[U-Boot-Users] Spartan FPGA patch

[Aggelos Manousarides <amanous@inaccessnetworks.com>]

Wolfgang Denk wrote:
> In message <472F1393.7040306@inaccessnetworks.com> you wrote:
>> Wolfgang Denk wrote:
>>> In message <472752F9.9000307@inaccessnetworks.com> you wrote:
>>>> The following patch fixes a bug in the slave serial programming mode for 
>>>> the xilinx spartan2 FPGA. A "char val" is declared, but it is used as a 
>>>> signed char. The check for negative value (<0) is always true on arm, or 
>>>> any other platform in which the char is not signed by default. As a 
>>>> result the FPGA cannot be programmed.
>>> I have to admit that I hate to see "signed  char"  in  the  code.  Is
>>> there  any  special  reaso why "val" has to be a "char" type? Why not
>>> making it an "int" ?
>> Another way to do this safely is to declare it as an "unsigned char" and 
>> instead of doing "val < 0", do "val & 0x80". I don't like the current 
>> code either. Shifting a signed char and testing for negativity is 
>> definitely not the best way to test that the MSB is set.
> 
> So let me repeat my question: is there any special reason  why  "val"
> has to be a "char" type? Why not making it an "int" ?

Because you will run into endianness problems. You want to treat an 
"unsigned char" buffer as a bitstream, reading the MSB every time. How 
are you going to do this portably (in both big and little endian 
architectures) with an "int" type, which is at least 2 bytes wide?

--
Angelos Manousaridis