Part 9: Board Bring-Up & Debugging

Bring-Up Strategy

Board bring-up is the systematic process of verifying a newly assembled PCB. Never power on a new board without a plan — a single short circuit can destroy expensive components. Follow a structured checklist from visual inspection to full functional test.

flowchart TD
    A["Visual Inspection"] --> B["Continuity Check"]
    B --> C["Current-Limited
Power-On"]
    C --> D{"Smoke?
Overcurrent?"}
    D -->|Yes| E["Power OFF
Investigate"]
    D -->|No| F["Measure Power Rails"]
    F --> G{"All Rails
Within Spec?"}
    G -->|No| E
    G -->|Yes| H["Flash Firmware
via SWD"]
    H --> I["Verify Clock &
Oscillator"]
    I --> J["Test Peripherals
(UART, I2C, SPI)"]
    J --> K["Full Functional
Test"]
                            

Essential Equipment

Smoke Test

Visual Inspection Checklist

First Power-On Procedure

# First power-on checklist with current monitoring
import time

# Bench power supply settings
VOLTAGE_LIMIT = 5.0    # V — match your input voltage
CURRENT_LIMIT = 0.100  # A — start very low (100mA)

# Expected quiescent currents (no firmware running)
expected_currents = {
    "STM32F411 (sleep)": 0.002,   # ~2mA quiescent
    "LDO (3.3V reg)":   0.005,   # ~5mA quiescent
    "LEDs (off)":        0.000,   # 0mA when off
    "Total expected":    0.010,   # ~10mA quiescent
}

print("FIRST POWER-ON PROCEDURE")
print("=" * 50)
print(f"Step 1: Set bench PSU to {VOLTAGE_LIMIT}V, {CURRENT_LIMIT*1000:.0f}mA limit")
print(f"Step 2: Connect DMM in series to monitor current")
print(f"Step 3: Power ON — observe current immediately")
print()

for component, current in expected_currents.items():
    print(f"  {component:>25}: {current*1000:>6.1f} mA")

print(f"\nStep 4: If current > {CURRENT_LIMIT*1000:.0f}mA → POWER OFF immediately")
print(f"Step 5: If current stable at ~10mA → proceed to rail checks")
print(f"Step 6: Touch IC packages — nothing should be hot")
print(f"\n⚠ If any component is hot, power off and inspect!")

FIRST POWER-ON PROCEDURE
==================================================
Step 1: Set bench PSU to 5.0V, 100mA limit
Step 2: Connect DMM in series to monitor current
Step 3: Power ON — observe current immediately

     STM32F411 (sleep):    2.0 mA
      LDO (3.3V reg):    5.0 mA
          LEDs (off):    0.0 mA
       Total expected:   10.0 mA

Step 4: If current > 100mA → POWER OFF immediately
Step 5: If current stable at ~10mA → proceed to rail checks
Step 6: Touch IC packages — nothing should be hot

⚠ If any component is hot, power off and inspect!

Power Rail Verification

Measuring Each Rail

# Power rail verification log
rails = [
    {"name": "VBUS (USB 5V)",  "expected": 5.00, "tolerance": 0.25, "test_point": "TP1"},
    {"name": "VCC_3V3",        "expected": 3.30, "tolerance": 0.10, "test_point": "TP2"},
    {"name": "VCC_1V8 (core)", "expected": 1.80, "tolerance": 0.05, "test_point": "TP3"},
    {"name": "VREF_ADC",       "expected": 3.30, "tolerance": 0.03, "test_point": "TP4"},
    {"name": "VBAT (backup)",  "expected": 3.00, "tolerance": 0.30, "test_point": "TP5"},
]

print("Power Rail Verification")
print("=" * 75)
print(f"{'Rail':>18} | {'Expected':>9} | {'Tolerance':>10} | {'TP':>5} | {'Status':>8}")
print("-" * 75)

# Simulated measurements (replace with actual readings)
measured = [5.02, 3.28, 1.79, 3.31, 2.98]

for rail, meas in zip(rails, measured):
    exp = rail["expected"]
    tol = rail["tolerance"]
    within = abs(meas - exp) <= tol
    status = "✓ PASS" if within else "✗ FAIL"
    print(f"{rail['name']:>18} | {exp:>7.2f} V | ±{tol:>6.2f} V | {rail['test_point']:>5} | {status:>8}")
    if within:
        print(f"{'':>18}   Measured: {meas:.3f} V (Δ = {abs(meas-exp)*1000:.1f} mV)")

print("\nTip: Measure with scope for AC ripple (DC offset + AC coupling)")

