MA31753
MA31753
DMA Controller (DMAC) For An MA31750 System
Replaces June 1999 version, DS3825-4.0
DS3825-5.0 January 2000
The MA31753 Direct Memory Access Controller (DMAC) is
a peripheral interface circuit design primarily for use with the
MA31750 microprocessor. Each DMAC provides up to four
independant, prioritised channels each of which can perform
DMA transfers between memory and/or I/O devices using the
MA31750 bus. Each channel has its own programmable
internal priority and can be masked under program control.
Further, individual channels have their own associated status
and control words enabling an individual channel to be re-
programmed without disturbing transfers which may be taking
place on other channels. Three basic transfer modes are
available:
Direct Memory to I/O peripheral transfers,
Direct I/O to Memory transfers,
Memory to Memory transfers,
I/O to I/O transfers.
The MA31753 interfaces directly to the MA31750 bus,
directly supporting on chip parity generation and supporting
expanded memory via an MA31751 MMU with either 1 MWord
(1750A mode) or 16MWords (1750B mode) of logical memory.
The MA31753 uses System memory to hold address and
count information for each transfer. Once this information has
been prepared by the processor the DMAC can conduct a
number of transfers without further processor intervention.
AS[0:3]
PS[0:3]
PB[0:3]
D[0:16]
A[0:15]
CSN
CLK
RESETN
DSN
AS
MION
OIN
RDWN
RDN
WRN
RDYN
GRANTN
REQN
LOCKN
DMAKN
DREQN[0:3]
DACKN[0:3]
DMAE
SEC/FIRSTN
DONEN
AKRDN
AKWRN
EXADEN
PEN
MPROEN
MA31753
DMAC
INTRN
REQINN
GEINN
GEOUTN
DPARN
DTON
VDD
VSS
FEATURES
s
Radiation Hard CMOS SOS Technology
s
Four Independant DMA Channels
s
MIL-STD-1750A or B Operation in an MA31750 System
s
Capable of Processor Independant Table Driven
Operation
s
Memory to Memory, I/O to Memory, Memory to I/O and
I/O to I/O Transfers Supported
s
Masking of Individual Channel DMA Requests
s
Simple MA31750 Bus Interface
s
Single Word, Double Word or Multi-Word Transfers for
each of the DMA Channels
s
Cascade Interface Allows for Channel Expansion
s
Programmable Channel Priority
s
Parity Checking Available
Figure 1: Pin Connections - Top View
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MA31753
1.0 GENERAL DESCRIPTION
The MA31753 DMA controller has 4 channels from which
independant transfers can be executed. These channels have
programmable priorities and can be masked. They can also be
enabled and disabled under software control.
The data can be transferred in several modes - single word
mode, double word mode and burst mode. It can be
transferred to and from both incrementing and decrementing
memory and IO addressing space. The single and double word
modes transfer data in 1 or 2 bus cycles when the simple
handshaking mechanism is enabled.
If more than 4 channels are required, several DMA
controllers can be cascaded together to give channel
expansion.
Once a channel has requested a transfer, and the bus
arbiter has granted bus control to the DMA, then the DMA
issues an acknowledge signal to the channel to be serviced. It
also pulses read or write strobes which can be gated with the
channel acknowledge signal to provide read and write strobes
for the requesting hardware.
DMA instructions can be programmed into memory on the
DMA. The transfers defined by these instructions can be
executed in sequence if they are “chained together”. In this
way, DMA transfers can take place continuously with data that
is held in seperate memory areas.
There is software access to all internal registers. These
registers have parity protection. By setting certain bits in
registers, requests can be initiated for area to area transfers on
channels 0 and 1. Interrupts for each channel can also be
issued.
2.0 INITIALISATION
After RESETN has been removed the DMA is
automatically initiated to be disabled with odd parity, the
channel priority order is 0, 1, 2, 3, C (C is the cascaded input)
and all channels are masked. At this point, before the DMA is
used further, the DMA instructions should be programmed into
the DMA internal RAM. Once all the instructions needed are in
place, the common features (ie. features that apply to all
channels) on the DMA can be programmed.These features
should be initialised to the users requirements.
