Tangential question for HN: what is the absolute lowest-level access one can reasonably expect to get to an old Android phone?
I ask because I'm not clear on the architecture of smartphones, which makes it hard to spot opportunities for creatively hacking them. As I understand it, there are at least two OS-like layers: a "baseband" that IIUC is responsible for controlling the radio hardware, and an OS that sits atop to provide applications/display/touchscreen-controls/etc.
I'm aware of projects like PostmarketOS, but these seem to be a replacement for the OS. Is there any equivalent for the baseband? I have an old OnePlus One and would love to have access to some sort of low-level radio API that would let me generate/modulate/transmit/receive/etc radio signals.
That "firmware" which is being replaced by open equivalent is a GNU/Linux system prepared by Quectel running on the modem itself and providing services like AT command or audio routing daemons. The actual baseband-y stuff is done in Qualcomm's DSPs which stay as closed as ever.
Pinephone modem runs its own OS inside. So if you have a Pinephone, you run two Linux'es at the same time: normal OS and the one on the modem. The core of modem responsible for the actual connections to the towers is closed though AFAIK.
That appears to just be an updated version of the vendor's closed binaries for the modem. It doesn't seem to be open or possible to modify in any meaningful way.
I ask because I'm not clear on the architecture of smartphones, which makes it hard to spot opportunities for creatively hacking them. As I understand it, there are at least two OS-like layers: a "baseband" that IIUC is responsible for controlling the radio hardware, and an OS that sits atop to provide applications/display/touchscreen-controls/etc.
I'm aware of projects like PostmarketOS, but these seem to be a replacement for the OS. Is there any equivalent for the baseband? I have an old OnePlus One and would love to have access to some sort of low-level radio API that would let me generate/modulate/transmit/receive/etc radio signals.