[fpc-devel] Arm Thumb2 - Stellaris status

John Clymer john at johnclymer.net
Mon Aug 22 12:59:03 CEST 2011 

Ramtop for a generic part defined as having 1 MB of SRAM

In the generic startup file, place an 8 KB array, inside a chunk of assembly, 
set stack_top = top of the array.  So long as the program doesn't exceed the 
SRAM space AND the program doesn't exceed the array size - no problem.  (The 
actual size will have to be debated a bit, I think 8KB should suffice - but this 
would preclude small devices from being used this way.)





________________________________
From: Geoffrey Barton <mrb at periphon.net>
To: FPC developers' list <fpc-devel at lists.freepascal.org>
Sent: Sun, August 21, 2011 7:06:05 PM
Subject: Re: [fpc-devel] Arm Thumb2 - Stellaris status



On 21 Aug 2011, at 15:33, John Clymer wrote:

As part of my table-ization of cpuinfo.pas, I am including a generic part for 
each (no code published for this yet.)  The caveat to this is that FLASH size 
and SRAM sizes are just set to extremely large (1 MB each for now).  Which means 
if the code size exceeds the space of the device - the compiler/linker will not 
catch the overflow of the available resource.  (Running objsize on the ELF file 
will display the sizes - so I just run that after every successful compile.)
>
As I pointed out, this will always fail because the stacktop is set beyond the 
available ram. It will cause an exception I think. How do you propose to be able 
to set the actual ram top for the generic part, or am I missing something?



>Also, still testing, but I have the "interrupt" reserved word working (more or 
>less, more testing needed.)  This takes the interrupt codeword with an integer.  
>The integer is the offset into the vectors table.  If no interrupt is provided 
>for the given address, it defaults to DefaultHandler in the startup file - which 
>is just a continual loop - so one can breakpoint on it.  (This can be enabled / 
>disabled via a define in the source.)  This is should only be enabled for the 
>embedded target - but I need to double check to ensure that is the case.
>
This is a useful development; ideally the integer would be backed by an 
enumeration as it is a big table. One thing which I did find missing was the 
interrupt enable and disable assembler codes, so I patched them with data bytes 
hidden in functions. The keil C compiler does not like these if you link to 
units doing this (throws a data/code wobbly). See the file attached to bug 
tracker ID0017365 for how I hacked interrupts.


Fortunately, I have a few days off before the school semester starts - so I will 
be working on this quite heavily over the next few days.
>
all power to your elbow...

Geoffrey



>John
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________________________________
From: Geoffrey Barton <mrb at periphon.net>
>To: FPC developers' list <fpc-devel at lists.freepascal.org>
>Sent: Sun, August 21, 2011 6:01:22 PM
>Subject: Re: [fpc-devel] Arm Thumb2 - Stellaris status
>
>
>On 20 Aug 2011, at 15:46, David Welch wrote:
>
>>> 
>>> 
>>> The great strength of ARM is that the peripherals, even if in different 
>>>locations in different manufacturers parts, are identical in hardware terms if 
>>>they are all cortex m3; that is the IP which they license from ARM.com. So maybe 
>>>that is another reason for keeping the peripheral offset definitions and 
>>>peripheral drivers separate and out of the compiler.
>>> 
>>> Geoffrey
>>> 
>>> 
>> 
>> Not sure what you are saying here, almost none of the peripherals are the same 
>>from vendor to vendor.  With the cortex-m3 the systick timer and the VNIC for 
>>example are from ARM, sure, but the majority of the items you are going to use 
>>timers, dma, pwm, gpio, clocks and enables, etc are vendor specific and vastly 
>>different from vendor to vendor. Within a vendor they are very similar if not 
>>the same but from ti to st most of the items are not compatible, likewise from 
>>ti to lpc/nxp or ti to atmel, etc.
>
>You are right, of course. I have not looked at the data for other than Stellaris 
>devices, I just generalised from the ARM TRM.
>
>> 
>> Normally these are libraries and not buried in the compiler proper, I agree 
>>with that.  Perhaps that is what you were saying and I misunderstood.
>
>not quite, but it is my aspiration :-)
>
>> 
>> And as with libraries you can take them or leave them, that would want to be 
>>the case here (without having to dig into the compiler proper). Would need to 
>>roll your own target to avoid/modify a library.  Ideally with the compiler you 
>>want to specify the arm core to take advantages of instructions each newer core 
>>supports.  Not use them to tie to boards or systems.
>> 
>> I was hoping for thumb support but I now see that the choices are limited to 
>>arm and thumb+thumb2 (without any separation between thumb and thumb2).  
>>Actually thumb2 wasnt working for me, I got an arm+thumb2 mix, so I will ride 
>>this along for a while and see what comes up, otherwise limit my use to ARM 
>>targets, or start working on a thumb backend.  Adding backends as well as arm 
>>embedded are of interest to me so I may work on a little of both.
>> 
>> So far it seems to be very straight forward to add a platform/device to fpc arm 
>>embedded, so if the stock support is too bulky or confusing individuals can 
>>cherry pick items they want and make their own simpler target.
>
>The approach used in coide is quite interesting. Have a look on coocox.org. They 
>have it down to box ticking.
>
>> 
>> Actually what we definitely need here in the near term is an arm generic target 
>>and a thumb2 generic target that does not have any of the vendor specific items 
>>in it, perhaps not even core specific peripherals.
>
>I agree.
>
>> 
>> I understand this is a work in progress and sorting everything out will take 
>>some time.
>
>Unfortunately the discussion is rather torn between the basic simplicity camp 
>and the portmanteau camp. I rather think the latter is more suitable for a 
>commercial company which can afford the maintenance, otherwise it is always 
>out-of-date. Keeping up with new ARM cores is perhaps enough to do already.
>
>Geoffrey.
>
>> 
>> David
>> 
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