#2743 HIGH Product: In manufacturing, multicast download of images is highly desirable.

[Zarro Boogs per Child]

#2743: In manufacturing, multicast download of images is highly desirable.
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  Reporter:  jg                   |       Owner:  dwmw2           
      Type:  defect               |      Status:  new             
  Priority:  high                 |   Milestone:  Production Start
 Component:  ofw - open firmware  |     Version:                  
Resolution:                       |    Keywords:                  
  Verified:  0                    |  
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Comment (by dwmw2):

 {{{
 shinybook /shiny/git/mtd-utils # ./serve_image ff0f::114 12345
 /export/olpc/dd.img 131072 950
 Inter-packet delay (avg): 1472µs
 Transmit rate: 950 KiB/s
 Checking CRC....24ead053
 Sending parity block: 10400000     (905 KiB/s)
 269278 KiB sent in 297483ms (905 KiB/s)
 }}}

 The tool sends 1400-byte UDP packets, with an extra parity packet per
 eraseblock for redundancy. It transmits the image once, although in
 production we'll want to just keep looping.

 2077/2081 packets were received by the XO sitting next to my laptop in the
 first pass; all 4 missed eraseblocks were received correctly in the second
 pass. Earlier testing showed that packets missed by one XO were likely to
 be missed by more than one -- so there's perhaps some mileage in having
 some kind of 'NAK' protocol when a block is missed, so that it can be
 resent immediately rather than waiting until next time around.

 Stats show that 2000 eraseblocks were received with all 95 packets, 80
 eraseblocks with 94 (which is also sufficient), and 1 each with 92, 79, 57
 and 55 packets. So the parity seems to be perfectly sufficient -- although
 that's in a relatively clean electrical environment and at a range of
 inches. More testing required.

-- 
Ticket URL: <http://dev.laptop.org/ticket/2743#comment:2>
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