The early mobile phone system PalmOS was ported to Raspberry Pi RP2040

The author shared a demonstration of the running smoothness on the Raspberry Pi microcontroller, and provided detailed relevant documentation. PalmOS started with the Motorola 68k processor and ran from initial development to version 4.x. For version 5, Palm Inc chose to switch to ARM processors because of their higher speed (always a plus). But what to do with all the software? Many PalmOS applications are written for OS 4.x and compiled for the m68k processor. Palm Inc introduces PACE - Palm Application Compatibility Extensions. PACE intercepts OsCall SysAppLaunch (and a few others) and emulates the m68k processor, allowing all older software to run. When an m68k application calls OsCall, PACE will translate the parameters and call ARM Native OsCall. This means that when the application's logic is running in emulation, all OsCall is native ARM and fast. Combined with the fact that PalmOS 4.x devices typically run at 33MHz, and PalmOS 5.x devices typically run at hundreds of frequencies with little to no slowdown, most older apps compiled for PalmOS 4.x run at very good speeds run. It's even good enough for Palm Inc, since most of the built-in apps like calendar and contacts are still m68k apps, not ARM.