<div dir="ltr"><div>I agree with Claudio's assessment. I also would suspect if you look at the disassembly that the function is leaf-optimized (uses retl instead of ret), which having this extra save/restore might correct for, but if you remove that then touching registers that are not in the %o (output) or %g (global) register families could cause some bad problems.<br>
<br>I would actually change the %17 to a register that is safe to use. This fix should also permit gcc to leaf-optimize the function still, since it can use an output register safely in that context.<br></div><div>Something like:<br>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
__asm__ __volatile__ ("
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
set " XSTR(NB_ITER_60US) ", %%o0; \</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
StartLoop1us:
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
dec 1, %%o0;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
cmp %%o0, 0;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
bne StartLoop1us;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
nop;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<span style="font-size:9pt;font-family:'Courier New'">
" : : "o0" );</span><br></div><br>or<br><br><div><span style="font-size:9pt;font-family:'Courier New'">
int count = </span><span style="font-size:9pt;font-family:'Courier New'">XSTR(NB_ITER_60US);</span></div><p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
__asm__ volatile ("
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
StartLoop1us:
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
dec 1, %0;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
cmp %0, 0;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
bne StartLoop1us;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
nop;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:medium none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<span style="font-size:9pt;font-family:'Courier New'">
" : "=r" (count));</span><br><div><br></div><div>And check the output of compiling by disassembling or compile with -S to see what assembly gcc creates when making this function.<br></div></div><div class="gmail_extra">
<br><br><div class="gmail_quote">On Tue, Apr 23, 2013 at 5:27 AM, Cláudio Silva <span dir="ltr"><<a href="mailto:claudiodcsilva@gmail.com" target="_blank">claudiodcsilva@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">Hello Leonard, <div><br></div><div>I would add a volatile after the __asm__ otherwize gcc can optimize away some of your code.<br>The windows underflow and overflow traps will occur during normal execution. It is expected behavior when you do a restore and the previous register window is invalid (marked as 1 in the $wim register). <br>
Regarding your code, without the save and restore instruction you are changing the current window %l7 register and gcc might be not expecting it. To solve this you will need to <span style="font-family:arial,sans-serif;font-size:13px">clobber the register as Chris described in the previous email. </span><span style="font-family:arial,sans-serif;font-size:13px"> </span></div>
<div><font face="arial, sans-serif">The save and restore instruction are not a good addition to that code, because they may trigger an underflow/overflow trap therefore increasing the execution time of that function.</font></div>
<div><font face="arial, sans-serif"><br>The random behavior you are seeing might be due to stack corruption originating from the %sp register of the new window (after the save) being set to an old value (from an older register window). </font><span style="font-family:arial,sans-serif">"save" should be "save %sp, -96 (?), %sp". Nevertheless this is just my quick guess ;)</span></div>
<div><span style="font-family:arial,sans-serif;font-size:13px"><br></span></div><div><span style="font-family:arial,sans-serif;font-size:13px">Regards, </span></div><span class="HOEnZb"><font color="#888888"><div><span style="font-family:arial,sans-serif;font-size:13px">Cláudio</span></div>
</font></span></div><div class="gmail_extra"><br><br><div class="gmail_quote"><div><div class="h5">On Tue, Apr 23, 2013 at 10:02 AM, Leonard Bise <span dir="ltr"><<a href="mailto:leonard.bise@syderal.ch" target="_blank">leonard.bise@syderal.ch</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5"><div dir="ltr">Hello all,<div><br></div><div>I'm having a problem regarding the processor window registers that I cannot explain easily mostly because I'm not super familiar with this subject.</div>
<div><br></div><div>
First, I'm using a LEON2 Sparc v8 processor and RTEMS 4.8 version which is required by our project.</div><div><br></div><div>We have a function using inline assembly to perform a flat delay, here is the code it use.</div>
<div><br></div><div><div style="border:1pt solid windowtext;padding:1pt 4pt">
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">void SCET_wait_2us(void)
{</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'"> {</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
/*#[ operation SCET_wait_2us() */</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
