38 lines
1.3 KiB
C
38 lines
1.3 KiB
C
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#pragma once
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#include "emul.h"
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/* Emulates the behavior of an AT28 EEPROM. When reading, behaves like regular
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* RAM. When writing, be in "writing mode" for 10ms. If we assume 8MHz, that
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* means 80k t-states tracked from the CPU.
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*
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* While we're in programming mode, reading the written address will emulate
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* the "polling mode" of the AT28, that is, each read toggles IO/6.
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*
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* If another write happens before we're done writing or if we read from another
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* address, writing fails (both the new write and the old one) and nothing is
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* written to memory.
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*/
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typedef struct {
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// CPU reference needed to keep track of time
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Z80Context *cpu;
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// only range startoffset:size is used
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byte mem[LEN16BIT];
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// offset at which the EEPROM begins
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ushort startoffset;
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// EEPROM size
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ushort size;
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// t-state stamp of the active writing operation. 0 means none.
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unsigned int wrstamp;
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// address being written to
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ushort wraddr;
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// byte being written
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byte wrval;
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// last polled value. Next polling will yield this value with 6th bit
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// toggled.
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byte pollval;
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} AT28;
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void at28_init(AT28 *at28, Z80Context *cpu, ushort startoffset, ushort size);
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byte at28_mem_read(AT28 *at28, ushort addr);
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void at28_mem_write(AT28 *at28, ushort addr, byte val);
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