ARM — Cortex-A9 PS

The Zynq-7020’s processing system (PS) is a dual-core ARM Cortex-A9 (~867 MHz, 1 GB DDR3). It is the substrate that ties Atari-XT together — not one of the named realms. (“XT” is X + T; the ARM is what makes them run, which is why the name isn’t “XTA”.)

The PS hosts the modern half of the system:

• FreeRTOS and the modern services — the SD-card filesystem and the GEM AES / VDI helpers. USB-HID input arrives from a companion MCU, not an A9 USB stack.
• The desktop and GEM, drawing through the xt-blitter into the DDR3 framebuffer.
• User-provided binaries — once FreeRTOS gains dynamic ELF loading (see Multitasking & executable loading). It will also host the T-realm m68k emulator.

It reaches the PL over AXI: HP ports carry bulk data (DDR3, the framebuffer, and blitter / scan-out traffic) while GP ports carry control and register access (such as the AXI-Lite blitter bridge). The software that runs here is documented under Operating system.