Setting GPNVM bits using PyOCD on Microchip SAM MCUs

program_fuses.py

"""Program GPNVM bits on a SAM microcontroller using pyocd

You'll need pyocd installed (`pip install pyocd`)

"""
from pyocd.core.helpers import ConnectHelper
import time

session = ConnectHelper.session_with_chosen_probe()

FCMD_ADDR = 0x400E0A04
FSR_ADDR = 0x400E0A08
FRR_ADDR = 0x400E0A0C
FKEY = 0x5A << 24

SGPB_CMD = 0xB
CGPB_CMD = 0xC
GGPB_CMD = 0xD

TIMEOUT = 3.0

def set_gpnvm(target, bit):
    target.write32(FCMD_ADDR, SGPB_CMD | FKEY | (bit<< 8))
    start = time.time()
    fsr = target.read32(FSR_ADDR)
    while fsr == 0:
        if time.time() - start > TIMEOUT:
            raise RuntimeError("Timeout waiting for flash status")
        fsr = target.read32(FSR_ADDR)

def clear_gpnvm(target, bit):
    target.write32(FCMD_ADDR, CGPB_CMD | FKEY | (bit<< 8))
    start = time.time()
    fsr = target.read32(FSR_ADDR)
    while fsr == 0:
        if time.time() - start > TIMEOUT:
            raise RuntimeError("Timeout waiting for flash status")
        fsr = target.read32(FSR_ADDR)

def read_gpnvm(target):
    target.write32(FCMD_ADDR, GGPB_CMD | FKEY)
    start = time.time()
    fsr = target.read32(FSR_ADDR)
    while fsr == 0:
        if time.time() - start > TIMEOUT:
            raise RuntimeError("Timeout waiting for flash status")
        fsr = target.read32(FSR_ADDR)
    
    return target.read32(FRR_ADDR)


# Simple example to set the BOOTMODE (bit 1) in the GPNVM bits
# On many SAM MCUs (including SAM3X and SAMG family) GPNVM bit 1 is the boot
# mode. Setting it boots straight from flash instead of the built-in BOOT ROM.
with session:
    target = session.board.target

    print(f"Initial value: {read_gpnvm(target)}")
    set_gpnvm(target, 1) # Set the BOOTMODE bit
    print(f"Updated value: {read_gpnvm(target)}")