Padauk is a Taiwanese supplier of ultra-low cost microcontrollers, notorious for the "3 cent MCU". The supplier itself only offers a closed tool chain with a proprietary C-style language. In the mean time, an open sourced and independently created tool-chain, partially based on reverse engineering, became available.
There are still some areas that are not completely understood. One topic is the initial state of the I/O registers. The behavior of the real device is somewhat inconsistent to the datasheet, which may be due to an errata or due to different behavior of the proprietary and open toolchain.
To investigate this behavior in detail on the Padauk PFS173-S16, a small program was used to copy the entire I/O space to the RAM directly after startup. Since no indexed access of the I/O registers is possible, individual instructions had to be generated to copy each address.
After proper initialization of the MCU peripherals, the I/O area back up is dumped via the serial port.
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