Lpc2000

--- In lpc2000@yahoogroups.com, "shergtu" <shergtu@...> wrote:
>
> > I have found so far, that by making changes to linker file, RAM  is
> > there available for RD/WR, but C-Spy will *not* show anything but
> > zeros; it treats it as ROM, any overtyped value is ignored.
> > I have downloaded JARM.DLL ver 3.14, replaced my 2.74c, with no
> > difference in behavior. 
> > Is anybody outhere able to see in C-Spy the USB_DMA RAM as RAM? 
> > 
> > I appreciate your feedback. 
> > BTW, EWARM 4.31A is out, have not tested it, yet. 
> > My observations were for ver. 4.30A.
> > 
> > Thanks!
> > 
> > Roger
> 
> Hi Roger,
> 
> Thanks for your input on this too.
> 
> For what it's worth, I'm using Keil / uVision 3 with the ARM 
> development tools, and I only read back zeros as well.
> 
> I first noticed the problem with USB RAM when my code crashed in ISRs 
> while running directly out of flash, no JTAG or debugger at all.
> 
> Turns out the writes to the IRQ stack (i.e. IRQ mode R13 set to point 
> into USB RAM) went into the great bit bucket, so when popping the LR 
> from the stack,  PC = 0x0000.0000 and off we go....

shergtu,
I saw this happening, too; in C-Spy - *all* registers=0x0. But not always.
After an incident like this, it is better to reboot the JTAG and start
again.
 
> (One thing that is frustrating, I guess it was a design choice by the 

Yes, frustrating, but since you see it also in KEIL uV/uLink, I wonder
if it has to do with 2148 only, rather then toolset vendor.

> engineers at Keil -- if in the debugger I modify (for example) memory 
> 0x7FD0.1000 to a value of 0x55, it shows the change -- until I step 
> the next instruction.  Then it changes the displayed value back to 
> 0x00.  Um, is there a reason the value isn't read back by the 
> debugger immediately after it is written, so that what is displayed 
> reflects what is *really* in the memory?  I'm willing to wait the 
> extra few usec/msec for that benefit.  :-)  )

I am about to test whether it is JTAG comm speed sensitive, last straw
that I am grasping....
 
> I was hoping to just "manually" carve/manage the 8K USB RAM block 
> myself for things like task & interrupt stacks, ring buffers, etc...  
> In other words I wanted to avoid scatter/gather linker files, and 
> compile-time locating of structures.... at run time I'll just point 
> into the USB RAM and carve it up.

> I'm actually shocked that no one else has tried to use the USB RAM 
> for something other than USB (at least no one has chimed in that 
> effect).

Yes, that puzzles me too. So many USB design comments around, yet no
one said anything about this USB RAM "invisibility". 
Hm.
 
> I'll keep you posted on what I find.
>

Please do. I promise the same.

Thanks for your comments.

Take care

Roger