machine: Add Timer class implementation for Linux/Glibc.

This uses POSIX timers, but aspects of signal delivery from them is Glibc
specific.

machine/machine/__init__.py

@@ -0,0 +1 @@
+from .timer import *

machine/machine/timer.py

@@ -0,0 +1,89 @@
+import ffilib
+import uctypes
+import array
+import uos
+import os
+import utime
+from signal import *
+
+libc = ffilib.libc()
+librt = ffilib.open("librt")
+
+CLOCK_REALTIME = 0
+CLOCK_MONOTONIC = 1
+SIGEV_SIGNAL = 0
+
+sigval_t = {
+    "sival_int": uctypes.INT32 | 0,
+    "sival_ptr": (uctypes.PTR | 0, uctypes.UINT8),
+}
+
+sigevent_t = {
+    "sigev_value": (0, sigval_t),
+    "sigev_signo": uctypes.INT32 | 8,
+    "sigev_notify": uctypes.INT32 | 12,
+}
+
+timespec_t = {
+    "tv_sec": uctypes.INT32 | 0,
+    "tv_nsec": uctypes.INT64 | 8,
+}
+
+itimerspec_t = {
+    "it_interval": (0, timespec_t),
+    "it_value": (16, timespec_t),
+}
+
+
+__libc_current_sigrtmin = libc.func("i", "__libc_current_sigrtmin", "")
+SIGRTMIN = __libc_current_sigrtmin()
+
+timer_create_ = librt.func("i", "timer_create", "ipp")
+timer_settime_ = librt.func("i", "timer_settime", "PiPp")
+
+def new(sdesc):
+    buf = bytearray(uctypes.sizeof(sdesc))
+    s = uctypes.struct(uctypes.addressof(buf), sdesc, uctypes.NATIVE)
+    return s
+
+def timer_create(sig_id):
+    sev = new(sigevent_t)
+    #print(sev)
+    sev.sigev_notify = SIGEV_SIGNAL
+    sev.sigev_signo = SIGRTMIN + sig_id
+    timerid = array.array('P', [0])
+    r = timer_create_(CLOCK_MONOTONIC, sev, timerid)
+    os.check_error(r)
+    #print("timerid", hex(timerid[0]))
+    return timerid[0]
+
+def timer_settime(tid, hz):
+    period = 1000000000 // hz
+    new_val = new(itimerspec_t)
+    new_val.it_value.tv_nsec = period
+    new_val.it_interval.tv_nsec = period
+    #print("new_val:", bytes(new_val))
+    old_val = new(itimerspec_t)
+    #print(new_val, old_val)
+    r = timer_settime_(tid, 0, new_val, old_val)
+    os.check_error(r)
+    #print("old_val:", bytes(old_val))
+    #print("timer_settime", r)
+
+
+class Timer:
+
+    def __init__(self, id, freq):
+        self.id = id
+        self.tid = timer_create(id)
+        self.freq = freq
+
+    def callback(self, cb):
+        self.cb = cb
+        timer_settime(self.tid, self.freq)
+        org_sig = signal(SIGRTMIN + self.id, self.handler)
+        #print("Sig %d: %s" % (SIGRTMIN + self.id, org_sig))
+
+    def handler(self, signum):
+        #print('Signal handler called with signal', signum)
+        self.cb(self)