6 initialization, 7 auto-negotiation, 8 serial interface width configuration – Texas Instruments VLYNQ Port User Manual
Page 16: Width, Section 2.7
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2.6
Initialization
2.7
Auto-Negotiation
2.8
Serial Interface Width Configuration
Peripheral Architecture
Note:
Not servicing read operations results in deadlock. The only way to recover from a deadlock
situation is to perform a hard reset. Read operations are typically not serviced due to read
requests that are issued to a non-existent remote VLYNQ device or they are not serviced
due to trying to perform reads on the VLYNQ memory map prior to establishing the link.
Generally, you should not use read operations to transfer data packets since the serial nature of the
interface could potentially result in longer latencies. See
for more information.
Since VLYNQ devices can be controlled solely over the serial interface (that is, no local CPU exists), an
automatic reliable initialization sequence (without user configuration) establishes a connection between
two VLYNQ devices, just after a VLYNQ module is enabled and auto-negotiation occurs. Auto-negotiation
is defined in
. The same sequence is used to recover from error conditions.
Bit 0 in the VLYNQ status register (LINK bit) is set to 1 when a link is established.
A link pulse timer generates a periodic link code every 2048 serial clock cycles. The link is lost when time
expires and no link code has been detected during a period of 4096 serial clock cycles.
Auto-negotiation occurs after reset. It involves placing a negotiation protocol in the outbound data and
processing the inbound data to establish connection information. The width of the data pins on the serial
interface is automatically determined at reset as a part of the initialization sequence. For a connection
between two VLYNQ devices of version 2.0 and later (VLYNQ on DM644x device is version 2.6), the
negotiation protocol using the available serial pins is used to convey the maximum width capability of each
device. The TXD data pins are not required to have the same width as the RXD data pins.
The auto width negotiation does not occur until after completion of the VLYNQ 1.x legacy width
configuration, which involves a period of 2000 VLYNQ 1.x system clock cycles for connection to VLYNQ
1.x devices. After the VLYNQ 1.x has determined its width, it receives the VLYNQ2.x auto width
negotiation protocol. The VLYNQ 1.x device does not recognize this protocol and transmits error codes
over the serial interface. The received error codes allow the VLYNQ 2.x devices to determine how many
serial pins are valid on the connected VLYNQ 1.x device.
Once the width is established, VLYNQ further identifies the version (version 1.x or version 2.x ) of the
remote VLYNQ. This better determines the capabilities of the connected VLYNQ device. This is software
readable via the VLYNQ auto-negotiation register (AUTNGO), bit 16 (0 = Ver 1.x , 1 = Ver 2.x), after the
link has been established.
The VLYNQWD bit in the pin multiplexing register 0 (PINMUX0) controls the data width on the DM644x
device, thus allowing you to program the serial interface width (as shown in
).
Table 2. Serial Interface Width
VLYNQWD
VLYNQ Data Width
00
VLYNQ TXD[0] , VLYNQ RXD[0]
01
VLYNQ TXD[0:1] , VLYNQ RXD[0:1]
11
VLYNQ TXD[0:2] , VLYNQ RXD[0:2]
10
VLYNQ TXD[0:3] , VLYNQ RXD[0:3]
For detailed information on the processor pin multiplexing and configuration register, see the pin
multiplexing information in the device-specific data manual.
VLYNQ Port
16
SPRUE36A – September 2007