参数资料
型号: S5933QE
厂商: APPLIEDMICRO INC
元件分类: 总线控制器
英文描述: PCI BUS CONTROLLER, PQFP160
封装: PLASTIC, QFP-160
文件页数: 19/176页
文件大小: 823K
代理商: S5933QE
3-128
FIFO OVERVIEW
S5933
There are two special cases for the Add-On to PCI
FIFO management scheme. The first case is when
the FIFO is programmed to request the PCI bus only
when four or more locations are full, but the transfer
count is less than 16 bytes. In this situation, the FIFO
ignores the management scheme and finishes trans-
ferring the data. The second case is when the S5933
is configured for Add-On initiated bus mastering with
transfer counts disabled. In this situation, the FIFO
management scheme must be set to request the PCI
bus when one or more locations are full. AMREN and
AMWEN may be used to implement a specific FIFO
management scheme.
FIFO Bus Master Cycle Priority
In many applications, the FIFO is used as a PCI ini-
tiator performing both PCI reads and writes. This re-
quires a priority scheme be implemented. What
happens if the FIFO condition for initiating a PCI read
and a PCI write are both met?
Bits D12 and D8 in the Bus Master Control/Status
Register (MCSR) control the read and write cycle pri-
ority, respectively. If these bits are both set or both
clear, priority alternates, beginning with a read cycle. If
the read priority is set and the write priority is clear,
read cycles take priority. If the write priority is set and
the read priority is clear, write cycles take priority. Pri-
ority arbitration is only done when neither FIFO has
control of the PCI bus (the PCI to Add-On FIFO would
never interrupt an Add-On to PCI FIFO transfer).
FIFO Generated Bus Master Interrupts
Interrupts may be generated under certain conditions
from the FIFO. If PCI initiated bus mastering is used,
INTA# is generated to the PCI interface. If Add-On
initiated bus mastering is used, IRQ# is generated to
the Add-On interface. Interrupts may be disabled.
FIFO Interrupts may be generated from one or more of
the following during bus mastering: read transfer count
reaches zero, write transfer count reaches zero, or an
error occurs during bus mastering. Error conditions in-
clude a target or master abort on the PCI bus. Inter-
rupts on PCI error conditions are only enabled if one
or both of the transfer count interrupts are enabled.
The Add-On Interrupt Control/Status Register (AINT)
or the Interrupt Control Status Register (INTCSR) in-
dicates the interrupt source. The interrupt service
routine may read these registers to determine what
action is required. As mailboxes are also capable of
generating interrupts, this must also be considered in
the service routine. Interrupts are also cleared
through these registers.
BUS INTERFACE
The S5933 FIFO may be accessed from the Add-On
interface or the PCI interface. Add-On FIFO control
and status signals allow a simple interface to the
FIFO with either an Add-On CPU or programmable
logic. The following section describes the PCI and
Add-On interface behavior and hardware interface.
FIFO PCI Interface (Target Mode)
The S5933 FIFO may act as a standard PCI target.
FIFO empty/full status may be determined by the PCI
initiator by reading the status bits in the PCI Bus
Master Control/Status Register (MCSR).
The FIFO occupies a single 32-bit register location
within the PCI Operation Registers. A PCI initiator
may not perform burst accesses on the FIFO.
Each data phase of a burst causes the PCI initiator to
increment its address counter (even though only the
first address is driven at the beginning of the burst).
The initiator keeps track of the current address in
case a disconnect occurs. This allows the initiator to
continue the burst from where the disconnect oc-
curred. If the S5933 FIFO initiated a disconnect dur-
ing a PCI burst to the FIFO register, the burst would
be resumed at an address other than the FIFO loca-
tion (because the initiator address counter has
incremented). The S5933 always signals a discon-
nect if a burst to any PCI Operation Register is at-
tempted.
Because the PCI to Add-On FIFO and the Add-On to
PCI FIFO occupy a single location within the PCI and
Add-On Operation Registers, which FIFO is ac-
cessed is determined by whether the access is a
read or write. This means that once data is written
into the FIFO, the value written cannot be read back.
For PCI reads from the Add-On to PCI FIFO, the
S5933 asserts TRDY# and completes the PCI cycle
(Figure 3). If the PCI bus attempts to read an empty
FIFO, the S5933 immediately issues a disconnect
with retry (Figure 4). The Add-On to PCI FIFO status
indicators change one PCI clock after a PCI read.
For PCI writes to the PCI to Add-On, the S5933 as-
serts TRDY# and completes the PCI cycle (Figure 5).
If the PCI bus attempts to write a full FIFO, the
S5933 immediately issues a disconnect with retry
(Figure 6). The PCI to Add-On FIFO status indicators
change one PCI clock after a PCI write.
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