I think you need to refer COM3 (0x0100) in reference to ES (Extra Segment) register.
You first copy 0x00 to es register and then refer in COM3 inrelation to es, bye es:COM3
I don't know the syntax of Linux Assmbly, but I hope you got my point.
I think you need to add following code before refering COM3
movl $(0x00) %eax
movl %eax %es
After refering refer COM3 in reference to es register.
I might be wrong, if I am wrong please correct me.
Regards,
Gaurav
No, no,
Linux works on protected mode. You cannot load segment registers as in real mode. In protected mode, They are called selecters which select the GDT entry. In kernel mode (Linux), segment registers are always (cs=0x08 and ds,es,fs,gs... = 0x10) and in user mode (cs= 0x23 ds,es,fs,gs...=0x2b).
I am trying to to set up my ports for IO with the low level inb() and outb() in the code below. However, as soon as I write to the COM port, I get a segmentation fault. The hardware uses a lava card with 8 COM ports available.
I know that similar code works in module form, whereby I insmod the module, and set up my ports using in the init_module() function. Here, however, I am trying to build it into a regular executable. But is that the reason?
TIA.
Raja Hayek.
The problem is with the I/o permission. If you know about Intels TSS(Task State Segment), It contains a bitmap which decides which i/o address the user can accrss from ring 3. So, first you need to change that using ioperm system call.
see man ioperm
regards manish
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