All,
I've been using SDCC with good success for about a year; I'm currently using
version 2.7.0. I'm in the process of developing an instrument that includes
two Atmel AT89C51ED2 microprocessors, external UARTs, RS232 to TTL level
converters, ADC, DAC, digital I/O, thermocouple amplifiers, a serial
keypad/LCD, SPI interfaces, etc. I've written all of the C code to drive these
devices, and the entire system works well.
But, I've now run up against a problem that has me stymied. On one of the
microprocessors the current program uses about 255 bytes of XDATA
(XRAM?).--almost all global variables. And this program runs well. Now, I
need to add more features to the program so that the total bytes of XDATA
exceeds 256 bytes. When I do this, my program fails to run. It seems that
most--if not all--of the variables have zero (0) values.
I've read enough on-line about this problem to be dangerous and very confused.
The advice that I've found ranges from that I should use the compiler option
--no-xinit-opt to copy and adapt crtxinit.asm from the library and link it with
my project to implement a custom __sdcc-external_startup program (to all of the
above?). I also see that maybe I should set 3 bits in the AUXR register to
select the proper XRAM size, perhaps set the bit EXTRAM to 0, and maybe change
a bit in the AUXR1 register. I've used --no-xinit-opt and tried various
combinations of bits in the AUXR and AUXR1 registers with no success, but I'm
not sure how to implement the sdcc_external_startup program or how to modify
and link crtxinit.asm. Worse, as I'm sure you can tell by now, I'm not certain
which ones of these multitude of "suggestions" should be implemented.
I don't mind putting in a lot of effort, but it seems the more I dig, the more
confused I've become. Any help on this problem would be appreciated, and I
would be happy to look at other websites or other sources of information that
you think would be helpful.
Thanks for your consideration of my problem!
Gary
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