3. Serial RapidIO Electrical Interface > Clocking
70
Tsi578 User Manual
June 6, 2016
Integrated Device Technology
www.idt.com
System software can force a downgrade in port mode by writing the OVER_PWIDTH field on either
the Tsi578 or in its link partner (see
“RapidIO Serial Port x Control CSR” on page 281
operating link width is available in the INIT_PWIDTH field. Software may need to manage ackID
recovery for the link partner when changing port usage between lanes A and C.
3.3.2.1
Degraded Link Mode
When a 4x port has degraded to a 1x mode, software may attempt to recover to 4x mode by using the
FORCE_REINIT bit in the
“RapidIO Port x Control Independent Register” on page 319
.
3.4
Clocking
Serial RapidIO ports use source clocked transmission; the clock is embedded in the data stream using
8B/10B encoding. The Tsi578 recovers the embedded clock in the received data stream and generates a
separate clock (based on S_CLK) to transmit its own data.
The Tsi578 uses only one external differential clock source (S_CLK_P/N) as the reference to generate
all internal clocks for processing the data. When the frequency of the reference clock is set at
156.25 MHz, Tsi578 can support three different RapidIO standard signaling rates (3.125 Gbps,
2.5 Gbps, and 1.25 Gbps).
shows the port speeds and bandwidths supported by the Tsi578. For
more information on clocking refer to
“Clocks, Resets and Power-up Options” on page 205
and
.
It is necessary to know if the link partner can continue to communicate when changing the
port width between Lanes A and C. Refer to the
“RapidIO Serial Port x Control CSR”
in the
link partner to determine the capability of the link partner.
Connecting four 1x links to a 4x port is not supported. Doing so results in the port failing to
achieve lane alignment.
Table 5: Reference Clock Frequency and Supported Serial RapidIO Data Rates
Reference
Clock
Frequency
(S_CLK_p/n)
Supported
Data Rate
SP_IO_SPEED[1:0]
Setting
Default Speed for
all Ports
User Bandwidth
(1x mode)
User Bandwidth
(4x mode)
156.25MHz
a
a.
For information about 125 MHz S_CLK refer to
.
1.25 Gbit/s
00
1.25 Gbit/s
1.0 Gbit/s
4.0 Gbit/s
2.50 Gbit/s
01
2.50 Gbit/s
2.0 Gbit/s
8.0 Gbit/s
3.125 Gbit/s
10
3.125 Gbit/s
2.5 Gbit/s
10 Gbit/s
N/A
11
(Illegal)
Undefined
Undefined
Undefined