stmhal: Fix adc.read_timed so buffer store respects element size.

Addresses issue #1154.

stmhal/adc.c

@@ -228,7 +228,8 @@ STATIC mp_obj_t adc_read_timed(mp_obj_t self_in, mp_obj_t buf_in, mp_obj_t freq_
     // This uses the timer in polling mode to do the sampling
     // We could use DMA, but then we can't convert the values correctly for the buffer
     adc_config_channel(self);
-    for (uint index = 0; index < bufinfo.len; index++) {
+    uint nelems = bufinfo.len / typesize;
+    for (uint index = 0; index < nelems; index++) {
         // Wait for the timer to trigger
         while (__HAL_TIM_GET_FLAG(&TIM6_Handle, TIM_FLAG_UPDATE) == RESET) {
         }

tests/pyb/adc.py

@@ -1,10 +1,30 @@
 from pyb import ADC
 from pyb import Pin
 
+pin = Pin('X22', mode=Pin.IN, pull=Pin.PULL_DOWN)
 adc = ADC('X22')
 print(adc)
 
-adc.read()
+# read single sample
+val = adc.read()
+assert val < 500
 
-buf = bytearray(100)
+# read into bytearray
+buf = bytearray(50)
 adc.read_timed(buf, 500)
+print(len(buf))
+for i in buf:
+    assert i < 500
+
+# read into arrays with different element sizes
+import array
+ar = array.array('h', 25 * [0])
+adc.read_timed(ar, 500)
+print(len(ar))
+for i in buf:
+    assert i < 500
+ar = array.array('i', 30 * [0])
+adc.read_timed(ar, 500)
+print(len(ar))
+for i in buf:
+    assert i < 500

tests/pyb/adc.py.exp

@@ -1 +1,4 @@
 <ADC on X22 channel=13>
+50
+25
+30