[fpc-devel] Arm Thumb2 - Stellaris status

[Geoffrey Barton]

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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