Magic-1 Microcode File Format

Based on the provided source files, here's the technical information about the Magic-1's microcode format:

Microinstruction Word Format (56 bits)

typedef struct {
    // Control Fields
    unsigned next:8;       // Next microinstruction address
    unsigned latch:4;      // Register latch control
    unsigned lmar:1;       // Latch MAR
    unsigned lmdrlo:1;     // Latch MDR low byte
    unsigned lmdrhi:1;     // Latch MDR high byte
    unsigned emdrlo:1;     // Drive MDR low byte
    unsigned emdrhi:1;     // Drive MDR high byte
    unsigned priv:1;       // Privileged instruction
    unsigned lmode:1;      // Latch mode bit
    unsigned lpaging:1;    // Latch paging enable
    unsigned misc:4;       // Misc control signals
    unsigned e_l:4;        // Left bus enable
    unsigned e_r:2;        // Right bus enable
    unsigned immval:2;     // Immediate value
    unsigned aluop_size:1; // ALU operation size
    unsigned aluop:2;      // ALU operation
    unsigned carry:1;      // Carry control
    unsigned l_size:1;     // Latch size
    unsigned br_sense:1;   // Branch sense
    unsigned user_ptb:1;   // User page table base
    unsigned code_ptb:1;   // Code/data selection
} mcode_rec_t;

Storage Format

1. Physical Storage

• 5 PROMs (512x8 bits each)
• Each PROM contains different fields of the 56-bit word

prom0.hex - MSBs (next field)
prom1.hex - Next control bits
prom2.hex - Middle control bits
prom3.hex - Additional control bits  
prom4.hex - LSBs

2. Memory Organization

#define MICROCODE_WIDTH 56
#define MICROCODE_DEPTH 512

// Bottom 256 locations: Direct opcode mapping
// Upper 256 locations: Microcode sequences

3. File Generation Process

# Generate microcode files from HTML source
./gen_files.pl microcode.htm ./Autogen/

# Files generated:
- mcode.h      # Microinstruction structure definition
- mcode.c      # Initialized microcode array
- prombits.h   # Bit patterns for PROM programming
- mcdefs.h     # Control signal definitions

4. Key Control Fields

// Register selects
#define R_MSW   1   // Machine Status Word
#define R_C     2   // C register
#define R_PC    3   // Program Counter
#define R_DP    4   // Data Pointer
#define R_SP    5   // Stack Pointer
#define R_A     6   // A register
#define R_B     7   // B register
#define R_MDR   8   // Memory Data Register

// ALU Operations
#define OP_IR13 0   // From instruction
#define OP_AND  1   // Logical AND
#define OP_SUB  2   // Subtract  
#define OP_ADD  3   // Add

The microcode is loaded through PROM programmers and provides the fundamental control layer for the Magic-1 CPU.