I'm trying to understand bus-mastered dma (ide) for a long time but I
clearly don't understand what is
going on. I first compile support into my kernel by selecting:
[*] Intel PIIX/PIIX3/PIIX4 (Triton 430FX/HX/VX/TX, 440FX) DMA support
I then added the following code to my rc.local initialization script:
# Added by Scott Gray on 9/5/97
# hdparm used to set transfer mode to
# multiword DMA mode2
#
# -d1: enable the "using_dma" flag
# -X34: ensure the drive is programmed for DMA mode 2
if [ -f /sbin/hdparm ]; then
echo "Setting hda transfer mode to DMA mode2"
/sbin/hdparm -d1 -X34 /dev/hda
echo "Setting hdb transfer mode to DMA mode2"
/sbin/hdparm -d1 -X34 /dev/hdb
fi
# A message indicating success/failure is generated
# and sent to STDOUT at boot-up.
When I enter the command: "hdparm -i" the follow output is generated:
/dev/hda:
multcount = 16 (on)
I/O support = 1 (32-bit)
unmaskirq = 0 (off)
using_dma = 1 (on)
keepsettings = 0 (off)
nowerr = 0 (off)
readonly = 0 (off)
readahead = 8 (on)
geometry = 622/255/63, sectors = 10003456, start = 0
However, when cat /proc/dma I get:
1: SoundBlaster8
4: cascade
5: SoundBlaster16
I believe the DMA BusMastering is probably working but I would like to
understand a little more about
what is going on. Shouldn't a channel be allocated for the ide drive?
Or does this form of DMA bypass
the DMA controller found on the main board. If yes then does this mean
that the DMA controller is
actually on the drive itself? Also when I cat /proc/ioports I get the
following:
0000-001f : dma1
0020-003f : pic1
0040-005f : timer
0060-006f : keyboard
0070-007f : rtc
0080-008f : dma page reg
00a0-00bf : pic2
00c0-00df : dma2
00f0-00ff : fpu
0170-0177 : ide1
01f0-01f7 : ide0
0220-022f : soundblaster
02f8-02ff : serial(auto)
0300-031f : NE2000
0330-0333 : SB MIDI
0376-0376 : ide1
0388-038b : OPL3/OPL2
03c0-03df : vga+
03f0-03f5 : floppy
03f6-03f6 : ide0
03f7-03f7 : floppy DIR
03f8-03ff : serial(auto)
ffa0-ffa7 : IDE DMA <--- What is
this?
ffa8-ffaf : IDE DMA <--- What is
this?
As you can see, I pretty confused but I think if someone who know could
expain this to me I'm not that far away from understanding.
Thanks,
Scott Gray :)
PS: I'm interested in learning more about device drivers in particular
"block device drivers." Could
anyone recommend a book or some web resource. I was hoping to find
something that talked about the
big picture "in otherwords the basic things that need to be done"
before diving into the kernel source
code.
My drive info is as follows:
/dev/hda:
Model=Maxtor 85120A8, FwRev=AA8Z2225, SerialNo=C804RA6A
Config={ Fixed }
RawCHS=9924/16/63, TrkSize=0, SectSize=0, ECCbytes=20
BuffType=3(DualPortCache), BuffSize=256kB, MaxMultSect=16, MultSect=16
DblWordIO=no, maxPIO=2(fast), DMA=yes, maxDMA=2(fast)
CurCHS=9924/16/63, CurSects=10003392, LBA=yes, LBAsects=10003456
tDMA={min:120,rec:120}, DMA modes: mword0 mword1 mword2
IORDY=on/off, tPIO={min:120,w/IORDY:120}, PIO modes: mode3 mode4