VisualHMI RW power-down storage area: Flash lifespan, sector landing sequence, and secure initialization

The RW area is thepower-down save registerof the HMI: addresses 0x0000~0x7FFF, totaling 64KB (32768×2 bytes), based on Flash storage, with a default value of 0xFFFF upon power-on. Data that cannot be lost during power-off, such as parameters, recipes, and operating status, are stored here. However, it has a lifespan and potential pitfalls, and improper use can damage the firmware.

1. RW area characteristics

2. ⚠️ Fatal risk: Excessive erase-writes can corrupt the firmware

The RW area andfirmware area are physically adjacent. Repeated erase-writes to the RW area, if it spreads to the firmware area, will directly damage the device: black screen, no firmware, blue screen. This is a serious issue, not just a scare tactic.

Additionally, Flash is written insector order(lower addresses are written first), and there is aconsistency risk for cross-sector flag bits- if a flag's two bytes fall in different sectors, a power loss during writing may result in half-new and half-old data.

3. Use correct posture

• Address continuous allocation: Place parameters together in one section, don't scatter them everywhere
• set_array batch writing: Write a group at a time, don't set one by one
• Control writing frequency: Only write when the value changes, don't refresh periodically
• Flag bits placed in the same sector: Flags that require atomicity should be placed together
• Perform boundary value checks during startup: Read RW upon power-on to verify validity (magic number 0x55AA)

function on_init()
  -- 上电检查 RW 是否已初始化（魔数 0x55AA）
  if get_uint16(VT_RW, 0x2000) ~= 0x55AA then
    -- 首次上电，写入默认参数
    set_uint16(VT_RW, 0x2000, 0x55AA)   -- 魔数
    set_uint16(VT_RW, 0x2001, 50)       -- 温度上限默认值
    set_uint16(VT_RW, 0x2002, 4800)     -- 波特率默认值
  else
    -- 已初始化，检查参数边界
    local t = get_uint16(VT_RW, 0x2001)
    if t  100 then
      set_uint16(VT_RW, 0x2001, 50)     -- 越界恢复默认
    end
  end
end

Recommend the dual strategy of "same sector flag + parameter boundary check": confirm initialization with magic number, and perform boundary check to prevent dirty data.

Compiled from Guangzhou Dacai Technology VisualHMI development documentation (hmi-doc.gz-dc.com) LUA tutorial "RW Storage", copyright reserved by Dacai Technology.