regtools: update xml format documentation

Change-Id: I7e293532983f350a6f7cd9c7bc2bc6633c8fd3f2
Reviewed-on: http://gerrit.rockbox.org/671
Reviewed-by: Amaury Pouly <amaury.pouly@gmail.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/utils/regtools/desc/XML.txt b/utils/regtools/desc/XML.txt
index 15164a43b9..a90f875f66 100644
--- a/utils/regtools/desc/XML.txt
+++ b/utils/regtools/desc/XML.txt
@@ -100,6 +100,8 @@ In the special case where the addresses of the register follow a pattern, an
 explicit formula can be described as part of the format. There is no specific
 requirement on the formula except that the register addresses be indexed by
 a variable "n" which range from 0 to N-1 where N is the number of address.
+The formula is not used for anything except header generation where it is
+handy to have a formula rather a long list of conditionals.
 The following properties are defined:
 - "string" (mandatory,string): the equation describing the addresses.
 
@@ -130,4 +132,4 @@ Each value is enclosed in a "value" tag. The following properties are defined:
 
 Example:
 <value name="DIV_BY_1" value="0x0" />
-<value name="DIV_BY_2" value="0x1" />
\ No newline at end of file
+<value name="DIV_BY_2" value="0x1" />