Lpc2000

Oooops! Sorry, your are right!

  Sten

Yannick Hildenbrand wrote:
> Hello,
> 
>  
> 
> I just would like to add a small remark to this excellent analysis
> 
>  
> 
> The BLX instruction is available on architectures V5 and above (see the
> Addison-Wesley ARM Architecture Reference Manual). The LPC 2000 family uses
> the V4T architecture, and this means that BLX cannot be used. Be careful
> when specifying the core variant in the assembler argument list. If the
> right architecture is not correctly specified (or the default is e.g. V5 or
> above), the assembler may accept BLX but the code may have strange behavior
> on a LPC2000. Double checking this may avoid long hours of debugging.
> 
>  
> 
> Cheers.
> 
>  
> 
> Duke
> 
>  
> 
> 
> De : lpc2000@yahoogroups.com [mailto:lpc2000@yahoogroups.com] De la part de
> Sten
> Envoy\ufffd : lundi 17 octobre 2005 20:28
> \ufffd : lpc2000@yahoogroups.com
> Objet : Re: [lpc2000] ARM mode
> 
>  
> 
> Hello,
> 
> entry of interrupts must be compiled in ARM mode. If you return from a
> function or interrupt by LR (return address in link register) you do not
> need to take care about ARM&Thumb. If you want to jump to a Thumb
> function from ARM mode you can use a these instructions
> 
>       bx ip            ;Branch (simple jump)
>       blx label      ;Branch with link register (call subfuction)
> 
> All addresses have an even value due to its 32bit (ARM) or 16bit (Thumb)
> instruction length. But if you branch to an odd address
> (destination_addr + 1) the ARM core will enter Thumb state. If the
> address is even it will assume that the code is in ARM mode
> 
>       /* ARM mode */
> 1000:      ...
> 1004:      blx 2001      ;Call sub-function "subfunc" @0x2000
> 1008:      ...
> 
>       /* Thumb mode */
> subfunc:
> 2000:      push {r4, lr}      ;LR = 0x1008 (even: this was ARM mode)
>       ...
> 2010:      pop {r4}
> 2012:      pop {r0}      ;R0 = LR
> 2014:      bx r0            ;return (and enter ARM mode again)
> 
> -------------------------------------------------------------
>       /* Thumb mode */
> 1000:      ...
> 1002:      blx 2001      ;Call sub-function "subfunc" @0x2000
> 1004:      ...
> 
>       /* Thumb mode */
> subfunc:
> 2000:      push {r4, lr}      ;LR = 0x1005 (odd: this was Thumb mode)
>       ...
> 2010:      pop {r4}
> 2012:      pop {r0}      ;R0 = LR
> 2014:      bx r0            ;return (and stay in Thumb mode again)
> 
> See the ARM7TDMI technical reference manual for details.
> 
> When using GNU gcc don't forget to compile your gcc with the feature
> 'thumb-interworking' and all objects of your project with the command
> line option '--mthumb-interwork'.
> 
>    Sten
> 
> Tom Walsh wrote:
> 
>>wiese_matthias wrote:
>>
>>
>>
>>>Hi,
>>>we are programming a lpc2294 and have problems with the ARM/THUMB mode.
>>>We'd like to use the mixed mode (arm & thumb mode) to save time
>>>loading the programs from a 16-Bit flash memory. Unfortunately the
>>>program get stucked if an interrupts occurs when we are using the
>>>mixed mode. With the arm mode everything works fine.
>>>Can someone tell us how we can also work in the thumb mode?
>>>Thank you!
>>>Matthias
>>>
>>>
>>>
>>>
>>
>>I was just reading something about that up at arm.com.  Something about 
>>having interrupt handlers written / compiled in thumb.  IIRC, the ARM 
>>processors start in ARM mode, then you have to "BX" them into thumb 
>>mode.  Same thing with the Interrupts, the interrupts entry is in ARM 
>>mode of operation, so you have to enter & leave the handlers properly.
>>
>>IIRC, Chapter 7 explains this: SDT2.50 User Guide 
>><http://www.arm.com/pdfs/sdt250usrman.pdf>
>>
>>I looked at thumb, I'm not ready to mess with interworking yet.
>>
>>TomW
>>
> 
> 
> 


-- 
/************************************************
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