[Trac #397] SD high-speed not working yet

[Zarro Boogs per Child]

#397: SD high-speed not working yet
---------------------+------------------------------------------------------
 Reporter:  cjb      |        Owner:  dilinger
     Type:  defect   |       Status:  new     
 Priority:  blocker  |    Milestone:  BTest-3 
Component:  kernel   |   Resolution:          
 Keywords:  relnote  |  
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Comment (by wmb at firmworks.com):

 I tested high-speed SD read speed under OFW, using the 4 SD cards that
 Alan Cunningham of Marvell sent me.  The results are:


 {{{
  Card               Measured       Marketing fluff
  ----------------   -----------    ----------------------------
  Panasonic 512 MB   17.9 MB/sec    (Pro High Speed 20MB/s 133x)
  SanDisk     1 GB   20.8 MB/sec    (Extreme III 20 MB/s)
  pq1         2 GB   21.2 MB/sec    (HiSpeed 150)
  Transcend   4 GB   17.7 MB/sec    (UltraSpeed 150x)

 }}}


 In the measured speeds above, MB means 1,000,000 bytes, not 1024*1024.

 The test program was as follows:

    ok select /sd
    ok attach-card .
    ok high-speed     \ In a future version I'll probably make high-speed
 automatic
    ok 1 if t( 10 0 do load-base 0 80 true r/w-blocks drop  loop )t  then

 That does 16 (hex 10) iterations of a 128-block (hex 80) read and times
 the result.  (Enclosing it in "1 if  ...  then" forces the interpreter to
 precompile the loop, so the time that it takes the interpreter to process
 the command line does not add to the measured time.

 I also did a little hack to reduce the software overhead - I pre-
 translated the DMA addresses so OFW didn't have to spend time doing that
 during the transaction setup phase.  Without that hack, the speeds were
 about 3% lower than those cited above.

 Note that this is a raw read, without going through any filesystem
 processing.  Just blocks.

 Read lengths longer than 128 blocks at a time (e.g. 129 blocks) failed
 with a data timeout.  I don't know where the limitation is at present.  I
 only tried the longer reads with one card (the pq1).

-- 
Ticket URL: <http://dev.laptop.org/ticket/397#comment:8>
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