ppisa commented on code in PR #12081:
URL: https://github.com/apache/nuttx/pull/12081#discussion_r1566426663
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arch/arm/src/samv7/sam_qencoder.c:
##########
@@ -270,11 +316,139 @@ static int sam_reset(struct qe_lowerhalf_s *lower)
static int sam_ioctl(struct qe_lowerhalf_s *lower, int cmd,
unsigned long arg)
{
- /* No ioctl commands supported */
-
+#ifdef CONFIG_SAMV7_QENCODER_ENABLE_GETINDEX
+ switch (cmd)
+ {
+ case QEIOC_GETINDEX:
+ {
+ /* Call the qeindex function */
+
+ sam_qeindex(lower, (struct qe_index_s *) arg);
+ return OK;
+ }
+
+ default:
+ {
+ return -ENOTTY;
+ }
+ }
+#else
return -ENOTTY;
+#endif
}
+#ifdef CONFIG_SAMV7_QENCODER_ENABLE_GETINDEX
+/****************************************************************************
+ * Name: sam_qe_pos_16to32b
+ *
+ * Description:
+ * An inline function performing the extension of current position.
+ * Last reading is saved to priv->last_pos.
+ *
+ ****************************************************************************/
+
+static inline int32_t sam_qe_pos_16to32b(struct qe_lowerhalf_s *lower,
+ uint32_t current_pos)
+{
+ struct sam_lowerhalf_s *priv = (struct sam_lowerhalf_s *) lower;
+
+ uint32_t new_pos = *(volatile uint32_t *) &priv->last_pos;
+ new_pos += (int16_t) (current_pos - new_pos);
+ *(volatile uint32_t *) &priv->last_pos = new_pos;
+
+ return (int32_t) new_pos;
+}
+#endif
+
+#ifdef CONFIG_SAMV7_QENCODER_ENABLE_GETINDEX
+/****************************************************************************
+ * Name: sam_qe_indx_pos_16to32b
+ *
+ * Description:
+ * An inline function performing the extension of the last index position.
+ * Last reading is saved to priv->last_index.
+ *
+ ****************************************************************************/
+
+static inline int32_t sam_qe_indx_pos_16to32b(struct qe_lowerhalf_s *lower,
+ uint32_t current_indx_pos)
+{
+ struct sam_lowerhalf_s *priv = (struct sam_lowerhalf_s *) lower;
+
+ uint32_t new_index = *(volatile uint32_t *) &priv->last_pos;
Review Comment:
The volatile ensures that the compiler loads previous position value exactly
only once from global (shared) location and proceeds both subtraction and
following addition on this single copy which results in extension to 32-bits.
But if compiler decides for some reason to subtract against one value and then
some another thread/process updates shared value and addition is done against
reload updated value then result is incorrect. So we want to ensure that the
value from the global state is fetched exactly once into local copy.
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