4 ms·

> would have its own local power regulation circuits such that a system level voltage reduction wouldn't impact it. How do you know if external voltage is low

> would have its own local power regulation circuits such that a system level voltage reduction wouldn't impact it. How do you know if external voltage is low if you check it against... a voltage derived from it?

thebruce87m 5y ago
Isn’t that what bandgap voltages are for? https://en.m.wikipedia.org/wiki/Bandgap_voltage_reference https://en.m.wikipedia.org/wiki/Bandgap_voltage_reference
joshvm 5y ago
Almost all micros have brown out detection so you can tell if the device undervolts, and typically you can force the device to auto shut down/reset if that condition trips using an onboard programmable fuse. I don't know how much of an attack surface your typical BOD circuit is though. https://microchipdeveloper.com/8avr:bod https://microchipdeveloper.com/8avr:bod
pjc50 5y ago
This is called brownout detection, and it's a common feature even on low-end microcontrollers. As the other commenter says, it's derivable from a bandgap reference. In re "properly secured system": it's a cost-sensitive games console for children, while there's a big incentive against piracy ultimately there's a limit to how much you can defend. And this is the second line of defense, the bootloader having been breached earlier.
- baybal2 5y ago
  Bandgap reference can't tell anything about body bias voltage, unless it itself built on top of insulator
  - pjc50 5y ago
    Could you elaborate? Isn't the substrate usually tied to ground so we can ignore it in modelling? Or are you saying that it could be floated separately to ground in order to attack the chip?
    - baybal2 5y ago
      Yes, and normally it is. I think on every moderately modern CMOS IC, body bias is controlled. > What is body bias? > Body bias is used to dynamically adjust the threshold voltage (Vt) of a CMOS transistor. While CMOS transistors are usually thought of as having three terminal devices, with terminals for the source, gate, and drain, it’s increasingly common to have a fourth terminal connected to the body (substrate). Because the voltage difference between the source voltage (Vs) and body voltage (Vb) affects the Vt, the body can be thought of as a second gate that helps determine how a transistor turns on and off. https://semiengineering.com/body-bias-what-it-is-and-why-you-should-care/ https://semiengineering.com/body-bias-what-it-is-and-why-you...
- floatboth 5y ago
  The whole "games console" context also comes waaaay after the chip was made — it's not a custom for-Nintendo chip! tegra210 was previously used in the Nvidia Shield 2015, then the Google Pixel C (also from 2015) and the Jetson TX1 dev board.

thebruce87m 5y ago

Isn’t that what bandgap voltages are for? https://en.m.wikipedia.org/wiki/Bandgap_voltage_reference https://en.m.wikipedia.org/wiki/Bandgap_voltage_reference

joshvm 5y ago

Almost all micros have brown out detection so you can tell if the device undervolts, and typically you can force the device to auto shut down/reset if that condition trips using an onboard programmable fuse. I don't know how much of an attack surface your typical BOD circuit is though. https://microchipdeveloper.com/8avr:bod https://microchipdeveloper.com/8avr:bod

pjc50 5y ago

This is called brownout detection, and it's a common feature even on low-end microcontrollers. As the other commenter says, it's derivable from a bandgap reference. In re "properly secured system": it's a cost-sensitive games console for children, while there's a big incentive against piracy ultimately there's a limit to how much you can defend. And this is the second line of defense, the bootloader having been breached earlier.

baybal2 5y ago
Bandgap reference can't tell anything about body bias voltage, unless it itself built on top of insulator
- pjc50 5y ago
  Could you elaborate? Isn't the substrate usually tied to ground so we can ignore it in modelling? Or are you saying that it could be floated separately to ground in order to attack the chip?
  - baybal2 5y ago
    Yes, and normally it is. I think on every moderately modern CMOS IC, body bias is controlled. > What is body bias? > Body bias is used to dynamically adjust the threshold voltage (Vt) of a CMOS transistor. While CMOS transistors are usually thought of as having three terminal devices, with terminals for the source, gate, and drain, it’s increasingly common to have a fourth terminal connected to the body (substrate). Because the voltage difference between the source voltage (Vs) and body voltage (Vb) affects the Vt, the body can be thought of as a second gate that helps determine how a transistor turns on and off. https://semiengineering.com/body-bias-what-it-is-and-why-you-should-care/ https://semiengineering.com/body-bias-what-it-is-and-why-you...
floatboth 5y ago
The whole "games console" context also comes waaaay after the chip was made — it's not a custom for-Nintendo chip! tegra210 was previously used in the Nvidia Shield 2015, then the Google Pixel C (also from 2015) and the Jetson TX1 dev board.