Added RISC OS support.

RISC OS builds of Python come with a swi module. Who knew?
Documentation is absurdly poor, but I managed. It works even with the
unofficial 2.7 port that guy did for the Raspberry Pi.

TODO.md

@@ -58,17 +58,6 @@ the time of the first reset, last reset, and number of resets), but the Palm OS
 is 2426 pages. I'll find it eventually.
 
 
-## RISC OS
-
-Unless someone gets a Python with `ctypes` working, we may have to write an
-extension and include extensive manual build instructions. I don't imagine
-`distutils` would cope very well.
-
-I'm not even sure the current method would work with `ctypes`; `_swi` could be
-a compiler extension and not part of `CLib`. RISC OS is so painful to work with
-I haven't even checked.
-
-
 ## Symbian
 
 ```cpp

doc/index.rst

@@ -70,7 +70,7 @@ the others on which it is therefore expected to work as well.
 +------------------+--------+--------------------------+---------------------+
 | ReactOS 0.3.14   | ✓      | :func:`_uptime_windows`  |                     |
 +------------------+--------+--------------------------+---------------------+
-| RISC OS 5.19     | ✗ [*]_ | :func:`_uptime_riscos`   | RISC OS in general  |
+| RISC OS 5.19     | ✓      | :func:`_uptime_riscos`   | RISC OS in general  |
 +------------------+--------+--------------------------+---------------------+
 | Syllable Desktop | ✗ [*]_ | :func:`_uptime_syllable` | AtheOS              |
 | 0.6.7            |        |                          |                     |
@@ -84,9 +84,6 @@ the others on which it is therefore expected to work as well.
 | Windows XP SP 3  | ✓      | :func:`_uptime_windows`  |                     |
 +------------------+--------+--------------------------+---------------------+
 
-.. [*] Our current method relies on :mod:`ctypes`, and RISC OS doesn't seem to
-   have a version of Python available that has a working one.
-
 .. [*] Not even the :command:`uptime` that ships with Syllable Desktop is able
    to determine the system uptime on that platform.
 
@@ -231,13 +228,15 @@ uptime
 
 .. function:: _uptime_riscos
 
-   RISC OS-specific uptime. This uses :c:func:`_kernel_swi` to perform the
+   RISC OS-specific uptime. This uses the :mod:`swi` module to perform the
    software interrupt :c:data:`OS_ReadMonotonicTime`, which returns the uptime
    in centiseconds. This will overflow after about eight months on 32-bit
    systems (2.9 billion years on 64-bit). If this can be detected, the function
    will return :const:`None` rather than rely on assumptions regarding signed
    overflow.
 
+   This function does not require a working :mod:`ctypes`.
+
    .. versionadded:: 1.4
 
 .. function:: _uptime_solaris

src/__init__.py

@@ -21,6 +21,12 @@
 import sys
 import time
 
+try:
+    # RISC OS only.
+    import swi
+except ImportError:
+    pass
+
 try:
     from uptime._posix import _uptime_posix
 except ImportError:
@@ -164,28 +170,15 @@ def _uptime_plan9():
 
 def _uptime_riscos():
     """Returns uptime in seconds or None, on RISC OS."""
-    # Apparently the only way to get at the uptime is through a software
-    # interrupt. In C, this is done through _kernel_swi.
     try:
-        libc = ctypes.CDLL('CLib')
-        libc._kernel_swi.argtypes = [ctypes.c_int,
-                                     ctypes.POINTER(ctypes.c_int * 10),
-                                     ctypes.POINTER(ctypes.c_int * 10)]
+        up = swi.swi('OS_ReadMonotonicTime', ';i')
+        if up < 0:
+            # Overflows after about eight months on 32-bit.
+            return None
+        return up / 100.
     except:
         return None
 
-    OS_ReadMonotonicTime = 0x42 # All sources seem to agree.
-    r = (ctypes.c_int * 10)()   # typedef struct {
-                                #     int r[10];
-                                # } _kernel_swi_regs;
-    libc._kernel_swi(OS_ReadMonotonicTime, ctypes.byref(r), ctypes.byref(r))
-
-    if r[0] < 0:
-        # Overflows after about eight months on 32-bit.
-        return None
-    else:
-        return r[0] / 100.
-
 def _uptime_solaris():
     """Returns uptime in seconds or None, on Solaris."""
     global __boottime