Table of Contents
Advertisement
3.3
Link speeds
The SpaceWire links can support a range of communication speeds, which are programmed by writing to registers. At reset
all links are configured to run at the base speed of 10 Mbits/sec. Only the transmission speed of a link is programmed as
reception is asynchronous. This means that links running at different speeds can be connected, provided that each device is
capable of receiving at the speed of the connected transmitter. The transmission speeds of all of the links on a given device
are related to the maximum transmission rate programmed for the complete device. This maximum transmission rate is
programmed through the transmit bitrate base register TRS_CTRL described in section 4.2.1.2. This max. transmission
bitrate is divided down to obtain the transmission frequency for each link. The division factor can be programmed separately
for each link via the Channel Link SpaceWire Mode Register CH_x_DSM_MODR register described in section 4.2.2.1.
This arrangement allows each link to be run at different transmission speeds, as shown in the table below (shown for
minimum and maximum link speeds):
Max. Transmit Speed
80
(TRS_CTRL = 0x08)
200
(TRS_CTRL = 0x14)
3.4
Errors on links
Link inputs can detect parity and disconnection conditions as errors. A single bit odd parity system will detect single bit
errors at the character level. The protocol to transmit NULL's in the absence of other characters enables disconnection of a
link to be detected. A disconnection error indicates that:
•
the link has been physically disconnected;
•
an error has occurred on the link or at the other end of the link, which may have then stopped transmitting.
The status bits in the CH_x_DSM_STAR registers flags that a parity, credit, sequence (ESC) and/or disconnect error has
occurred on the link. The errors can be detected independently. When a SpaceWire channel detects a parity, credit or
sequence error it halts its output. This is detected as a disconnect error at the other end of the link, causing this to halt its
output also. Detection of an error causes the link to be stopped. Thus, the disconnect behavior ensures that both ends are
stopped. Each end can then be restarted.
SMCS332SpW
User Manual
Link Speed Divider
– All Rights Reserved – Copyright per DIN 34 –
Link Speed [Mbit/s]
1
80
2
40
4
20
8
10
16
5
32
2,5
64
1,25 (min. Link speed)
1
200 (max. Link speed)
2
100
4
50
8
25
16
12,5
32
6,25
64
3,125
EADS Astrium GmbH, ASE2
Doc No: SMCS_ASTD_UM_100
Issue:
1.4
Updated: 9-Sep-2006
Page:
16 of 131
Advertisement
Table of Contents
