Comment riscv_set_register, register_write_direct

Fixes #241

Change-Id: Ia199f15106a0bda465d3918d052ddd4d03655031

src/target/riscv/riscv-013.c

@@ -1056,6 +1056,10 @@ static unsigned register_size(struct target *target, unsigned number)
 		return riscv_xlen(target);
 }
 
+/**
+ * Immediately write the new value to the requested register. This mechanism
+ * bypasses any caches.
+ */
 static int register_write_direct(struct target *target, unsigned number,
 		uint64_t value)
 {

src/target/riscv/riscv.c

@@ -1763,6 +1763,10 @@ bool riscv_has_register(struct target *target, int hartid, int regid)
 	return 1;
 }
 
+/**
+ * This function is called when the debug user wants to change the value of a
+ * register. The new value may be cached, and may not be written until the hart
+ * is running again. */
 int riscv_set_register(struct target *target, enum gdb_regno r, riscv_reg_t v)
 {
 	return riscv_set_register_on_hart(target, riscv_current_hartid(target), r, v);