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fatfs.c: allow bpbSectorsPerCluster == 0 to mean 256

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This should be compatible to Enhanced DR-DOS.

Tested by building a boot image like the following:

nasm ../ldosmbr/oldmbr.asm -o oldmbr.bin
nasm ../ldosboot/boot.asm -D_FAT16=1 -I ../lmacros/ \
 -D_LOAD_NAME="'LDEBUG'" -o boot16.bin
nasm bootimg.asm -I ../lmacros/ -o disk16.img \
 -D_MBR -D_ALIGNDATA -D_BOOTPATCHFILE=boot16.bin \
 -D_MBRPATCHFILE=oldmbr.bin -D_BPE=16 \
 -D_SPI='(_SPC * 5000)' -D_NUMROOT=512 -D_SPC=256 \
 -D_SPF='((_SPI / _SPC + 255) / 256)' \
 -D_PAYLOADFILE=../ldebug/bin/ldebug.com,quit.com,\
::rename,../k256spc/bin/kernel.sys,kernel.sys,\
command.com,::fill,1,32,autoexec.bat

The repos bootimg, ldosboot, ldosmbr, and lmacros are
available at https://hg.pushbx.org/ecm/

The file ldebug.com is a recent bootable lDebug debugger.
The file command.com is a recent FreeCOM. The file quit.com
is assembled with NASM from
https://hg.pushbx.org/ecm/ldebug/file/e6035c05670a/misc/quit.asm

Run like this:

qemu-system-i386 -hda disk16.img -boot order=c -display curses

To the lDebug prompt "-" enter "boot protocol freedos",
then a "q" command. On success, the quit.com command
can be run to quit the qemu VM.

Not yet done:

- initdisk.c:512 uses MAXCLUSTSIZE defined to 128. This is
not difficult to change but it is unclear whether this
should be changed.

- The boot loaders are not yet adjuscted, requiring use of
the ldosboot or lDebug loaders instead.

- A patch for FORMAT (copylefted) version 0.91u is available
from the Enhanced DR-DOS project. Mirrored in the directory at
https://pushbx.org/ecm/download/edrdos/freedos/
This should be easy enough to update to the most recent version.
This commit is contained in:
C. Masloch 2023-01-04 20:45:56 +01:00 committed by Kenneth J Davis
parent 302b002adb
commit 28cd58688a
1 changed files with 7 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
kernel/fatfs.c
View File

@ -1584,13 +1584,17 @@ VOID bpb_to_dpb(bpb FAR * bpbp, REG struct dpb FAR * dpbp)
bpb sbpb;
fmemcpy(&sbpb, bpbp, sizeof(sbpb));
for (shftcnt = 0; (sbpb.bpb_nsector >> shftcnt) > 1; shftcnt++)
;
if (sbpb.bpb_nsector == 0) {
shftcnt = 8;
} else {
for (shftcnt = 0; (sbpb.bpb_nsector >> shftcnt) > 1; shftcnt++)
;
}
dpbp->dpb_shftcnt = shftcnt;
dpbp->dpb_mdb = sbpb.bpb_mdesc;
dpbp->dpb_secsize = sbpb.bpb_nbyte;
dpbp->dpb_clsmask = sbpb.bpb_nsector - 1;
dpbp->dpb_clsmask = (sbpb.bpb_nsector - 1) & 0xFF;
dpbp->dpb_fatstrt = sbpb.bpb_nreserved;
dpbp->dpb_fats = sbpb.bpb_nfat;
dpbp->dpb_dirents = sbpb.bpb_ndirent;