Power Rail Verification
===========================================================================
              Rail |  Expected |  Tolerance |    TP |   Status
---------------------------------------------------------------------------
    VBUS (USB 5V)  |   5.00 V  | ±  0.25 V  |   TP1 |   ✓ PASS
                     Measured: 5.020 V (Δ = 20.0 mV)
         VCC_3V3   |   3.30 V  | ±  0.10 V  |   TP2 |   ✓ PASS
                     Measured: 3.280 V (Δ = 20.0 mV)
  VCC_1V8 (core)   |   1.80 V  | ±  0.05 V  |   TP3 |   ✓ PASS
                     Measured: 1.790 V (Δ = 10.0 mV)
        VREF_ADC   |   3.30 V  | ±  0.03 V  |   TP4 |   ✓ PASS
                     Measured: 3.310 V (Δ = 10.0 mV)
   VBAT (backup)   |   3.00 V  | ±  0.30 V  |   TP5 |   ✓ PASS
                     Measured: 2.980 V (Δ = 20.0 mV)

Tip: Measure with scope for AC ripple (DC offset + AC coupling)

Ripple & Noise Measurement

Firmware Flashing

SWD Connection

# Verify SWD connection with OpenOCD
# Connect ST-Link V2 to board's SWD header
# SWDIO → Pin 2, SWCLK → Pin 4, GND → Pin 3, VCC → Pin 1

# Test connection (STM32F411)
openocd -f interface/stlink.cfg \
        -f target/stm32f4x.cfg \
        -c "init; targets; exit"

# Expected output:
# Info : STLINK V2J37S7 (API v2) VID:PID 0483:3748
# Info : Target voltage: 3.294346
# Info : stm32f4x.cpu: Cortex-M4 r0p1 processor detected
# Info : stm32f4x.cpu: target state: halted

OpenOCD Flash & Debug

# Flash firmware via OpenOCD + GDB
# Step 1: Start OpenOCD server
openocd -f interface/stlink.cfg -f target/stm32f4x.cfg &

# Step 2: Connect with GDB
arm-none-eabi-gdb firmware.elf

# In GDB:
# (gdb) target remote :3333
# (gdb) monitor reset halt
# (gdb) load
# (gdb) monitor reset run

# Alternative: Flash directly with OpenOCD
openocd -f interface/stlink.cfg \
        -f target/stm32f4x.cfg \
        -c "program firmware.bin verify reset exit 0x08000000"

# Using STM32CubeProgrammer CLI
STM32_Programmer_CLI -c port=SWD freq=4000 \
    -w firmware.bin 0x08000000 -v -rst

Debug Instruments

Oscilloscope Techniques

Logic Analyzer Protocol Decode

# Logic analyzer capture analysis — UART decode example
# Using sigrok/PulseView or Saleae Logic

# UART timing calculator
baud_rates = [9600, 115200, 460800, 921600, 1000000]

print("UART Bit Timing Reference")
print("=" * 55)
print(f"{'Baud Rate':>12} | {'Bit Period':>12} | {'Byte Time':>12} | {'1KB Time':>10}")
print("-" * 55)

for baud in baud_rates:
    bit_us = 1e6 / baud               # microseconds per bit
    byte_us = 10 * bit_us             # 10 bits per byte (start + 8 data + stop)
    kb_ms = 1024 * byte_us / 1000     # ms to send 1KB
    print(f"{baud:>12,} | {bit_us:>9.2f} µs | {byte_us:>9.1f} µs | {kb_ms:>7.1f} ms")

print("\nTip: Measure bit period on scope to verify actual baud rate")
print("Tip: Use logic analyzer protocol decoder for I2C/SPI/UART")

UART Bit Timing Reference
=======================================================
   Baud Rate |   Bit Period |    Byte Time |   1KB Time
-------------------------------------------------------
       9,600 |   104.17 µs  |   1041.7 µs  |  1066.7 ms
     115,200 |     8.68 µs  |     86.8 µs  |    88.9 ms
     460,800 |     2.17 µs  |     21.7 µs  |    22.2 ms
     921,600 |     1.09 µs  |     10.9 µs  |    11.1 ms
   1,000,000 |     1.00 µs  |     10.0 µs  |    10.2 ms

Tip: Measure bit period on scope to verify actual baud rate
Tip: Use logic analyzer protocol decoder for I2C/SPI/UART

Multimeter Diagnostics

Bring-Up Log Tool

Generate a structured bring-up checklist and test log for your board, documenting each step from visual inspection through functional testing.

Exercises

Conclusion & Next Steps

Board bring-up is where your design meets reality. By following a systematic approach — visual inspection, current-limited power-on, rail verification, firmware flash, and peripheral testing — you’ll catch issues early and build confidence in your hardware. Document everything in your bring-up log for future revisions.