GR740-UM-DS, Nov 2017, Version 1.7
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GR740
The transfer descriptor words are structured as shown in tables 290-292 below.
Table 290.
GR1553B BC transfer descriptor word 0 (offset 0x00)
31
30
29
28
27
26
25
24
23
22
20
19
18
17
16
15
0
0
WTRIG EXCL
IRQE
IRQN
SUSE
SUSN
RETMD
NRET
STBUS
GAP
RESERVED
STIME
31
Must be 0 to identify as descriptor
30
Wait for external trigger (WTRIG)
29
Exclusive time slot (EXCL) - Do not schedule asynchronous messages
28
IRQ after transfer on Error (IRQE)
27
IRQ normally (IRQN) - Always interrupts after transfer
26
Suspend on Error (SUSE) - Suspends the schedule (or stops the async transfer list) on error
25
Suspend normally (SUSN) - Always suspends after transfer
24 : 23
Retry mode (RETMD). 00 - Retry on same bus only. 01 - Retry alternating on both buses
10: Retry first on same bus, then on alternating bus. 11 - Reserved, do not use
22 : 20
Number of retries (NRET) - Number of automatic retries per bus
The total number of tries (including the first attempt) is NRET+1 for RETMD=00, 2 x (NRET+1) for RETMD=01/
10
19
Store bus (STBUS) - If the transfer succeeds and this bit is set, store the bus on which the transfer succeeded (0
for bus A, 1 for bus B) into the per-RT bus swap register. If the transfer fails and this bit is set, store the opposite
bus instead. (only if the per-RT bus mask is supported in the core)
See section 16.4.3 for more information.
18
Extended intermessage gap (GAP) - If set, adds an additional amount of gap time, corresponding to the RTTO
field, after the transfer
17 : 16
Reserved - Set to 0 for forward compatibility
15 : 0
Slot time (STIME) - Allocated time in 4 microsecond units, remaining time after transfer will insert delay
Table 291.
GR1553B BC transfer descriptor word 1 (offset 0x04)
31
30
29
26
25
21
20
16
15
11
10
9
5
4
0
DUM
BUS
RTTO
RTAD2
RTSA2
RTAD1
TR
RTSA1
WCMC
31
Dummy transfer (DUM) - If set to ‘1’ no bus traffic is generated and transfer “succeeds” immediately
For dummy transfers, the EXCL,IRQN,SUSN,STBUS,GAP,STIME settings are still in effect, other bits and
the data buffer pointer are ignored.
30
Bus selection (BUS) - Bus to use for transfer, 0 - Bus A, 1 - Bus B
29:26
RT Timeout (RTTO) - Extra RT status word timeout above nominal in units of 4 us (0000 -14 us, 1111 -74
us). Note: This extra time is also used as extra intermessage gap time if the GAP bit is set.
25:21
Second RT Address for RT-to-RT transfer (RTAD2)
See table 293 for details on how to setup
RTAD1,RTSA1,RTAD2,RTSA2,WCMC,TR
for different transfer types.
Note that bits 15:0 correspond to the (first)
command word on the 1553 bus
20:16
Second RT Subaddress for RT-to-RT transfer (RTSA2)
15:11
RT Address (RTAD1)
10
Transmit/receive (TR)
9:5
RT Subaddress (RTSA1)
4:0
Word count/Mode code (WCMC)