added example file calculating clkdiv-register in mp

Author: rze

v10_prototype_version_2/20220109/test_03_calc_register.py

@@ -0,0 +1,80 @@
+#https://forums.raspberrypi.com/viewtopic.php?p=1985859#p1984172
+#Changing frequency of SM while running
+
+#https://datasheets.raspberrypi.com/rp2040/rp2040-datasheet.pdf
+# see chapter 4.9.6. List of Registers
+#Clock divisor register for state machine N
+#Frequency = clock freq / (CLKDIV_INT + CLKDIV_FRAC / 256)
+
+#31:16 INT - Effective frequency is sysclk/(int + frac/256). Value of 0 is interpreted as 65536. If INT is 0, FRAC must also be 0
+#15:8 FRAC - Fractional part of clock divisor
+#7:0 Reserved
+
+import rp2
+from machine import freq, mem32, Pin
+from time import sleep
+
+def sm_div_calc(target_f):
+    if target_f < 0:
+        div = 256
+    elif target_f == 0:
+        # Special case: set clkdiv to 0.
+        div = 0
+    else:
+        div = freq() * 256 // target_f
+        if div <= 256 or div >= 16777216:
+            raise ValueError("freq out of range")
+    return div << 8
+
+@rp2.asm_pio(set_init=rp2.PIO.OUT_LOW)
+
+def signal():
+    wrap_target()
+    nop()
+    wrap()
+
+def sm_div_ref(target_f):
+    sm0 = rp2.StateMachine(0, signal, freq=target_f, set_base=Pin(26))
+    SM0_CLKDIV = 0x50200000 + 0x0c8
+    # convert to signed int value to unsigned int value
+    if (mem32[SM0_CLKDIV]<0):
+        return mem32[SM0_CLKDIV] + 2**32
+    else:
+        return mem32[SM0_CLKDIV]
+
+print("freq():", freq())
+
+# check if same results for example 2000 are calculated
+tf = 2000
+
+#x =  0b10000000_00000000_00000010_00000000
+x = sm_div_ref(tf)
+im = 0b11111111_11111111_00000000_00000000
+fm = 0b00000000_00000000_11111111_00000000
+
+i = (x&im)>>16
+f = (x&fm)>>8
+cf = freq() / (i + f / 256)
+ 
+print("sm()", type(x), x, bin(x), i, f , cf, tf)
+
+#using horuable's function to calc clock divider
+
+div = sm_div_calc(tf)
+
+i = (div&im)>>16
+f = (div&fm)>>8
+print("python",type(div), div, bin(div), i, f , cf, tf)
+
+
+
+assert sm_div_ref(2000) ^ sm_div_calc(2000) == 0, "register values are different for freq 2000"
+
+for f in [2000, 23413, 213123213, 123123,1000, 12323]:
+    try:
+        assert sm_div_ref(f) ^ sm_div_calc(f) == 0, "register values are different for freq "+str(f)
+    except ValueError as e:
+        print(e, "at frequency", str(f))
+        
+
+