36 lines
1.2 KiB
C
36 lines
1.2 KiB
C
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/**
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* Read a byte from the specified port
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*/
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unsigned char port_byte_in (unsigned short port) {
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unsigned char result;
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/* Inline assembler syntax
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* !! Notice how the source and destination registers are switched from NASM !!
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*
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* '"=a" (result)'; set '=' the C variable '(result)' to the value of register e'a'x
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* '"d" (port)': map the C variable '(port)' into e'd'x register
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*
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* Inputs and outputs are separated by colons
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*/
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__asm__("in %%dx, %%al" : "=a" (result) : "d" (port));
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return result;
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}
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void port_byte_out (unsigned short port, unsigned char data) {
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/* Notice how here both registers are mapped to C variables and
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* nothing is returned, thus, no equals '=' in the asm syntax
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* However we see a comma since there are two variables in the input area
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* and none in the 'return' area
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*/
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__asm__("out %%al, %%dx" : : "a" (data), "d" (port));
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}
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unsigned short port_word_in (unsigned short port) {
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unsigned short result;
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__asm__("in %%dx, %%ax" : "=a" (result) : "d" (port));
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return result;
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}
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void port_word_out (unsigned short port, unsigned short data) {
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__asm__("out %%ax, %%dx" : : "a" (data), "d" (port));
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}
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