[fpc-devel] Freepascal in microcontrollers

[Vinzent Hoefler]

On Wednesday 27 February 2008 11:45, Florian Klaempfl wrote:
> Vinzent Hoefler schrieb:
> > On Wednesday 27 February 2008 11:16, Micha Nelissen wrote:
> >> Vinzent Hoefler wrote:
> > If I mean to set the write buffer water mark of the SDRAM
> > controller
> >
> > register, I'd rather write:
> > |SDRAM_Buffer_Control.WB_Watermark := Sixteen;
> >
> > instead of
> >
> > |SDRAMBufferControl := (SDRAMBufferControl and not
> > | WB_WATERMARK_MASK) or WB_WATER_MARK_16;
>
> I don't see the point: pascal and also fpc know bitpacked records?

Well, TP didn't, and until now I found no real documentation on it (it 
sure wasn't mentioned in *my* copy of the programmer's manual). If it's 
similar to C-records then it's unusable anyway, as there are no 
guarantees. Not about endianess, not about padding. And what about 
volatile and/or atomic semantics?

Well, too many question at once. I boil it down to this one: How else do 
you write it? The original layout declaration:

|  for SDRAM_Buffer_Control use
|   record
|      WB           at 0 range 0 .. 0;
|      WB_Flush     at 0 range 1 .. 1;
|      WB_Watermark at 0 range 2 .. 3;
|      Read_Ahead   at 0 range 4 .. 4;
|      --  bits [5:7] are reserved
|   end record;

It get's especially tricky, because in many cases the bit patterns don't 
fit the numbers:

|  type RAS_CAS_Delay is range 2 .. 4;
|  for  RAS_CAS_Delay'Size use 2;

or

|  type CAS_Latency is range 2 .. 3;
|  for  CAS_Latency'Size use 1;

I don't really want to write

|SDRAM_Timing_Control.CAS_Latency := 1; // Where 0 is 2 and 1 is 3.

Well, not that big a problem, because once the patterns get 
nonconsecutive, you'd need enums either way. ;)


Vinzent.