Revision 1.02 – June 27, 2006
S5935 – PCI Product
Data Book
to generate a PCI interrupt. The pins are redefined as
follows:
PCI incoming and outgoing mailbox interrupts are
enabled in the Interrupt Control/Status Register
(INTCSR). The mailboxes can generate a PCI inter-
rupt (INTA#) under two conditions (individually
enabled). For an incoming mailbox full interrupt, INTA#
is asserted on the PCI clock rising edge after the Add-
On mailbox write completes. For an outgoing mailbox
empty interrupt, INTA# is asserted on the PCI clock
rising edge after the Add-On mailbox read completes
(the rising edge of RD#). INTA# is deasserted on the
next PCI clock rising edge after the PCI access to
clear the mailbox interrupt completes (TRDY#
deasserted).
Signal Pin
EA0/EMB0
Add-On Outgoing Mailbox
Mailbox 4, bit 24
Mailbox 4, bit 25
Mailbox 4, bit 26
Mailbox 4, bit 27
Mailbox 4, bit 28
Mailbox 4, bit 29
Mailbox 4, bit 30
Mailbox 4, bit 31
Mailbox 4, byte 3 load clock
EA1/EMB1
EA2/EMB2
EA3/EMB3
EA4/EMB4
EA5/EMB5
EA6/EMB6
EA7/EMB7
EA8/EMBCLK
Add-On Bus Interface
The Add-On mailbox interface behaves similar to the
PCI bus interface. Add-On writes to full outgoing mail-
boxes overwrite data currently in that mailbox. PCI
reads from empty incoming mailboxes return the data
that was previously contained in the mailbox.
If the S5935 is programmed to generate a PCI inter-
rupt (INTA#), on an Add-On write to outgoing mailbox
4, byte 3, a rising edge on EMBCLK generates a PCI
interrupt. The bits EMB7:0 can be read by the PCI bus
interface by reading the PCI incoming mailbox 4, byte
3. These bits are useful to indicate various conditions
which may have caused the interrupt.
Add-On incoming and outgoing mailbox interrupts are
enabled in the Add-On Interrupt Control/Status Regis-
ter (AINT). The mailboxes can generate the Add-On
IRQ# interrupt under two conditions (individually
enabled). For an incoming mailbox full interrupt, IRQ#
is asserted one PCI clock period after the PCI mailbox
write completes (TRDY# deasserted). For an outgoing
mailbox empty interrupt, IRQ# is asserted one PCI
clock period after the PCI mailbox read completes
(TRDY# deasserted). IRQ# is deasserted immediately
when the Add-On clears the mailbox interrupt.
When using the S5935 with a byte-wide boot device,
the capability to generate PCI interrupts with Add-On
hardware does not exist. In this configuration, PCI
incoming mailbox 4, byte 3 (Add-On incoming mailbox
4, byte 3) cannot be used to transfer data from the
Add-On - it always returns zeros when read from the
PCI bus. This mailbox byte is sacrificed to allow the
added functionality provided when a byte-wide boot
device is not used.
When the S5935 is used with a serial nv memory boot
device or no external boot device, the device pins
EA8:0 are redefined. EA7:0 become EMB7:0 data
inputs and EA8 becomes EMBCLK, a load clock. This
configuration allows the Add-On to generate PCI inter-
rupts with a low-to-high transition on EMBCLK. The
PCI incoming mailbox interrupt must be enabled and
set for mailbox 4, byte3 in the PCI Interrupt Control/
Status Register (INTCSR). EMBCLK should begin
high and be pulsed low, then high to be recognized.
The rising edge of EMBCLK generates the interrupt.
The rising edge of EMBCLK also latches in the values
on EMB7:0. The S5935 interrupt logic must be cleared
(INTA# deasserted) through INTCSR before further
EMBCLK interrupts are recognized.
BUS INTERFACE
The mailboxes appear on the Add-On and PCI bus
interfaces as eight operation registers. Four are outgo-
ing mailboxes, four are incoming mailboxes. The
mailboxes may be used to generate interrupts to each
of the interfaces. The following sections describe the
Add-On and PCI bus interfaces for the mailbox
registers.
PCI Bus Interface
The mailboxes are only accessible with the S5935 as
a PCI target. The mailbox operation registers do not
support burst accesses by an initiator. A PCI initiator
attempting to burst to the mailbox registers causes the
S5935 to respond with a target disconnect with data.
PCI writes to full outgoing mailboxes overwrite data
currently in that the mailbox. PCI reads from empty
incoming mailboxes return the data that was previ-
ously contained in the mailbox. Neither of these
situations cause a target retry or abort.
8-Bit and 16-Bit Add-On Interfaces
Some Add-On designs may implement an 8-bit or 16-
bit bus interface. The mailboxes do not require a 32-bit
Add-On interface. For 8-bit interfaces, the 8-bit data
bus may be externally connected to all four bytes of
the 32-bit Add-On interface (DQ 31:24, 23:16, 15:8,
7:0 are all connected). The Add-On device reading or
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