docs: Add info on MODE16/MODESEGMENT compile time flags

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

diff --git a/docs/Memory_Model.md b/docs/Memory_Model.md
index c77fc22c767dfc4a6dfbea21d5ae122ab23d68b6..196b57ba0e12a92c6508d0feeabb9e121d4ef1ac 100644 (file)
--- a/docs/Memory_Model.md
+++ b/docs/Memory_Model.md
@@ -108,6 +108,15 @@ assembled using ".code16gcc". SeaBIOS is careful to use segment
 registers properly so that the same code can run in the different
 16bit modes that it needs to support.
 
+C code mode flags
+=================
+
+Two compile time flags are available to determine the memory model the
+code is intended for: MODE16 and MODESEGMENT. When compiling for the
+16 bit modes, MODE16 is true and MODESEGMENT is true. In 32bit
+segmented mode, MODE16 is false and MODESEGMENT is true. In 32bit flat
+mode both MODE16 and MODESEGMENT are false.
+
 Common memory used at run-time
 ==============================