Gameboy Development Forum

Discussion about software development for the old-school Gameboys, ranging from the "Gray brick" to Gameboy Color
(Launched in 2008)

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#1 2020-11-17 19:14:19

gkelly
New member
Registered: 2020-11-17
Posts: 1

Holding a Game Boy in reset from the cartridge

I'm working on a cartridge right now that has a very long (~10s currently, but I might be able to cut that in half) startup time for several of the components, including the component that serves the cartridge bus. I've been looking at the /RST signal on the cartridge connector, and wondering if I can hold the system in reset (with a pull-down to GND) and once my system is on its feet and ready to respond to the bus use GPIO to pull that up.

I feel like I've seen some flash carts reset the system, but I'm not sure if they're doing this by faking running the boot ROM by having their own copy that they map in and out during boot.

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#2 2020-11-17 19:21:20

Tauwasser
Member
Registered: 2010-10-23
Posts: 149

Re: Holding a Game Boy in reset from the cartridge

That's what the SRAM battery switch-over chips do: They hold the system in reset until the 5V line is stable enough, switch the current source for the SRAM and then release /RST. The /RST pin is open-drain and can be used for that purpose, so you're good to go. Don't pull it up to 5V or 3V3 by directly connecting the GPIO or possibly through a resistor. Just let it go using an external transistor controlled by your GPIO which defaults to pull the /RST line low.

Just out of curiosity, what takes 10s to boot on your cartridge? Sounds like a bit microcontroller or SoC booting up?

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