Minor enhancements to README file.

diff --git a/README b/README
index 0ca5f1b469063817315cd406c67153a57337aa4a..dc0a725d79e09267beb31ec2e6037e0bf8567994 100644 (file)
--- a/README
+++ b/README
@@ -51,10 +51,8 @@ Overview of files:
 
 The src/ directory contains the bios source code.  Several of the
 files are compiled twice - once for 16bit mode and once for 32bit
-mode.  The gcc compile option '-fwhole-program' is used to remove code
-that is not needed for a particular mode.  (In the code, one can use
-the macros 'VISIBLE16' and 'VISIBLE32' to instruct a symbol to be
-outputted in 16bit and 32bit mode respectively.)
+mode.  (The gcc compile option '-fwhole-program' is used to remove
+code that is not needed for a particular mode.)
 
 The tools/ directory contains helper utilities for manipulating and
 building the final rom.
@@ -67,7 +65,9 @@ Build overview:
 
 The 16bit code is compiled via gcc to assembler (file out/blob.16.s).
 The gcc "-fwhole-program" option is used to optimize the process so
-that gcc can efficiently compile and discard unneeded code.
+that gcc can efficiently compile and discard unneeded code.  (In the
+code, one can use the macros 'VISIBLE16' and 'VISIBLE32' to instruct a
+symbol to be outputted in 16bit and 32bit mode respectively.)
 
 This resulting assembler code is pulled into romlayout.S.  The gas
 option ".code16gcc" is used prior to including the gcc generated
@@ -133,8 +133,7 @@ much stack space can break old DOS applications.
 
 There does not appear to be explicit documentation on the minimum
 stack space available for bios calls.  However, Freedos has been
-observed to call into the bios with less than 150 bytes of stack space
-available.
+observed to call into the bios with less than 150 bytes available.
 
 Note that the post code and boot code (irq 18/19) do not have a stack
 limitation because the entry points for these functions reset the
@@ -147,6 +146,12 @@ to functions often helps, sometimes reordering variable declarations
 helps, inlining of functions can sometimes help, and passing of packed
 structures can also help.
 
+Some useful stats: the overhead for the entry to a bios handler that
+takes a 'struct bregs' is 38 bytes of stack space (6 bytes from
+interrupt insn, 28 bytes to store registers, and 4 bytes for call
+insn).  An entry to an ISR handler without args takes 30 bytes (6 + 20
++ 4).
+
 
 Debugging the bios: