+/*
+ * BEWARE! Error propagation is important, as are kinds of return values.
+ *
+ * - Raw USB tranport communicates the number of sent or received bytes,
+ * or negative error codes in the external library's(!) range of codes.
+ * - Internal routines at the "sigrok driver level" communicate success
+ * or failure in terms of SR_OK et al error codes.
+ * - Main loop style receive callbacks communicate booleans which arrange
+ * for repeated calls to drive progress during acquisition.
+ *
+ * Careful consideration by maintainers is essential, because all of the
+ * above kinds of values are assignment compatbile from the compiler's
+ * point of view. Implementation errors will go unnoticed at build time.
+ */
+
+static int sigma_read_raw(struct dev_context *devc, void *buf, size_t size)