JumpStart Application Programming Interface (JSAPI) is a middleware API from ImageCraft for accessing MCU peripherals. With JSAPI, it's simple to access the peripherals of the microcontroller without sacrificing the power specific to each vendor's hardware product. It is part of the JumpStart C++ for Cortex installation, and it can be used by licensed users of JumpStart C++ for Cortex without royalties or additional fees.
To take full advantage of JumpStart API, you will need to consult the device family reference manuals and device datasheets from the vendors. For the ST MCUs, the device family reference manuals describe the MCU family's peripherals and the device datasheets describe the specific MCU series' peripheral implementation, including the number of peripheral units, GPIO pin functions, actual alternate function codes, etc.
The JSAPI environment provides a set of objects, e.g. usart1, porta, i2c1, etc., that you can use to access the MCU features using simple-to-use, yet powerful API. It can even coexist with vendor-provided low level libraries if you need to manipulate low level I/O registers to access features not provided by JSAPI.