PRAC should happen automatically in the background when possible and when it really needs to stop the controller from accessing something while waiting for the bits to refresh it uses the already existing ALERTn signal.
> Panopticon retrofits an existing signal in the DDR specification, called ALERTn, to effectively “trick” the memory controller to pause issuing new DDR commands. DRAM uses ALERTn to signal errors to the memory controller. Upon receiving this signal, the memory controller stops issuing new DRAM commands and instead re-issues the old memory access. By making use of ALERTn, Panopticon requires no modifications to any hardware other than DRAM itself.
(As I understand PRAC uses the same design as Panopticon for this part)
https://stefan.t8k2.com/rh/PRAC/index.html
> Panopticon retrofits an existing signal in the DDR specification, called ALERTn, to effectively “trick” the memory controller to pause issuing new DDR commands. DRAM uses ALERTn to signal errors to the memory controller. Upon receiving this signal, the memory controller stops issuing new DRAM commands and instead re-issues the old memory access. By making use of ALERTn, Panopticon requires no modifications to any hardware other than DRAM itself.
(As I understand PRAC uses the same design as Panopticon for this part)