/* Performs a 60us delay using an ASM loop, this piece of code has been</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
* measured on HW to validate the duration is correct */</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
__asm__("
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
</span><span style="font-size:9pt;font-family:'Courier New';color:red">save;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
set " XSTR(NB_ITER_60US) ", %l7; \</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
StartLoop1us:
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
dec 1, %l7;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
cmp %l7, 0;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
bne StartLoop1us;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
nop;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
</span><span style="font-size:9pt;font-family:'Courier New';color:red">restore;
\</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
");</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">
/*#]*/</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'"> }</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
<p style="border:none;padding:0cm"><span style="font-size:9pt;font-family:'Courier New'">}</span><span style="font-size:9pt;font-family:'Courier New'"></span></p>
</div><div><br></div><div>Originally this code didn't have the save and restore instruction but our sub contractor added them because they had problems compiling. I find it an odd solution but whatever.</div><div>
<br></div><div>Once this code was implemented we started seeing random processor reset occurring in various contexts.</div><div><br></div><div>I tested this code while being in the Eclipse debugger and once the crash happened I noticed I had a segmentation fault in Eclipse. I used GRMON to check the processor register and noticed that the last trap that occurred was a window underflow trap 0x06.</div>
<div><br></div><div>I found in the RTEMS sources the code for this handler, and while I haven't understood everything I took out that the code was trying to recover from this error, is this correct?</div><div>
I copied the trap handler code below.</div><div><br></div><div>RTEMS 4.8 branch</div>file : rtems / c / src / lib / libcpu / sparc / reg_win / window.S<div><strong style="line-height:25px;font-size:18px;font-family:Helvetica,arial,freesans,clean,sans-serif;margin:0px;border:0px;padding:0px"><br>
</strong></div>SYM(window_underflow_trap_handler):<br><br> /*<br> * Calculate new WIM by "rotating" the valid bits in the WIM left<br> * by one position. The following shows how the bits move for a SPARC<br>
* cpu implementation where SPARC_NUMBER_OF_REGISTER_WINDOWS is 8.<br> *<br> * OLD WIM = 76543210<br> * NEW WIM = 07654321<br> *<br> * NOTE: New WIM must be stored in a global register since the<br>
* "save" instruction just prior to the load of the wim<br> * register will result in the local register set changing.<br> */<br><br> mov %wim, %l3 ! Calculate new WIM<br> sll %l3, 1, %l4 ! l4 = WIM << 1<br>
srl %l3, SPARC_NUMBER_OF_REGISTER_WINDOWS-1, %l5<br> ! l5 = WIM >> (Number Windows-1)<br> or %l5, %l4, %l5 ! l5 = (WIM << 1) |<br> ! (WIM >> (Number Windows-1))<br>
mov %l5, %wim ! load the new WIM<br> nop; nop; nop<br> restore ! Two restores to get into the<br> restore ! window to restore<br> ldd [%sp + 0x00], %l0 ! First the local register set<br>
ldd [%sp + 0x08], %l2<br> ldd [%sp + 0x10], %l4<br> ldd [%sp + 0x18], %l6<br> ldd [%sp + 0x20], %i0 ! Then the input registers<br> ldd [%sp + 0x28], %i2<br> ldd [%sp + 0x30], %i4<br>
ldd [%sp + 0x38], %i6<br> save ! Get back to the trap window.<br> save<br> jmp %l1 ! Re-execute restore.<br> rett %l2<div><br></div><div>From my understanding this code should not ever fail, is that correct?</div>
<div>What I'm not sure is that if this type of trap can be a common occurrence or if that means something went bad in the software.</div><div><br></div><div>Basically now I removed the save/restore and it seems to be working fine but I'll have to explain exactly what was happening before.</div>
<div>Is the compiler not expecting the user to add save/restore and could that lead to the behavior we see sometimes (processor reset). What are the usual way to handle this type of inline assembly? Never use save/restore?</div>
<div><br></div><div>Also our customer gave us a sequence of command to send to the software that would produce this reset systematically however when we got the equipment over here, I tried with the same code the sequence and it is not happening as often as they say. There seem to be a lot of randomness to this problem.</div>
<div><br></div><div>I really hope someone can provide some knowledge on this type of issue.</div><span><font color="#888888">-- <br><div><span><div><b><img><br></b></div><div>
<b>Léonard Bise</b></div><div>Software Design Engineer
</div><div>Direct Line <a href="tel:%2B41%20%280%2932%20338%209902" value="+41323389902" target="_blank">+41 (0)32 338 9902</a></div><div><br></div><div><b>SYDERAL SA</b></div><div>Neuenburgstrasse 7</div><div>CH-3238 Gals (Switzerland)</div>
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