3 ms·
A switch wouldn't work on a serial EEPROM or serial Flash chip, you'd need a microcontroller-in-the-middle that proxies or virtualizes the EEPROM and ignores wr
by oakwhiz 8y ago
A switch wouldn't work on a serial EEPROM or serial Flash chip, you'd need a microcontroller-in-the-middle that proxies or virtualizes the EEPROM and ignores writes. This sort of thing would also break partitioned storage, where persistent state and the system image are located on different partitions within the same Flash chip.
- Scoundreller 8y agoI do recall 24 series 8-pin serial EEPROMs having a write enable line as well that could be locked via a switch. Looking quickly on a random manuacturer’s 93 series, I don’t see such a line, BUT, programming operations are blocked when the voltage is below a certain level. A couple diodes on the Voltage line could be put in séries (via switch) to prevent writes unless desired. Of course, if writes are required at some level for normal operation, your chip firewall strategy works much better. The paytv providers actually implemented a flash writeability check (without trIggerinf a write) upon bootup. One of my ideas was to emulate the 24-series eeprom entirely. For the bigger “TSOP” chips, someone devised a high-speed logic gate that was fast enough to allow the check to pass, but still prevent actual writes.
- Scoundreller 8y agoAnd oh ya, a JTAG interface could provide interesting real-time analysis of what’s going on.
- codewritinfool 8y agoDepends on the device. Some do have *WE pins.
- Scoundreller 8y agoAnd some weird ones have a WE pin that only impacts half the memory space. In that case, sub in a chip that blocks it all-or-nothing, but some firmwares may not like that.