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Merge pull request #25 from markadev/reset-detection
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Improve reset detection
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@markadev
markadev authored Dec 10, 2023
2 parents 400334f + 80958da commit 7c52263
Showing 1 changed file with 94 additions and 66 deletions.
160 changes: 94 additions & 66 deletions pico/abus.c
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ enum {
typedef void (*shadow_handler)(bool is_write, uint_fast16_t address, uint_fast8_t data);


static int reset_detect_state = 0;
static unsigned int char_write_offset;
static shadow_handler softsw_handlers[128];

Expand Down Expand Up @@ -245,84 +246,111 @@ static void __time_critical_func(device_write)(uint_fast8_t reg, uint_fast8_t da
}


// Shadow parts of the Apple's memory by observing the bus write cycles
static void __time_critical_func(shadow_memory)(bool is_write, uint_fast16_t address, uint32_t value) {
// Shadow parts of the Apple's memory by observing the bus write cycles
static bool reset_phase_1_happening = false;

// Mirror Video Memory from MAIN & AUX banks
if(address < 0xc000) {
reset_phase_1_happening = false;
uint8_t *bank;

switch((address & 0xfc00) >> 10) {
case 0x0400 >> 10:
// text page 1
reset_detect_state = 0;
if(!is_write)
return;
break;

// Refer to "Inside the Apple IIe" p.295 for how Aux memory addressing is done
if((address >= 0x400) && (address < 0x800)) {
// text page 1
uint8_t *bank;
if(soft_80store) {
// 80STORE takes precedence - bank is then controlled by the PAGE2 switch
bank = (soft_switches & SOFTSW_PAGE_2) ? aux_memory : main_memory;
} else if(soft_ramwrt) {
bank = aux_memory;
} else {
bank = main_memory;
}
bank[address] = value & 0xff;
} else if((address >= 0x800) && (address < 0xc00)) {
// text page 2
uint8_t *bank = soft_ramwrt ? aux_memory : main_memory;
bank[address] = value & 0xff;
} else if((address >= 0x2000) && (address < 0x4000)) {
// hires page 1
uint8_t *bank;
if(soft_80store && (soft_switches & SOFTSW_HIRES_MODE)) {
// 80STORE takes precedence - bank is then controlled by the PAGE2 switch
bank = (soft_switches & SOFTSW_PAGE_2) ? aux_memory : main_memory;
} else if(soft_ramwrt) {
bank = aux_memory;
} else {
bank = main_memory;
}
bank[address] = value & 0xff;
} else if((address >= 0x4000) && (address < 0x6000)) {
// hires page 2
uint8_t *bank = soft_ramwrt ? aux_memory : main_memory;
bank[address] = value & 0xff;
if(soft_80store) {
// 80STORE takes precedence - bank is then controlled by the PAGE2 switch
bank = (soft_switches & SOFTSW_PAGE_2) ? aux_memory : main_memory;
} else if(soft_ramwrt) {
bank = aux_memory;
} else {
bank = main_memory;
}
bank[address] = value & 0xff;
break;

return;
}
case 0x0800 >> 10:
// text page 2
reset_detect_state = 0;
if(!is_write)
break;

bank = soft_ramwrt ? aux_memory : main_memory;
bank[address] = value & 0xff;
break;

// Handling shadowing of the soft switches in the range 0xc000 - 0xc07f
if(address < 0xc080) {
reset_phase_1_happening = false;
case 0x2000 >> 10 ... 0x3c00 >> 10:
// hires page 1
reset_detect_state = 0;
if(!is_write)
break;

shadow_handler h = softsw_handlers[address & 0x7f];
if(h) {
h(is_write, address, value & 0xff);
if(soft_80store && (soft_switches & SOFTSW_HIRES_MODE)) {
// 80STORE takes precedence - bank is then controlled by the PAGE2 switch
bank = (soft_switches & SOFTSW_PAGE_2) ? aux_memory : main_memory;
} else if(soft_ramwrt) {
bank = aux_memory;
} else {
bank = main_memory;
}
return;
}
bank[address] = value & 0xff;
break;

// Reset detection
if((address == 0xfffc) && !is_write) {
reset_phase_1_happening = true;
} else if((address == 0xfffd) && !is_write && reset_phase_1_happening) {
// Reset soft-switches
soft_switches = SOFTSW_TEXT_MODE;
soft_video7_mode = VIDEO7_MODE_140x192;
soft_dhires = false;
soft_80col = false;
soft_80store = false;
soft_altcharset = false;
soft_ramwrt = false;
case 0x4000 >> 10 ... 0x5c00 >> 10:
// hires page 2
reset_detect_state = 0;
if(!is_write)
break;

bank = soft_ramwrt ? aux_memory : main_memory;
bank[address] = value & 0xff;
break;

reset_phase_1_happening = false;
} else {
// FIXME: this case should execute every time any address != 0xfffd is
// seen, otherwise it gets "stuck" as true for any number of machine cycles
reset_phase_1_happening = false;
case 0xc000 >> 10:
reset_detect_state = 0;

// Handle shadowing of the soft switches in the range 0xc000 - 0xc07f
if(address < 0xc080) {
shadow_handler h = softsw_handlers[address & 0x7f];
if(h) {
h(is_write, address, value & 0xff);
}
}
break;

case 0x0000 >> 10:
case 0xfc00 >> 10:
// reset detection - the IOU chip on the Apple IIe cleverly detects a CPU reset by monitoring bus activity
// for a sequence usually only seen when the CPU resets: three page 1 accesses followed by an access to
// address $FFFC (see "Understanding the Apple IIe" pages 4-14 and 5-29).
if((address >> 8) == 0x01) {
// count the consecutive page 1 accesses, up to 3
if(reset_detect_state < 3) {
reset_detect_state++;
} else if(reset_detect_state > 3) {
reset_detect_state = 1;
}
} else if((reset_detect_state == 3) && (address == 0xfffc)) {
reset_detect_state++;
} else if((reset_detect_state == 4) && (address == 0xfffd)) {
// reset soft-switches
soft_switches = SOFTSW_TEXT_MODE;
soft_video7_mode = VIDEO7_MODE_140x192;
soft_dhires = false;
soft_80col = false;
soft_80store = false;
soft_altcharset = false;
soft_ramwrt = false;

reset_detect_state = 0;
} else {
reset_detect_state = 0;
}
break;

default:
reset_detect_state = 0;
break;
}
}

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