6502/erc-c
1
0
Fork 0
mirror of https://github.com/pevans/erc-c.git synced 2024-11-27 20:51:17 +00:00
Code Issues Projects Releases Wiki Activity

Some soft switches now require consecutive reads

Browse Source 
To allow this to work, we had to allow the CPU struct to record what the
last opcode/operand/address were, although in truth we only needed the
last address.
This commit is contained in:
Peter Evans 2018-01-12 14:49:27 -06:00
parent 7d6886a3a8
commit f69454c965
4 changed files with 79 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
include/mos6502.h
View File

@ -61,7 +61,7 @@ typedef struct {
vm_segment *wmem;
/*
* This contains the last _effective_ address we've resolved in one
* This contains the _effective_ address we've resolved in one
* of our address modes. In absolute mode, this would be the literal
* operand we read from memory; in indirect mode, this will be the
* address we _find_ after dereferencing the operand we read from
@ -70,6 +70,16 @@ typedef struct {
*/
vm_16bit eff_addr;
/*
* These are the last opcode and last effective address that was
* used in the instruction previous to the one currently being
* executed. Some things (notably soft switches) may need to
* the last opcode.
*/
vm_8bit last_opcode;
vm_8bit last_operand;
vm_16bit last_addr;
/*
* Our program counter register; this is what we'll use to determine
* where we're "at" in memory while executing opcodes. We use a
@ -127,6 +137,7 @@ extern vm_16bit mos6502_pop_stack(mos6502 *);
extern vm_8bit mos6502_get(mos6502 *, size_t);
extern void mos6502_execute(mos6502 *);
extern void mos6502_free(mos6502 *);
extern void mos6502_last_executed(mos6502 *, vm_8bit *, vm_8bit *, vm_16bit *);
extern void mos6502_modify_status(mos6502 *, vm_8bit, vm_8bit);
extern void mos6502_push_stack(mos6502 *, vm_16bit);
extern void mos6502_set(mos6502 *, size_t, vm_8bit);

23
src/apple2.mem.c
View File

@ -179,9 +179,14 @@ apple2_mem_init_sys_rom(apple2 *mach)
SEGMENT_READER(apple2_mem_read_bank_switch)
{
apple2 *mach;
vm_16bit last_addr;
mach = (apple2 *)_mach;
// We need to know the last opcode and address, because some of our
// soft switches require two consecutive reads
mos6502_last_executed(mach->cpu, NULL, NULL, &last_addr);
switch (addr) {
// The $C080 - $C083 range all control memory access while using
// bank 2 RAM for the $Dnnn range. Note that here and in the
@ -194,15 +199,19 @@ SEGMENT_READER(apple2_mem_read_bank_switch)
return 0;
case 0xC081:
apple2_set_bank_switch(mach,
MEMORY_ROM | MEMORY_WRITE | MEMORY_RAM2);
if (last_addr == addr) {
apple2_set_bank_switch(mach,
MEMORY_ROM | MEMORY_WRITE | MEMORY_RAM2);
}
return 0;
case 0xC082:
apple2_set_bank_switch(mach, MEMORY_ROM | MEMORY_RAM2);
return 0;
case 0xC083:
apple2_set_bank_switch(mach, MEMORY_WRITE | MEMORY_RAM2);
if (last_addr == addr) {
apple2_set_bank_switch(mach, MEMORY_WRITE | MEMORY_RAM2);
}
return 0;
// Conversely, the $C088 - $C08B range control memory access
@ -214,7 +223,9 @@ SEGMENT_READER(apple2_mem_read_bank_switch)
return 0;
case 0xC089:
apple2_set_bank_switch(mach, MEMORY_ROM | MEMORY_WRITE);
if (last_addr == addr) {
apple2_set_bank_switch(mach, MEMORY_ROM | MEMORY_WRITE);
}
return 0;
case 0xC08A:
@ -222,7 +233,9 @@ SEGMENT_READER(apple2_mem_read_bank_switch)
return 0;
case 0xC08B:
apple2_set_bank_switch(mach, MEMORY_WRITE);
if (last_addr == addr) {
apple2_set_bank_switch(mach, MEMORY_WRITE);
}
return 0;
// Return high on the 7th bit if we're using bank 2 memory

28
src/mos6502.c
View File

@ -392,10 +392,38 @@ mos6502_execute(mos6502 *cpu)
// something.
usleep(cycles * 10000);
// We need to record the opcode and the effective address for
// anything which might need to reference it.
cpu->last_opcode = opcode;
cpu->last_addr = cpu->eff_addr;
cpu->last_operand = operand;
// Ok -- we're done! This wasn't so hard, was it?
return;
}
/*
* Given pointers for an opcode, operand, and effective address, set the
* dereferenced values of those pointers to what the CPU knows to have
* been the last of each.
*/
void
mos6502_last_executed(mos6502 *cpu, vm_8bit *opcode,
vm_8bit *operand, vm_16bit *addr)
{
if (opcode) {
*opcode = cpu->last_opcode;
}
if (operand) {
*operand = cpu->last_operand;
}
if (addr) {
*addr = cpu->last_addr;
}
}
/*
* Return true if the given instruction would require that we jump
* to somewhere else in the program.

21
tests/apple2.mem.c
View File

@ -134,19 +134,40 @@ Test(apple2_mem, read_bank_switch)
{
vm_segment_get(mach->main, 0xC080);
cr_assert_eq(mach->bank_switch, MEMORY_RAM2);
// This (and a few others) are trickier to test, as they require
// consecutive reads to trigger.
vm_segment_get(mach->main, 0xC081);
cr_assert_neq(mach->bank_switch, MEMORY_ROM | MEMORY_WRITE | MEMORY_RAM2);
mach->cpu->last_addr = 0xC081;
vm_segment_get(mach->main, 0xC081);
cr_assert_eq(mach->bank_switch, MEMORY_ROM | MEMORY_WRITE | MEMORY_RAM2);
vm_segment_get(mach->main, 0xC082);
cr_assert_eq(mach->bank_switch, MEMORY_ROM | MEMORY_RAM2);
// Another that needs consecutives
vm_segment_get(mach->main, 0xC083);
cr_assert_neq(mach->bank_switch, MEMORY_WRITE | MEMORY_RAM2);
mach->cpu->last_addr = 0xC083;
vm_segment_get(mach->main, 0xC083);
cr_assert_eq(mach->bank_switch, MEMORY_WRITE | MEMORY_RAM2);
vm_segment_get(mach->main, 0xC088);
cr_assert_eq(mach->bank_switch, 0);
vm_segment_get(mach->main, 0xC089);
cr_assert_neq(mach->bank_switch, MEMORY_ROM | MEMORY_WRITE);
mach->cpu->last_addr = 0xC089;
vm_segment_get(mach->main, 0xC089);
cr_assert_eq(mach->bank_switch, MEMORY_ROM | MEMORY_WRITE);
vm_segment_get(mach->main, 0xC08A);
cr_assert_eq(mach->bank_switch, MEMORY_ROM);
vm_segment_get(mach->main, 0xC08B);
cr_assert_neq(mach->bank_switch, MEMORY_WRITE);
mach->cpu->last_addr = 0xC08B;
vm_segment_get(mach->main, 0xC08B);
cr_assert_eq(mach->bank_switch, MEMORY_WRITE);