[LLVMdev] 答复: [LLVMdev] How to bind a register variable with a given general purpose register?

[ether]

hi zhu,

i am not sure if your c frontend support "int ADC asm("GPR13");"
i think you could:

1. add a attribute "GPR13"(or a more meaningful name like "adcreg") and
the corresponding handler, so you code "int ADC asm("GPR13");" became
"int ADC __attribute__((GPR13));"
2. add a intrinsic functions like "llvm.zhu.readadcreg()".
3. map any read to the variable marked with __attribute__((GPR13)) to
llvm.zhu.readadcreg() instead of "load" instruction
4. assign gpr13 to a special register class like "gpr13class" instead of
gprclass, so gpr13 will not be allocated as other gpr.
5. lower instrinisic functions "llvm.zhu.readadcreg()" to register node
"gpr13" in your backend.

regards

--ether

On 2010-1-4 18:01, Demon(Xiangyang) Zhu 朱向阳 wrote:
> Hi Ether,
>
> The hardware had been fixed now. 
> If map it to memory space, it will cost another instruction cycle to execute 'a = ADCREG',
> Algorithm accesses the A/D convert very frequently. To get higher precision at lower frequency 
> A/D output is connected to R13 directly. For the moment algorithm code is something like 
> assemble and difficult to maintain.  I want to setup a c environment for it, but i don't know 
> how to  bind a register variable with a given general purpose register.
>
> Thanks!
>
> ________________________________________
> 发件人: llvmdev-bounces at cs.uiuc.edu [llvmdev-bounces at cs.uiuc.edu] 代表 ether [etherzhhb at gmail.com]
> 发送时间: 2010年1月4日 0:36
> 收件人: llvmdev at cs.uiuc.edu
> 主题: Re: [LLVMdev] How to bind a register variable with a given general purpose register?
>
> hi zhu,
>
> i think you should map the peripheral registers to data memory space
> instead of register file, then mark that memory address as "volatile".
> like said the adc register was mapped to address 0xc0000, and then the
> corresponding c source will goes like this:
> //define the register
> #define ADCREG (*((volatile unsigned int *)0xc0000))
> //read the register
> a = ADCREG
>
> --ether
>
> On 2010-1-4 10:59, Heyu Zhu wrote:
>   
>> Hi everyone,
>> There are 16 GPRs in my RISC, but in fact GPR13 is read-only and
>> connected to output of an A/D converter.
>> It would be very convenient if i could bind a register variable with
>> GPR13.
>> Because i am a newbie i don't know how my llvm backend can support that.
>> I plan to implement it as below.
>> A. first declare a global variable in c-code
>> int ADC asm("GPR13");
>> B. If backend finds a variable is loaded from "GPR13" use GPR13 instead.
>> C. backend can't allocate GPR13 to other variable
>> Is it a foolish method? Is there a better one? Please give me some
>> guidance
>> Thanks
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>     
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev