GR740-UM-DS, Nov 2017, Version 1.7 410 www.cobham.com/gaisler
GR740
The receiver is activated as soon as the link interface leaves the error reset state. Then after a NULL is
received it can start receiving any characters. It detects parity, escape and credit errors which causes
the link interface to enter the error reset state. Disconnections are handled in the link interface part in
the tx clock domain because no receiver clock is available when disconnected.
Received Characters are flagged to the host domain and the data is presented in parallel form. The
interface to the host domain is shown in figure 49. L-Chars are the handled automatically by the host
domain link interface part while all N-Chars are stored in the receiver FIFO for further handling. If
two or more consecutive EOPs/EEPs are received all but the first one are discarded.
35.4 Time-Code distribution
Time-codes are control codes that consists of two control flags (bits 7:6) and a time value (bits 5:0),
and they are used to distribute time over the SpaceWire network. The current time value (value of lat-
est received or transmitted time-code), and control flags, can be read from the Time-code register
(TC).
35.4.1 Receiving time-codes
When a control code is received, and either the control flags (bits 7:6) have value “00”, or control flag
filtering is disabled (CTRL.TF bit set to 0), then the received control code is considered to be a Time-
Code. If Time-Code reception is enabled (CTRL.TR bit set to 1) then the received time value is stored
in the TC.TIMECNT field. If the received time value equals TC.TIMECNT+1 (modulo 64), then the
Time-Code is considered valid.
When a valid Time-Code is received, in addition to the time value being updated, the received control
flags are stored to the TC.TCTRL field. Also, when a valid Time-Code is received, the STS.TO bit is
set to 1, and an AMBA interrupt is generated if the CTRL.IE bit and CTRL.TQ bit are both set to 1.
35.4.2 Transmitting time-codes
Time-Codes can be transmitted through the AMBA APB registers. In order to send a Time-code,
Time-Code transmission must be enabled by setting the CTRL.TT bit to 1. To transmit a time-code
through the register interface the CTRL.TI bit should be written to 1. When the bit is written the cur-
rent time value (TC.TIMECNT field) is incremented, and a Time-Code consisting of the new time
value together with the current control flags (TC.TCTRL field) is sent. The CTRL.TI bit will stay
high until the Time-Code has been transmitted. If Time-Code transmission is disabled, writing the
CTRL.TI bit has no effect.
Note that the link interface must be in run-state in order to be able to send a Time-Code.
35.5 Receiver DMA channels
The receiver DMA engine handles reception of data from the SpaceWire network to different DMA
channels.
Receiver Clock Domain
Host Clock Domain
Receiver
D
DV
Got Time-code
Got FCT
Got NChar
Time-code[7:0]
NChar[7:0]
Figure 49. Schematic of the link interface receiver.
Got EEP
Got EOP
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