
GR716-DS-UM, May 2019, Version 1.29
183
www.cobham.com/gaisler
GR716
The branch condition word is formed as shown in table 177.
Table 175.
GR1553B transfer descriptor result word (offset 0x0C)
31
30
24
23
16
15
8
7
4
3
2
0
0
Reserved
RT2ST
RTST
RETCNT
RES
TFRST
31
Always written as 0
30:24
Reserved - Mask away on read for forward compatibility
23:16
RT 2 Status Bits (RT2ST) - Status bits from receiving RT in RT-to-RT transfer, otherwise 0
Same bit pattern as for RTST below
15:8
RT Status Bits (RTST) - Status bits from RT (transmitting RT in RT-to-RT transfer)
15 - Message error, 14 - Instrumentation bit or reserved bit set, 13 - Service request,
12 - Broadcast command received, 11 - Busy bit, 10 - Subsystem flag, 9 - Dynamic bus control acceptance, 8 - Termi-
nal flag
7:4
Retry count (RETCNT) - Number of retries performed
3
Reserved - Mask away on read for forward compatibility
2:0
Transfer status (TFRST) - Outcome of last try
000 - Success (or dummy bit was set)
001 - RT did not respond (transmitting RT in RT-to-RT transfer)
010 - Receiving RT of RT-to-RT transfer did not respond
011 - A responding RT:s status word had message error, busy, instrumentation or reserved bit set (*)
100 - Protocol error (improperly timed data words, decoder error, wrong number of data words)
101 - The transfer descriptor was invalid
110 - Data buffer DMA timeout or error response
111 - Transfer aborted due to loop back check failure
* Error code 011 is issued only when the number of data words match the success case, otherwise code 100 is used. Error code 011 can be
issued for a correctly executed “transmit last command” or “transmit last status word” mode code since these commands do not reset the status
word.
Table 176.
GR1553B BC Transfer configuration bits for different transfer types
Transfer type
RTAD1
(15:11)
RTSA1
(9:5)
RTAD2
(25:21)
RTSA2
(20:16)
WCMC
(4:0)
TR
(10)
Data buffer
direction
Data, BC-to-RT
RT address
(0-30)
RT subaddr
(1-30)
Don’t care
0
Word count
(0 for 32)
0
Read
(2-64 bytes)
Data, RT-to-BC
RT address
(0-30)
RT subaddr
(1-30)
Don’t care
0
Word count
(0 for 32)
1
Write
(2-64 bytes)
Data, RT-to-RT
Recv-RT
addr (0-30)
Recv-RT
subad. (1-30)
Xmit-RT
addr (0-30)
Xmit-RT
subad. (1-30)
Word count
(0 for 32)
0
Write
(2-64 bytes)
Mode, no data
RT address
(0-30)
0 or 31 (*)
Don’t care
Don’t care
Mode code
(0-8)
1
Unused
Mode, RT-to-BC RT address
(0-30)
0 or 31 (*)
Don’t care
Don’t care
Mode code
(16/18/19)
1
Write
(2 bytes)
Mode, BC-to-RT RT address
(0-30)
0 or 31 (*)
Don’t care
Don’t care
Mode code
(17/20/21)
0
Read
(2 bytes)
Broadcast
Data, BC-to-RTs
31
RTs subaddr
(1-30)
Don’t care
0
Word count
(0 for 32)
0
Read
(2-64 bytes)
Broadcast
Data, RT-to-RTs
31
Recv-RTs
subad. (1-30)
Xmit-RT
addr (0-30)
Xmit-RT
subad. (1-30)
Word count
(0 for 32)
0
Write
(2-64 bytes)
Broadcast
Mode, no data
31
0 or 31 (*)
Don’t care
Don’t care
Mode code
(1, 3-8)
1
Unused
Broadcast
Mode, BC-to-RT
31
0 or 31 (*)
Don’t care
Don’t care
Mode code
(17/20/21)
0
Read
(2 bytes)
(*) The standard allows using either of subaddress 0 or 31 for mode commands.