The bus parity may be changed immediately after
RESETN goes inactive when the MA31750 reads the
configuration word ie. When the DMA detects the XIO address
0x8410, it snoops the data bus and latches the parity bit into an
internal copy. This internal copy can later be changed by
writing to the DMA Mode / Status register.
The DMA enable / disable follows the DMAE input - when
this input is high, the DMA device is enabled. When DMAE is
low, the DMA is disabled.
The channel priority and masking can be changed by
writing to the DMA Mode / Status register.
Once the common characteristics of the DMA have been
set up, the DMA individual channels can be programmed.
Each channel has a mode register that should be programmed
with an instruction number as that channel is activated (by
writing the mode word).
DMA
req
DMA
ack
DMA
req
DMA
ack
DMA
req
DMA
ack
DMA
req
DMA
ack
Channel 1
Handler
Channel 2
Handler
Channel 3
Handler
Channel 4
Handler
enable in
PRIORITIZER
DMARQN
A[0:15]
Double
RDWN
Cascaded
request
out (REQN)
Bus grantn
(GRANTN)
RDYN
BUS MANAGER
Grant enable
out (GEOUTN
Cascaded grant
(GEINN)
BUS INTERFACE
Figure 2: Block Diagram Representing the DMA Controller
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MA31753
3.0 DMA FUNCTIONALITY
Figure 2 shows a block diagram representing the structure
of the DMA controller. This figure also shows how the DMA
interfaces with the rest of the system.
Each DMA channel has 6 possible modes that it can
operate in. These are as follows:
3.1 IDLE MODE
The channel goes into IDLE mode after an active hardware
reset or after resetting the status flags. When in IDLE mode,
the channel goes into PEND_CHAIN mode when activated by
writing the Mode register. No parity check is done on this
register write.
3.2 PEND_CHAIN MODE
Once the channel has been activated, it goes from IDLE to
PEND_CHAIN mode. In this mode, the first instruction is read
(all 8 words). If a parity error is detected, the channel goes to
the ERROR mode. If the read is successful, the channel will
stay in the PEND_CHAIN mode until either an active request is
received or the Channel Request Pending bit is set in the
Channel Status Register. At this time, the channel progresses
to the PEND_REQ mode.
3.3 PEND_REQ MODE
In this mode, the Mode / Link word is checked to make sure
it doesn’t de-activate the channel (sending the device back to
IDLE mode). If the channel remains active, the device sits in
PEND_REQ mode until the system bus arbiter grants the DMA
bus control. Once this occurs, the transfer commences and the
DMA enters TRANSFER mode.
3.4 TRANSFER MODE
If at any time during the transfer an error occurs, the
channel is set into ERROR mode. If the transfers are clean of
errors, then the behaviour of the device is dependant on the
type of transfer mode that was programmed by the currently
executing instruction.
3.4.1 Single/Double Word and External Area to Area Mode
Within these modes, the DMA executes each data transfer
seperately, ie. between each single / double word transfer, the
request is removed. The DMA goes back into PEND_REQ
mode after each transfer and waits for the next request to be
granted.
3.4.2 Burst Area to Area Mode
With this type of transfer, the DMA transfers data whilst the
bus control is granted. The channel request signal remains
active. When control is removed by the arbiter, the device sits
in the PEND_TRANS mode until re-granted. If the burst mode
is area to area with interval timing, then between each transfer,
the channel has to count the interval.
Once a transfer has completed, the channel either sets the
EOT bit and sits waiting for this to be reset before it goes back
into INIT mode, or the instruction is chained and the channel
jumps back to the PEND_CHAIN mode where it can read the
next instruction details for the next transfer. If during any
transfer mode, the channel is de-activated, the channel goes
back to INIT mode. If at any time, an error is detected, the
device goes into ERROR mode.
3.5 ERROR MODE
This mode is entered from the PEND_CHAIN mode if a
parity error is detected during the instruction register reads.
The error mode can also be entered from theTRANSFER
mode. This can happen if PEN, MPROEN or EXADEN are
activated by trying to access one of the data transfer addreses.
