hello Friends,
I've been going over the AMBA AHB specifications and something is not clear to me
1). Shall all AHB slaves support WRAP4,8 or16 burst operation or not?
2). The Master access the slave by WRAPx operation, but the slave doesn't support this operation,
how does it reponse to the master?
Hope to see the replies soon.
Thanks!!!
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Shall slave support WRAPx burst operation or not?
all slaves support WRAPx burst operation or not?
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JD 
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Posted 11 October 2011 - 08:48 AM
1. Slaves do have to "support" any legal incoming transfers, but "support" could be as simple as returning an ERROR response.
2. As above, if the slave doesn't support the requested transfer type, it just needs to return an ERROR response, and the master's abort handler then has to work out how to get round the problem.
Looking at your specific questions involving WRAPx type bursts, does your slave use the HBURST information to improve performance, but cannot support the WRAP style of bursting, or are you just wanting to implement a simple slave type, and the WRAPx burst looks too complex ?
If you are not using the HBURST information, you could just look at HTRANS[1], and if it is high (i.e. a NONSEQ or SEQ access) then you just perform a single access (not caring about the burst type). Unlike AXI, in AHB the address is supplied for each transfer in a burst, so there is no need for any complex address incrementing/wrapping logic in the simple slave.
If you have a slave design that does support defined length INCRx bursts, but for some reason not WRAPx bursts, you can just return ERROR responses to each beat of the WRAPx burst, however this would limit the applications your slave could be used in.
JD
2. As above, if the slave doesn't support the requested transfer type, it just needs to return an ERROR response, and the master's abort handler then has to work out how to get round the problem.
Looking at your specific questions involving WRAPx type bursts, does your slave use the HBURST information to improve performance, but cannot support the WRAP style of bursting, or are you just wanting to implement a simple slave type, and the WRAPx burst looks too complex ?
If you are not using the HBURST information, you could just look at HTRANS[1], and if it is high (i.e. a NONSEQ or SEQ access) then you just perform a single access (not caring about the burst type). Unlike AXI, in AHB the address is supplied for each transfer in a burst, so there is no need for any complex address incrementing/wrapping logic in the simple slave.
If you have a slave design that does support defined length INCRx bursts, but for some reason not WRAPx bursts, you can just return ERROR responses to each beat of the WRAPx burst, however this would limit the applications your slave could be used in.
JD
This post has been edited by JD: 12 October 2011 - 08:09 AM
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