Re: [Fx2lib-devel] Setupdata at 0xe000

[Maarten B. <sou...@ds...>]

Hi,

Daniel wrote:
> I think it probably "just works" in this case because the descriptor
> table is defined in assembly and its address is forced in the linker. 
> 
> Hence the declaration only affects how the C code accesses it. 

Ah yes, I forgot about this.

Chris wrote;
> You're the last person in the world I would want to argue with about
> SDCC, but my observations *appear* to contradict you:

It works because the descriptors are initialized in assembly.

> * xdata is initialised with explicit values at 0x3f00 and 0xe000 by the
> RAM load and 0xC2 EEPROM load before any SDCC-generated code executes
> 
> > > FWIW, I just tried the code->xdata + DSCR_AREA=e000 change on the
> > > firmware in FPGALink[2] and it works fine.
> > 
> > Are you using C0 or C2 mode? C2 mode cannot load 0xe000 
> > according to the datasheet. Can the driver download to 
> > 0xe000 directly?
> > 
> A 0xC2 loader can definitely target 0xe000. There's a note in section
> 3.4.3 of the TRM:
> 
> Serial EEPROM data can be loaded only into these three on-chip RAM
> spaces:
> * Program / Data RAM at 0x0000-0x1FFF
> * Data RAM at 0xE000-0xE1FF
> * The CPUCS register at 0xE600 [bit 0]
> 
> (Actually the TRM is a bit wrong here because it can actually load
> program/data RAM at 0x0000-0x3fff, not 0x0000-0x1fff, but the point
> about 0xe000-0xe1ff stands).

I admit I did not read further than 3.2 EZ-USB Startup Modes which 
states:
Note: Although the EZ-USB can perform C2 Loads from EEPROMs as large 
as 64 KB, code can only be downloaded to the 16K of on chip RAM.

On second thought I think "code" here means code space since 0xe000 
is xdata only. I had read it as 'binary data'.

Sorry for the noise,
Maarten