.. index:: calling-c
 
.. _calling-c:
 
.. Created calling-c.rst: Sun 21 Aug 2022 13:48:57 AEST 
.. Full Path: /home/tp/mecrisp-unofficial-doc/calling-c.rst 
.. Author Copyright 2022 by t.j.porter <techman001@protonmail.com> 
.. Made by /home/tp/projects/scripts/makerst.sh -->/usr/local/bin/makerst 
.. license: MIT, please see COPYING 
 
Calling C
=========

Calling C Functions from Forth and Vice Versa.
----------------------------------------------

Calling C Functions from Forth
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
::
 
 
 Word osDelay from rtos.s
 
 // -----------------------------------------------------------------------------
     Wortbirne Flag_visible, "osDelay"
     @ ( u -- n ) Wait for Timeout (Time Delay).
 /// \param[in]     ticks         \ref CMSIS_RTOS_TimeOutValue "time ticks" value
 /// \return status code that indicates the execution status of the function.
 // osStatus_t osDelay (uint32_t ticks);
 // -----------------------------------------------------------------------------
 rtos_osDelay:
     push    {r0-r3, lr}
     movs    r0, tos     // ticks
     bl  osDelay
     movs    tos, r0
     pop {r0-r3, pc}

If the C function itself calls Forth words the Data Stack Pointer SPS and Top Of Stack TOS registers have to be passed to the Forth words. 

See https://github.com/spyren/Mecrisp-Cube/blob/master/sdcard/man/CallingCFunction.md  which is part of :ref:`Mecrisp Cube<mecrisp-cube>` in my recent :ref:`Unusual Forths<unusual-forths>` page.