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John Fieber 1995-11-01 16:40:14 +00:00
parent a19095538b
commit f2248e4c5b
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/branches/RELENG_2_1_0/; revision=141
1 changed files with 15 additions and 15 deletions

30
handbook/dma.sgml
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@ -1,4 +1,4 @@
<!-- $Id: dma.sgml,v 1.1.2.1 1995-10-30 15:23:53 jfieber Exp $ -->
<!-- $Id: dma.sgml,v 1.1.2.2 1995-11-01 16:40:14 jfieber Exp $ -->
<!-- The FreeBSD Documentation Project -->
<!--
@ -14,7 +14,7 @@
<p><em>Copyright &copy; 1995 &a.uhclem;, All Rights Reserved.<newline>
18 October 1995.</em>
<!-- Version 1(1) -->
<!-- Version 1(2) -->
Direct Memory Access (DMA) is a method of allowing data to
be moved from one location to another in a computer without
@ -40,7 +40,7 @@
the way the second controller is wired into the system.
The 8237 has two electrical signals for each channel, named
DRQ and -DACK. There are additional signals that with the
DRQ and -DACK. There are additional signals with the
names HRQ (Hold Request), HLDA (Hold Acknowledge), -EOP
(End of Process), and the bus control signals -MEMR (Memory
Read), -MEMW (Memory Write), -IOR (I/O Read), and -IOW (I/O
@ -78,8 +78,8 @@
The DMA controller will note that the DRQ2 signal is asserted.
The DMA controller will then make sure that DMA channel 2
has been programmed and is enabled. The DMA controller
also makes sure none of the other DMA channels is active
or has a higher priority. Once these checks are
also makes sure that none of the other DMA channels are active
or have a higher priority. Once these checks are
complete, the DMA asks the CPU to release the bus so that
the DMA may use the bus. The DMA requests the bus by
asserting the HRQ signal which goes to the CPU.
@ -145,7 +145,7 @@
incremented and the counter that shows how many bytes are
to be transferred is decremented.
When the counter reaches zero, the asserts the EOP
When the counter reaches zero, the DMA asserts the EOP
signal, which indicates that the counter has reached zero
and no more data will be transferred until the DMA
controller is reprogrammed by the CPU. This event is
@ -208,7 +208,7 @@
span a 64K physical boundary. If the DMA accesses memory
location 0xffff, the DMA will then increment the address
register and it will access the next byte at 0x0000, not
0x10000. The results of this are probably not intended.
0x10000. The results of letting this happen are probably not intended.
<quote><em>Note:</em> ``Physical'' 64K boundaries should
not be confused with 8086-mode 64K ``Segments'', which
@ -268,12 +268,12 @@
The difference between Block and Demand is the once a
Block transfer is started, it runs until the transfer
count reaches zero. DRQ only needs to be asserted
until -DACK is asserted. Demand mode will transfer
until -DACK is asserted. Demand Mode will transfer
one more bytes until DRQ is de-asserted, then when
DRQ is asserted later, the transfer resumes where it
was suspended.
Older hard disk controllers used Demand mode until
Older hard disk controllers used Demand Mode until
CPU speeds increased to the point that it was more
efficient to read the data using the CPU.
@ -429,8 +429,8 @@
DMA Command Registers
<verb>
0x10 write Command register
0x10 read Status register
0x10 write Command Register
0x10 read Status Register
0x12 write Request Register
0x12 read -
0x14 write Single Mask Register Bit
@ -440,7 +440,7 @@ DMA Command Registers
0x18 write Clear LSB/MSB Flip-Flop
0x18 read -
0x1a write Master Clear/Reset
0x1a read Temporary register
0x1a read Temporary Register
0x1c write Clear Mask Register
0x1c read -
0x1e write Write All Mask Register Bits
@ -476,8 +476,8 @@ DMA Command Registers
DMA Command Registers
<verb>
0xd0 write Command register
0xd0 read Status register
0xd0 write Command Register
0xd0 read Status Register
0xd2 write Request Register
0xd2 read -
0xd4 write Single Mask Register Bit
@ -487,7 +487,7 @@ DMA Command Registers
0xd8 write Clear LSB/MSB Flip-Flop
0xd8 read -
0xda write Master Clear/Reset
0xda read Temporary register
0xda read Temporary Register
0xdc write Clear Mask Register
0xdc read -
0xde write Write All Mask Register Bits