An interrupt is generated in this mode. The only way to leave
this mode is to reset all the error flags.
3.6 WORD TRANSFER MODES
It is possible to run each channel in single, double, and
burst mode transfers.
3.6.1 Single Word Transfer
In single word transfer mode, the generation of each
request on a channel causes the DMA controller to issue an
external request that lasts for one bus cycle. The request is de-
activated before the end of the bus cycle to allow other users to
aquire bus control. If the transfer is to or from a device needing
longer than one machine cycle (2 CLK cycles) then the cycle
can be extended using handshaking of the DMA request and
acknowledge lines.
3.6.2 Double Word Transfer
In double word mode, each request on a channel causes
the DMA controller to request bus control for 2 machine cycles
to allow the transfer of 2 16-bit data words. The data is
transferred to consecutive addresses and the bus is locked
between each word transfer to protect the transfer. The most
significant word to be transferred has the lowest address and
is transferred first (following the 1750 standard). The request is
de-activated before the end of the second bus cycle to allow
other bus users to take control. If an extended cycle is needed,
the handshaking mechanism doesn’t word in this mode and
the RDYN signal must be kept high for as long as required.
3.6.3 Burst Mode
In burst mode, one request to the channel causes the DMA
to request bus control for a complete block of data to be
transferred. The DMA de-asserts the request line on the last
transfer cycle to allow other users to take bus control.
Consequently, if the transfers are chained together, the CPU
may be able to get bus control between 2 blocks of data
transfer. If extended bus cycles are needed, the RDYN
mechanism can be used (handshaking does not work in this
mode).
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MA31753
3.6.4 Area to Area Mode
In area to area mode, the transfers can be initiated either
by external requests or internally generated by the DMA
depending on the value in the interval timer (the software
generated requests controlleed by the interval timer can only
be used on channels 0 and 1). Each request makes the DMA
request bus control for 2 machine cycles. The transfers can
take place to and from IO and / or memory depending on how
the instruction programs the channel. The DMA de-asserts the
request during the second cycle unless the instruction has
programmed the channel to do “Continuous Internal Request”.
In this case, the request is only de-asserted on the last cycle of
the block. If extended bus cycles are needed, the RDYN
mechanism must be used as the handshaking does not work in
this mode.
3.6.5 Instruction Chaining
When the first request is received on a channel, it
accesses the DMA instruction number that is programmed in
the mode word. This instruction is read from internal DMA
RAM. This takes 16 CLK cycles (as there are 8 16-bit word in
the instruction). Bus control is not needed during these internal
RAM accesses. At the end of the 16 CLK cycles, the channel
has all the transfer information it needs and can begin to
transfer whenever it is granted bus control. Once the transfer
has completed, the channel checks that it is in chaining mode
and that the instruction is a chained instruction. If so, then as
the first instruction completes, the DMA can access the next
instruction (again taking 16 CLK cycles) and the transfers can
continue as bus control is granted.
3.6.6 Handshaking Mechanism
There is a handshaking mechanism available when using
single-word transfer mode. It works as follows:
For a memory read cycle:
1: The IO port issues a request.
2: The DMA requests and is granted bus control. The DMA
starts a memory read cycle. As well as the usual control
and strobes, the DMA also asserts the DACKN low for the
channel that it is responding to. The DACKN signal acts as
an IO port select.
3: Once valid data is available on the data bus ie. RDYN has
gone low, the DMA asserts AKWRN low. The IO port uses
AKWRN as a write strobe.
4: The IO port acknowledges the completed data read by de-
asserting DREQN.
5: When the DMA sees DREQN has gone high, it de-asserts
DACKN. At this time, the data is still valid and the IO port
may latch the data on AKWRN rising or any time in
between.
6: The DMA completes the cycle by de-asserting strobes etc.
7: The wait state generator finally de-asserts RDYN.
For a memory write cycle:
1: The IO port issues a request.
2: The DMA aquires bus control and starts a memory write
cycle, also asserting DACKN for the relevant channel.
