Dear Remco Poelstra,
In message 499AA5B8.7030805@duran-audio.com you wrote:
I'm trying to get my LPC2468 based board to work. I've some problems with the external memory databus. I would like to know the settings of internal registers to see whether I've initialized them correctly, so I tried making a function that prints the content over the serial link. I'm still in the lowlevel_init function, so I do not have the U-boot puts functions available. I wrote the following function to convert a long to a HEX string:
void print_long(unsigned long data) { char i; char hex_data[]={'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
for(i=0; i<8; i++) { while((U0LSR & (1<<5)) == 0); /* Wait for empty U0THR */ // U0THR = hex_data[(0xDEADBEEF>>i*4)&0xF];
For clearity of the code I would write that as "...>>(i*4)...", but that's not relevant here.
U0THR = hex_data[(0xDEADBEEF>>4)&0xF];} }
When I run it likes this I get 8 E's. Which is what I expect. When I run it with the commented-out line, I get back 8 0x0's. So it seems that the output is only correct when it is constant. Does anyone have a clue on why that is?
What exactly is U0THR ?
The only definition I can find in the U-Boot sources is here:
include/asm-arm/arch-lpc2292/lpc2292_registers.h:#define U0THR 0xE000C000
but that is obviously not what you are using.
You probably forget the effects of compiler optimization and/or caching here.
I bet you are using a plain pointer access without a "volatile", which is essential here. Maybe even some form of "sync" is needed. In any case, you should use appropriate accessor functions to access device registers.
Best regards,
Wolfgang Denk