Pci target retry, Pci target disconnect, Pci target abort – Rainbow Electronics DS3131 User Manual
Page 125: 5 pci target retry, Figure 10-6. pci target retry, 6 pci target disconnect, Figure 10-7. pci target disconnect
DS3131
125 of 174
10.1.5 PCI Target Retry
Targets can terminate the requested bus transaction before any data is transferred because the target is
busy and temporarily unable to process the transaction. Such a termination is called a target retry and no
data is transferred. A target retry is signaled to the initiator by the assertion of PSTOP and not asserting
PTRDY on the initial data phase (
Figure 10-6
). When BoSS is a target, it only issues a target retry when
the host is accessing the local bus. This occurs when the local bus is operating in the arbitration mode. It
is busy at the instant the host requests access to the local bus. See Section
11.1
for more details about the
operation of the local bus.
Figure 10-6. PCI Target Retry
10.1.6 PCI Target Disconnect
A target can prematurely terminate a transaction by asserting PSTOP (
Figure 10-7
). Depending on the
current state of the ready signals when PSTOP is asserted, data may or may not be transferred. The
target always deasserts PSTOP when it detects that the initiator has deasserted PFRAME. When BoSS is
a target, it disconnects with data after the first data phase is complete, if the master attempts a burst
transaction. This is because the device does not support burst transactions when it is a target. When it is
an initiator and experiences a disconnect from the target, it attempts another bus transaction (if it still has
the bus granted) after waiting either one (disconnect without data) or two clock cycles (disconnect with
data).
Figure 10-7. PCI Target Disconnect
1
2
3
4
5
6
7
8
9
10
PCLK
PFRAME
PSTOP
PDEVSEL
1
2
3
4
5
6
7
8
9
10
PCLK
PFRAME
PSTOP
PDEVSEL
PTRDY
PIRDY