ADSP-2192 AD [Analog Devices], ADSP-2192 Datasheet - Page 21

• Manufacturer Part Number: ADSP-2192
• Description: DSP Microcomputer
• Manufacturer: AD [Analog Devices]

The DSP memory interface on the ADSP-2192M only allows
reads/writes of 16-bit words. It cannot handle byte transactions.
Therefore, a 64-byte maxpacketsize means 32 DSP words. A
single byte cannot be transferred to/from the DSP. Endpoint 0
does not have this limitation. Because these FIFOs exist in DSP
memory, the DSP shares some pointer management tasks with
the USB core. For OUT transactions, the write pointer is con-
trolled by the USB core, while the read pointer is governed by
the DSP. The opposite is true for IN transactions.
Both the write and read pointers for each memory buffer would
begin at zero. All USB buffers operate in a circular fashion. Once
a pointer reaches the end of the buffer, it will need to be set back
to zero.
OUT Transactions (Host to Device)
When an OUT transaction arrives for a particular endpoint, the
USB core calculates the difference between the write and read
pointers to determine the amount of room available in the FIFOs.
If all of the OUT data arrives and the write pointer never catches
up to the read pointer, that data is Backed and the USB core
updates the Memory Buffer Write Offset register.
If at any time during the transaction the two pointers collide, the
USB block responds with a NAK indicating that the host must
resend the same data packet; in that case, the write pointer
remains unchanged.
If for some reason the host sends more data than the maxpack-
etsize, the USB core accepts it, as long as there is sufficient room
in the FIFO.
Because the DSP controls the read pointer, it must perform a
similar calculation to determine if there is sufficient data in the
FIFO to begin processing. Once The DSP has consumed some
amount of data, it will need to update the Memory Buffer Read
Offset register.
Table 23. Sub-ISA (PCI) Pin Descriptions
1
REV. 0
Pin Name
AD[15:0]
AD[18:16]
AD[31:22]
RST
CBE0
CBE1
CBE2
INTA
AD21
AD20
AD19
PME
CLK
CLKRUN
CLKRUN
o/d = Open Drain
PCI Direction
In/Out
In/Out
In/Out
In
In/Out
In/Out
In/Out
Out (o/d)
In/Out
In/Out
In/Out
Out (o/d)
In
In/Out
Out
1
ISA Alias
ISAD[15:0]
ISAA[3:1]
Unused
RST
IOW
IOR
AEN
IRQ
PDW1
PDW0
PME_EN
PMERQ
Unused
IOCHRDY
IOCHRDY
ISA Direction
In/Out
In
In
In
In
In
In
Out
In
In
In
Out (o/d)
In
Out
Out
–21–
IN Transactions (Device to Host)
When an IN transaction arrives for a particular endpoint, the
USB core once again computes how much read data is available
in the FIFO. It also determines if the amount of read data is
greater than or equal to the maxpacketsize. If both conditions are
met, the USB core will transfer the data. Upon receiving ACK
from the host, the USB core updates the Memory Buffer Read
Offset register.
If the amount of read data is less than the maxpacketsize (a short
packet), the USB core determines whether to send the data based
upon a NAK count limit. This is a 4-bit field in the Endpoint
Stall Policy register that can be programmed with a value indi-
cating how many NAKs should be sent prior to transmitting a
short packet. This allows flexibility in determining how IRPs are
retired via short packets.
Because the DSP controls the write pointer, it must determine if
there is sufficient room in the FIFO for placing new data. Once
it has completed writes to the FIFO, it needs to update the
Memory Buffer Write Offset register.
Sub-ISA Interface
In systems that combine the ADSP-2192M chip with other
devices on a single PCI interface, the ADSP-2192M Sub-ISA
mode is used to provide a simpler interface (to a PCI function
ASIC), which bypasses the ADSP-2192M’s PCI interface.
In this mode, the Combo Master assumes all responsibility for
interfacing the function to the PCI bus, including provision of
Configuration Space registers for the ADSP-2192M system as a
separate PnP function. In Sub-ISA Mode the PCI Pins are recon-
figured for ISA operation as shown in
ISA Description
Data
Register Address
Tie to GND in Sub-ISA Mode
Reset
Write Strobe
Read Strobe
Chip Select (Access Enable)
(CMOS) Interrupt (Active High)
PCI D-state MSB (inverted) Power-Down
PCI D-state LSB (inverted) Power-Down
PME Enable
Power Management Event
Tie to GND in Sub-ISA Mode
I/O Ready
Acknowledge
ADSP-2192M
Table
23.