apple2a/platform.c

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C
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#include "platform.h"
2018-08-03 01:59:31 +00:00
#define KBD_STATUS_OR_KEY ((unsigned char *)0xC000)
#define KBD_CLEAR_CURRENT_KEY ((unsigned char *)0xC010)
#define KEY_READY_MASK 0x80
#define KEY_VALUE_MASK 0x7F
// Returns non-zero if a key is ready to be read.
int keyboard_test(void)
{
return *KBD_STATUS_OR_KEY & KEY_READY_MASK;
}
// Clears current key, sets up next one for test or get
void keyboard_clear(void)
{
unsigned char clear_key;
// On 6502, a write cycle READS AND THEN WRITES, so just read the
// "latch next key" strobe.
clear_key = *KBD_CLEAR_CURRENT_KEY;
}
// Wait until a key is ready and then return it without high bit set
unsigned char keyboard_get(void)
{
unsigned char key;
while(!((key = *KBD_STATUS_OR_KEY) & KEY_READY_MASK));
keyboard_clear();
return key & KEY_VALUE_MASK;
}