Hello Wolfgang,
Thank you again for your comments.
On 2013-01-08 18:39, Wolfgang Denk wrote:
Dear Christian Riesch,
In message <6cc4810c-1e2e-4ebf-912a-96936f035...@mary.at.omicron.at> you wrote:
Signed-off-by: Christian Riesch <christian.rie...@omicron.at>
---
board/omicron/calimain/calimain.c | 31 ++++++++++++++++++++++++++++++-
include/configs/calimain.h | 2 ++
2 files changed, 32 insertions(+), 1 deletion(-)
diff --git a/board/omicron/calimain/calimain.c
b/board/omicron/calimain/calimain.c
index 1060a1f..80e3893 100644
--- a/board/omicron/calimain/calimain.c
+++ b/board/omicron/calimain/calimain.c
@@ -1,5 +1,5 @@
/*
- * Copyright (C) 2011 OMICRON electronics GmbH
+ * Copyright (C) 2011-2013 OMICRON electronics GmbH
*
* Based on da850evm.c. Original Copyrights follow:
*
@@ -136,6 +136,35 @@ int board_init(void)
return 0;
}
+/* seed random number generator with uninitialized SRAM content */
+static void srand_sram(void)
+{
+ int *p;
+ int seed = 0;
+
+ for (p = (int *) 0x80000000; p < (int *) 0x8001ffff; p++)
+ seed ^= *p;
+
+ srand(seed);
+}
Note that your "uninitialized" SRAM content is probably not so much
random at all -
There are several papers around describing the use of initial SRAM value
after power up for the generation of random numbers. This is why I gave
it a try, and it works pretty well for me. I get a different seed for
each power-up cycle. I guess that the randomness is limited and that
part of the generated seed is more a fingerprint for the chip, therefore
it may not be good enough for security related stuff, but for my purpose
it's ok.
I guess, it is much less random than the originally
used timer value.
In my case the timer value is not random at all since it is reset to
zero at power-up. Since seeding the random number generator is always
done at the same time after power-up in the current code, the seed will
always be the same for my devices. Therefore the generated MAC address
will always be the same for all devices.
What exactly is your justification for such a change? Please
elucidate...
Actually I do not change anything ;-)
For the lsxl board that is currently the only user of eth_random_enet(),
nothing changes. get_timer(0) remains the source of the randomness for
this board. My patches only allow other boards to use a sources of
randomness that is available to them instead of forcing everyone to use
get_timer(0).
+int board_late_init(void)
+{
+ uchar enetaddr[6];
+
+ if (!eth_getenv_enetaddr("ethaddr", enetaddr)) {
+ srand_sram();
+ eth_random_enetaddr(enetaddr);
+ if (eth_setenv_enetaddr("ethaddr", enetaddr)) {
+ printf("Failed to set random ethernet address\n");
+ } else {
+ printf("Setting random ethernet address %pM.\n",
+ enetaddr);
+ }
+ }
+ return 0;
+}
NAK! You are but duplicating the code already present in net/eth.c
Apparently I am missing something here. I do not see a call of
eth_random_enetaddr() in net/eth.c. To which part of net/eth.c are you
referring?
Regards, Christian
This makes no sense.
Best regards,
Wolfgang Denk
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