diff options
| author | Kevin O'Connor <kevin@koconnor.net> | 2008-04-01 21:09:05 -0400 |
|---|---|---|
| committer | Kevin O'Connor <kevin@koconnor.net> | 2008-04-01 21:09:05 -0400 |
| commit | 0bb2a44ea48f65628628db30c3fefbb7297df8dc (patch) | |
| tree | 7592810ad36a06607fee7b97c77b2275a4f1464b /README | |
| parent | 18f368edc5141b55efd11d9ca82e7e6ff5914a14 (diff) | |
Minor enhancements to README file.
Diffstat (limited to 'README')
| -rw-r--r-- | README | 19 |
1 files changed, 12 insertions, 7 deletions
@@ -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: |