Andy,
See comments below.
On 04/02/2015 02:11 AM, Andy Shevchenko wrote:
This series makes better approximation when baud rate divisor parameters are
calculated.
The algorithm is represent as Python script here [1]. First parameter is
algorithm (0 - original, 1 - after patch 1/2, 2 - after patch 2/2, 3 - memory
vs. performance: use precalculated scales).
I played with let's say standard baud rates (which I used for Quark) and
separately run algorithms 0 and 1 for range 100-5000 baud. Input frequency is
64MHz. It seems my algo shows better results in all cases. Here is a diff for
'standard' baud rates
(speed_hz, DBR, i, BR, j, PBR, real baud rate, difference):
--- result0 2015-04-02 00:38:48.845761004 +0300
+++ result1 2015-04-02 00:38:48.913760154 +0300
@@ -5,7 +5,7 @@
25000000 0 0 2 0 2 16000000 9000000
20000000 0 0 2 0 2 16000000 4000000
16667000 0 0 2 0 2 16000000 667000
-13333000 0 0 2 0 2 16000000 2667000
+13333000 0 0 2 1 3 10666666 2666334
This one is definitely a bug in the original due to dropping the
remainder in the 4.8 scale factor needed.
12500000 0 0 2 1 3 10666666 1833334
10000000 0 0 2 1 3 10666666 666666
8000000 0 1 4 0 2 8000000 0
@@ -17,36 +17,36 @@
3140500 0 1 4 2 5 3200000 59500
3125000 0 1 4 2 5 3200000 75000
3109500 0 1 4 2 5 3200000 90500
-2500000 0 1 4 3 7 2285714 214286
+2500000 0 3 8 1 3 2666666 166666
The rest of these I'm not sure about. The property is called
"spi-max-frequency" and the description in the bindings document is:
- spi-max-frequency - (required) Maximum SPI clocking speed of device in Hz
In the rest of the examples you've gotten a closer baud rate by
exceeding the "Maximum" value. I don't think you want best
approximation, I think you want closest without going over..
2000000 0 4 16 0 2 2000000 0
1563000 0 3 8 2 5 1600000 37000
-1250000 0 3 8 3 7 1142857 107143
+1250000 0 4 16 1 3 1333333 83333
1006000 0 5 32 0 2 1000000 6000
1000000 0 5 32 0 2 1000000 0
994000 0 5 32 0 2 1000000 6000
800000 0 4 16 2 5 800000 0
-781250 0 5 32 1 3 666666 114584
-625000 0 4 16 3 7 571428 53572
+781250 0 4 16 2 5 800000 18750
+625000 0 5 32 1 3 666666 41666
500000 0 6 64 0 2 500000 0
400000 0 5 32 2 5 400000 0
-390625 0 6 64 1 3 333333 57292
+390625 0 5 32 2 5 400000 9375
250000 0 7 128 0 2 250000 0
200000 0 6 64 2 5 200000 0
205313 0 6 64 2 5 200000 5313
-195313 0 7 128 1 3 166666 28647
-185313 0 7 128 1 3 166666 18647
+195313 0 6 64 2 5 200000 4687
+185313 0 6 64 2 5 200000 14687
125000 0 8 256 0 2 125000 0
100700 0 7 128 2 5 100000 700
100000 0 7 128 2 5 100000 0
-99300 0 8 256 1 3 83333 15967
+99300 0 7 128 2 5 100000 700
50000 0 8 256 2 5 50000 0
25000 0 9 512 2 5 25000 0
-10066 0 10 1024 3 7 8928 1138
-10016 0 10 1024 3 7 8928 1088
-9966 0 10 1024 3 7 8928 1038
-5065 0 11 2048 3 7 4464 601
-5040 0 11 2048 3 7 4464 576
-5015 0 11 2048 3 7 4464 551
+10066 0 11 2048 1 3 10416 350
+10016 0 11 2048 1 3 10416 400
+9966 0 11 2048 1 3 10416 450
+5065 0 12 4096 1 3 5208 143
+5040 0 12 4096 1 3 5208 168
+5015 0 12 4096 1 3 5208 193
1007 0 15 32768 0 2 976 31
1002 0 15 32768 0 2 976 26
997 0 15 32768 0 2 976 21
Patch 2 is RFC, since I don't know if all DSPI modules has that bit (at least
what I found on public for MC55xx) and how duty cycle is significant.
Not compiled. Not tested.
[1] http://pastebin.com/uy0CKc6b
Andy Shevchenko (2):
spi: fsl-dspi: increase precision of baud rate approximation
spi: fsl-dspi: use double baud rate in approximation
drivers/spi/spi-fsl-dspi.c | 50 +++++++++++++++++++++-------------------------
1 file changed, 23 insertions(+), 27 deletions(-)
Thanks,
Aaron
--
To unsubscribe from this list: send the line "unsubscribe linux-spi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
