Hello all,
I've been toying with this idea for a while and I found time and played around
a bit the last couple of days. The principle here is that with model huge, most
source files can be allocated to any code segment. The reasoning is that with a
'large' project, manual bank assignment requires a fair bit of maintenance and,
for the not-so-experienced user, can lead to bank overflows and 'why on earth
is my device crashing all the time?' moments.
What I've done with contiki for cc2430 is, I've written a script which gets
invoked by the build system. Things work like this:
- For sources that need to be in a certain segment, we specify so with a pragma
or with --codeseg (e.g. sources with ISRs).
- Compile everything and link. Free-to-reallocate modules are initially
assigned to a dummy segment
- The script reads the mem, map and rel files for information on code sizes
- We calculate the remaining free space of each bank by subtracting
pre-allocated code size from their capacity. Pre-allocated in this context also
means CONST, startup code, huge libraries etc
- We then allocate the remaining segments to banks automatically. This problem
is a very simple bin-packing variant, which can be solved with a very fast
heuristic (first-fit, decreasing is what I've done but there are probably
better approaches)
- Having reached a feasible target assignment, we edit each modules's .rel
in-place and then re-link.
So users are free to manually specify as many assignments as they like.
I built a 6lowpan border router for cc243x (Sensinode n601 NanoRouters) with
this technique. The output at the end of this message shows what I'm doing. As
can be seen, the resulting build is rather crowded but segments are getting
filled up quite nicely. The image has so far been working as intended
Having to rely on Make, a script and two linker invocations, the current
approach is a bit ugly. I am now planning to try and dig through the SDCC
sources, see if I can make this built-in. My initial thoughts about this:
- It would need a new linker argument in order to specify the capacity of each
bank. Something like -Wl-xyzBANK1=0x8000. Probably also a new linker argument
to turn the feature on/off
- A way of specifying that a source is free to move around. This could be as
simple as a reserved codeseg keyword, e.g. --codeseg __ANY or it could be a new
compiler argument. In the rel file, the A __ANY line would probably be enough
(?)
Any form of feedback would be great. Do you think this is
reasonable/feasible/remotely interesting? Any caveats I should watch out for?
Best Regards and as ever, thank you for your time and for all the efforts
maintaining SDCC
George
First Link
===============
sdcc --model-huge --stack-auto -DSDCC_CC2430 --out-fmt-ihx --xram-loc 0xE000
--xram-size 0x1F00 --code-loc 0x00000 --code-size 0x20000 -Wl-bBANK1=0x018000
-Wl-r -o border-router.ihx obj_sensinode/contiki-sensinode-main.rel
obj_sensinode/border-router.app.rel -llibsdcc.lib -lcontiki-sensinode.lib
...
Bank Allocation
===============
python ../../../cpu/cc2430/bank-alloc.py border-router
obj_sensinode/segment.rules
Total Size = 114797 bytes (100987 bankable, 2029 user-allocated, 11781
const+libs)
Preallocations: HOME=13810, BANK1=0, BANK2=0, BANK3=0
Bin-Packing results (target allocation):
Segment - max - alloc
HOME 32768 18564
BANK1 32768 32758
BANK2 32768 32762
BANK3 30720 30713
Final Link
===============
sdcc --model-huge --stack-auto -DSDCC_CC2430 --out-fmt-ihx --xram-loc 0xE000
--xram-size 0x1F00 --code-loc 0x00000 --code-size 0x20000 -Wl-bBANK1=0x018000
-Wl-r -Wl-bBANK2=0x028000 -Wl-bBANK3=0x038000 -o border-router.ihx
obj_sensinode/contiki-sensinode-main.rel obj_sensinode/border-router.app.rel
-llibsdcc.lib -lcontiki-sensinode.lib
...
Report
===============
Code footprint:
Area Addr Size Decimal
---------------------------------- -------- -------- --------
HOME,CSEG,CONST,XINIT,GS* 00000000 00004884 = 18564. bytes
(REL,CON,CODE)
BANK1 00018000 00007FF6 = 32758. bytes
(REL,CON,CODE)
BANK2 00028000 00007FFA = 32762. bytes
(REL,CON,CODE)
BANK3 00038000 000077F9 = 30713. bytes
(REL,CON,CODE)
Other memory:
Name Start End Size Max
---------------- -------- -------- -------- --------
PAGED EXT. RAM 0 256
EXTERNAL RAM 0xe000 0xf664 5733 7936
ROM/EPROM/FLASH 0x0000 0x3f7f8 114797 131072
------------------------------------------------------------------------------
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