5 ms·
One of the best ways is to have a dedicated "Chip Enable" pin on the camera module. You then connect an LED to the state of this pin and when the Chip Enable p
by proee 13y ago
One of the best ways is to have a dedicated "Chip Enable" pin on the camera module. You then connect an LED to the state of this pin and when the Chip Enable pin is "Hight" the LED is turned on. However, there needs to be additional circuitry (an extra pin) and some work to ensure proper voltage levels are met for both the pin and the LED (extra cost).
Another option is to enable the LED when power is turned onto the module.
- esmi 13y agoLook at figure 2 in the attached research paper. You'll find this is exactly how this model of iSight camera works. This interlock failed because the Micron sensor Apple used had software straps that could be reconfigured to have the sensor ignore its enable pin.
- lawnchair_larry 13y agoWhat is a software strap? Tried to google what that is and how it works, but I don't see much. Is it known by another term?
- userbinator 13y agoconfiguration.
- lawnchair_larry 13y agoNot really what I'm looking for.
- shabble 13y agoIt's increasingly common in modern ICs (SoCs and microcontrollers especially) to have only the minimum required connections be permanently assigned to physical pins. The rest of the pins are connected to some routing logic which in turn connects to the various chip internal signals. This is great in board design because you can often simplify PCB routing by reassigning pins as you need them for your layout, rather than other other way round. This is usually done at runtime, typically a bit of code that happens after the reset vector that puts the various config values into the appropriate registers that set up this routing and other customisable options. In the case here, it's those other options that are the issue. From the paper, Part IV(A): > The Micron image sensor has a 16 bit configuration register, RESET (which is distinct from the #RESET power on reset signal). RESET is addressable from the I2C interface at address 0x0D in register page 0 And the hack involves setting that configuration register to unexpected values to enable functionality that bypasses the LED display circuit: > Bit 7. Prevent STANDBY from affecting entry to or exit from the low-power state if set. > Bit 6. Prevent STANDBY from contributing to output enable control if set. (where STANDBY is the signal/pin to which the LED is connected) So the controller assumes that the physical STANDBY pin will always accurately reflect/control the state of the sensor, which is not necessarily the case if it's been disabled by re-configuration.
- lawnchair_larry 13y agoThanks, that's informative.