mirror of https://github.com/pevans/erc-c.git
80 lines
2.6 KiB
C
80 lines
2.6 KiB
C
/*
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* apple2.kb.c
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*
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* Handle soft switches to read keyboard state, which are surprisingly
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* few and lightweight. The state would be the last key pressed, whether
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* a key is pressed _right now_, and the keyboard strobe (which is used
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* to determine if you've read last key pressed before or not).
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*/
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#include "apple2/kb.h"
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/*
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* This mapper is considerably simpler than most, because it handles
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* only two addresses and only read maps. It merely performs the mapping
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* for keyboard switches.
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*/
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void
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apple2_kb_map(vm_segment *seg)
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{
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vm_segment_read_map(seg, 0xC000, apple2_kb_switch_read);
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vm_segment_read_map(seg, 0xC010, apple2_kb_switch_read);
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}
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/*
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* This mapper handles reads to switches that report info on the
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* keyboard state. Note that there is no write switch function; there
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* are only reads that need to be handled.
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*/
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SEGMENT_READER(apple2_kb_switch_read)
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{
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apple2 *mach = (apple2 *)_mach;
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char ch = '\0';
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switch (addr) {
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case 0xC000:
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// This _also_ returns the 7 bit high if the strobe is still
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// set. Once you read from $C010, this bit will be cleared
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// in future reads--until another key is pressed.
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if (mach->screen) {
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ch = vm_screen_last_key(mach->screen);
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// If the strobe is set, we need to set the 7 bit on the
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// return value. (NOTE: Apple II can only handle 7-bit
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// ASCII, so the highest bit (bit 7, if counting from
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// zero) is always low in regards to ASCII
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// representation; it can _only_ be high if the strobe
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// is set.
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if (mach->strobe) {
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return ch | 0x80;
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}
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}
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// If we have no screen, we'll just end up returning
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// whatever is in ch already (NUL).
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return ch;
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case 0xC010:
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// First, we need to clear the keyboard strobe.
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mach->strobe = false;
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if (mach->screen) {
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// Now we need to return whether any key was pressed, but
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// we'll have to ask the vm_screen subsystem. We just want
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// to return with the 7 bit high if it is pressed, and all
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// zeroes if not.
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return vm_screen_key_pressed(mach->screen)
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? 0x80
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: 0x00;
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}
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// We have no keyboard, so we basically can have no key
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// pressed down.
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return 0;
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}
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// This can only happen if we were mapped to an address we weren't
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// prepared to handle
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return 0;
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}
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