64 lines
1.5 KiB
C
64 lines
1.5 KiB
C
#include <stdio.h>
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/*
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At the moment, this only emulates enough of the IWM to make the Plus boot.
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*/
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#define IWM_CA0 (1<<0)
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#define IWM_CA1 (1<<1)
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#define IWM_CA2 (1<<2)
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#define IWM_LSTRB (1<<3)
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#define IWM_ENABLE (1<<4)
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#define IWM_SELECT (1<<5)
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#define IWM_Q6 (1<<6)
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#define IWM_Q7 (1<<7)
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int iwmLines, iwmModeReg, iwmHeadSel;
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void iwmAccess(unsigned int addr) {
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if (addr&1) {
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iwmLines|=(1<<(addr>>1));
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} else {
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iwmLines&=~(1<<(addr>>1));
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}
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}
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void iwmWrite(unsigned int addr, unsigned int val) {
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iwmAccess(addr);
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int reg=iwmLines&(IWM_Q7|IWM_Q6);
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if (reg==0xC0) iwmModeReg=val;
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// printf("IWM write %x (iwm reg %x) val %x\n", addr, reg, val);
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}
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void iwmSetHeadSel(int s) {
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iwmHeadSel=s;
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}
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unsigned int iwmRead(unsigned int addr) {
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unsigned int val=0;
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iwmAccess(addr);
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int reg=iwmLines&(IWM_Q7|IWM_Q6);
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if (reg==0) {
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//Data register
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val=0;
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} else if (reg==IWM_Q6) {
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//Status register
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int iwmSel=iwmLines&(IWM_CA0|IWM_CA1|IWM_CA2);
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if (iwmHeadSel) iwmSel|=IWM_SELECT; //Abusing this bit for the separate VIA-controlled SEL line
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if (iwmSel==IWM_SELECT) val|=0x80; //No disk in drive.
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if (iwmLines&IWM_ENABLE) val|=0x20; //enable
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val|=iwmModeReg&0x1F;
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// printf("Read disk status %x\n", iwmLines);
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} else if (reg==IWM_Q7) {
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//Read handshake register
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val=0xC0;
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} else {
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//Mode reg?
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if (iwmLines&IWM_ENABLE) val|=0x20; //enable
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val|=iwmModeReg&0x1F;
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}
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// printf("IWM read %x (iwm reg %x) val %x\n", addr, reg, val);
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return val;
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}
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