Detailed explanation of the power on process of lattice FPGA

 Here's a detailed technical breakdown of the power-on process for Lattice FPGAs (using iCE40, ECP5, or MachXO families as reference):

Lattice FPGA Power-On Sequence

The boot process involves multiple hardware and firmware-controlled stages:

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1. Power Rail Stabilization

• Required Voltage Rails (typical):

  • Core Voltage (VCC): 1.2V (ECP5) / 1.0V (iCE40)

  • I/O Voltage (VCCIO): 1.8V/2.5V/3.3V (bank-dependent)

  • Auxiliary Voltage (VCCAUX): 2.5V/3.3V (for PLLs, configuration logic)

• Power Sequencing:

  • Option 1: Monolithic ramp (all rails together)

  • Option 2: Staggered (VCCAUX → VCC → VCCIO)

  • Critical: Must meet datasheet timing (e.g., ECP5 requires VCC within 50ms of VCCAUX)

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2. Reset and Configuration Phase

A. Power-On Reset (POR) Circuit

• Internal POR circuit monitors:

  • All voltage rails

  • Clock stability (if external oscillator used)

• POR Timeout: Typically 100-300ms (device-specific)

• Reset States:

  • Cold Reset: Full reconfiguration

  • Warm Reset: Partial reconfiguration (if supported)

B. Configuration Mode Selection

• Sampled at dedicated MODE[2:0] pins:

  Mode	Protocol	Typical Use
  SPI	Serial Flash	Standalone boot
  JTAG	IEEE 1149.1	Debug/programming
  I2C	Slave	Host-controlled
  Parallel	8/16-bit bus	Legacy systems

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3. Bitstream Loading

A. Non-Volatile (Flash-Based) FPGAs (e.g., MachXO2/3)

1. Internal Boot ROM executes

2. Reads embedded Flash (NVM) for configuration

3. Optional AES-256 decryption (if enabled)

4. CRC verification (aborts on failure)

B. Volatile FPGAs (e.g., ECP5, iCE40)

1. External Memory Interface activates:

   • SPI Flash (most common)

   • Lattice Wishbone or Slave Parallel modes

2. Bitstream phases:

   • Header: Checks device compatibility (IDCODE check)

   • Payload: Configuration data + optional compression

   • Termination: CRC32 validation

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4. Initialization and Startup

A. Clock Tree Activation

• Primary clock selection (external/internal)

• PLL lock wait (if used) - typically 1-10ms

• Clock monitoring circuits enable

B. I/O Bring-Up Sequence

1. Bank voltage stabilization

2. Pin states transition:

   • Configuration pins release from high-Z

   • User I/O assumes default states (per bitstream)

3. Dedicated pins (like DONE, INITN) assert:

   • INITN: Low during config, high on success

   • DONE: Final handshake signal

C. Functional Startup

• GR (Global Reset) release

• User logic begins operation

• Optional POST (Power-On Self Test) if implemented

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5. Error Handling

• Common Failure Modes:

  Symptom	Likely Cause	Debug Steps
  Stuck in INITN	Bitstream CRC error	Verify flash contents
  DONE low	Power sequencing failure	Check rail timings
  Intermittent ops	Clock instability	Probe PLL lock status

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6. Timing Diagram (Typical)

Time        | 0ms      50ms      100ms     150ms     200ms
--------------------------------------------------------------------
VCCAUX      | __/¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
VCC         | ____/¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
POR         | ____________/¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
CONFIG      | __________________/¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
DONE        | ______________________________________/¯¯¯¯¯¯¯
User I/O    | __________________________________________/¯¯¯

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7. Design Considerations

1. Power Sequencing:

   • Use Lattice's recommended PMICs (e.g., XPOWER series)

   • Monitor with voltage supervisors (e.g., TPS3839)

2. Configuration Reliability:

   • Implement dual-boot (MachXO3D feature)

   • Use golden fallback images

3. Signal Integrity:

   • Keep configuration traces < 50mm (SPI clock)

   • Add series termination for > 25MHz clocks

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Debugging Tips

• Oscilloscope Checks:

  • Probe all power rails for noise (<5% ripple)

  • Verify INITN/DONE timing

• Lattice Diamond/Primary Tools:

  tcl

  
  

  # Check bitstream header
  report_device -file device_check.rpt
  # Verify SPI flash connection
  verify_config -interface SPI -file design.bit