3: The data bus is driven by the IO port. Valid data is
available when the IO port de-asserts DREQN. (DACKN is
still asserted so valid data must still be driven on the bus).
4: When the DMA senses DREQN high, it writes the valid
data from the IO port into memory.
5: The memory write is completed when RDYN goes low.
6: The DMA de-asserts DACKN and hence the IO port stops
driving the data bus.
If DREQN is de-asserted 2 or more CLK cycles before
AKRDN or AKWRN are asserted, then the handshaking
protocol does not apply and the cycle will simply use the RDYN
signal going low to terminate the cycle (both AKRDN and
AKWRN will rise as AS falls at the end of the cycle).
3.7 INTERRUPT GENERATION
The DMA shall generate an interrupt on the occurrance of
any of the following:
- A channel has reached an “End of Transfer” condition and
the EOT bit has been set in the channel status register.
- A channel has been stopped because
a) a bus timeout has occurred. (ie. either DREQN
(handshake mode) or RDYN is asserted for more than
256 CLK cycles)
b) an internal parity error was detected when reading a
DMA register with parity.
c) An odd block length was programmed in double word
mode.
The DMA will stop but will not generate an interrupt if
EXADEN, MPROEN or PEN are active at the end of an
external cycle.
If a parity error is detected whilst writing to the DMA
registers, the erroneous write will not let transfers commence.
The DMA generates interrupts by pulsing INTRN low. If more
than one error occurs simultaneously, INTRN is only pulsed
once. The interrupt can only be generated when the DMA is in
the ERROR mode. The only way to get out of this mode is to
reset all error flags.
3.8 CHANNEL MASKING AND STOPPING
Each channel can be masked individually by setting the
relevant bit in the DMA Mode / Status register. If the channel is
masked, only external requests are gated out - software
requests are still serviced.
Each channel can be stopped by de-activating the channel
by writing the Channel Mode register. This register can only be
written whilst in PEND_CHAIN mode or awaiting bus control.
Once the channel is de-activated, it returns to the IDLE mode.
3.9 PARITY CHECKING
Parity checks are done when DMA registers are being
written and when they are being accessed ie. when the
instructions are being read.
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MA31753
3.10 SOFTWARE PROGRAMMING
DMA requests can be generated in software by writing the
CRQP bit in the Channel Status register. If the channel is
active, the DMA will then request bus control. If the DREQN
signal on that channel is not active, the DMA finishes the cycle
as soon as the memory is ready. There is no handshaking with
the IO port. DACKN is deasserted when the memory is ready.
If DREQN is asserted but is masked, the handshaking is active
and operates normally.
Interrupts can be generated in software by setting either a
channel EOT flag or any error flag. This can only be done
when the DMA is in PEND_CHAIN mode. If an error flag is set,
the device goes straight to ERROR mode. If the EOT flag is
set, the device looks as if it has completed the transfer. It will
then just sit and wait for the EOT flag to be cleared before
entering IDLE mode. If both flags are set simultaneously, the
device remains in PEND_CHAIN mode. Setting an error flag
when EOT is set resets EOT and the device goes to ERROR
mode. Setting EOT when an error flag is set clears the error
and the DMA sits in the finish transfer mode.
3.11 CASCADING DMA CONTROLLERS
DMA controllers are cascaded in series. For each DMA
added, an extra 4 channels become available. To cascade the
devices, the strobes, control signals and address and data
busses are connected in parallel. Of the bus arbitration
signals, LOCKN and GRANTN should be connected in parallel
and REQINN, GEINN and GEOUTN shoudl be daisy-chained.
INTRN and PEN can either be ORed together with external
glue logic or input to seperate CPU interrupts. Figure 3 shows
the cascade connections.
GRANTN
REQN
Bus Interface Signals
REQINN
REQN
Bus
Arbiter
DMAC 1
GEOUTN
DMAC 2
GEINN
4
4
4
4
DREQN[0:3]
DREQN[0:3]
DACKN[0:3]
Figure 3: Cascading DMA Controllers
Bus Interface Signals
DACKN[0:3]
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