECC requirements, bad block handling
• Use cases: Code execution (NOR) vs mass storage (NAND), with specific application examples
• Implementation: Interface signals, command sequences, timing requirements

Key comparison table:

Feature	NOR Flash	NAND Flash
Read Speed	5-50 ns	25 μs per page
Write Speed	5-10 μs/byte	200-700 μs/page
Interface	Memory-mapped	Command/address/data mux
Execute-in-Place	Yes	No
Cost per Bit	Higher	3-4x cheaper

Controller Implementations

NOR Flash Controller (nor_flash_controller.v):

• Memory-mapped interface with random byte access
• 6-state FSM handling read/write/erase operations
• Bidirectional data bus with proper tristate control

NAND Flash Controller (nand_flash_controller.v):

• Page-based sequential access with 5-cycle addressing
• 17-state FSM for complete operation sequences
• Status register capture with proper signal stabilization timing

// NOR: Direct memory-mapped access
input [ADDR_WIDTH-1:0] cpu_addr;
inout [DATA_WIDTH-1:0] flash_data;
output flash_oe_n, flash_we_n;  // Simple parallel interface

// NAND: Multiplexed command/address/data
inout [7:0] flash_io;
output flash_cle, flash_ale;    // Latch enables for protocol

Both controllers use industry-standard command sequences and are parameterized for flexibility.

Original prompt

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This section details on the original issue you should resolve

<issue_title>NAND vs. NOR flash memory</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes NAND vs. NOR flash memory #26

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