
TNETA1560
ATM SEGMENTATION AND REASSEMBLY DEVICE
WITH SBUS HOST INTERFACE
SDNS010C – JANUARY 1994 – REVISED OCTOBER 1995
39
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
PRINCIPLES OF OPERATION
FIFO-maximum-depth registers
Unused (bits 31 – 20) Max_RX_FIFO_Depth (bits 19 – 10)
Max_TX_FIFO_Depth (bits 9 – 0)
This is the only set of statistics collected by the SAR, which is useful information for queuing analysis in different
platforms with varying SBus-clock speeds and latencies. These registers are not of the read-and-reset variety
and must be explicitly set to zero to restart the measurement.
SBus physical-address mapping (in SBus-slave mode)
The SAR allows the host to access various peripheral devices and internal registers via an SBus-slave mode.
The device connects to the SBus physical-address bits (15–0) and (24–23). To access the PHY-layer register,
the software driver uses the SBus address offset given in Table 13. The SBus interface on the TNETA1560 uses
byte addressing to access the PHY-layer registers. During read operations, the data byte received from the
PHY-layer device is copied four times to make a 32-bit data word that is transferred across the bus. In a write
operation to a PHY-layer register, the software writes a valid data byte on SBD31–SBD24 because the SBus
uses the big-endian convention.
The accesses to the EPROM are similar to the read operations to the PHY-layer registers with the difference
being that the SBACK signals are set to 101 to indicate byte accesses.
peripheral devices
Table 13 specifies the SAR-slave mode SBus physical-address ranges for the SAR peripheral devices.
Table 13. SBus Physical Addresses for SAR Peripheral Devices
ADDRESS – 24 BITS
(hex)
000000-00FFFF
DESCRIPTION
ADDRESS
BITS
16
READ/WRITE
EPROM addresses
Read only
400000-40FFFF
PHY-layer register addresses
16
Read/write
C00000-C0FFFF
Control-memory addresses
14
Read/write
SBus SAR registers
The SBus SAR internal registers have an SBus physical-address base value of hex 800000. Table 14 specifies
the offset from this address for various SAR registers.
Table 14. SBus Physical Addresses for SAR Registers
OFFSET – 8 BIT
(hex)
00
DESCRIPTION
READ/WRITE
Software reset
Write only
04
Status register
Read only
08
Interrupt-mask register
Read/write
0C
Configuration register
Read/write
10
Reserved
14
BWG-table-size register
Read/write
18
TX/RX FIFO-maximum-depth register
Read/write
1C
Reserved
20
Clear-transmit-freeze command
Write only
24
Clear-receive-freeze command
Write only