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riscii: Improve offset calculation for TBRD (nw)

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This commit is contained in:
AJR 2019-09-13 13:44:21 -04:00
parent a06f9b74f6
commit 547828756f
2 changed files with 10 additions and 3 deletions
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12
src/devices/cpu/rii/riscii.cpp
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@ -384,6 +384,11 @@ u16 riscii_series_device::get_banked_address(u8 reg)
return reg;
}
u32 riscii_series_device::tabptr_offset(int offset) const
{
return (m_tabptr & 0x800000) | ((m_tabptr + offset) & ((1 << (m_prgbits + 1)) - 1));
}
//**************************************************************************
// EXECUTION CORE
@ -1053,6 +1058,7 @@ void riscii_series_device::execute_cycle1(u16 opcode)
void riscii_series_device::execute_tbrd(u32 ptr)
{
// TODO: "Bit 23 is used to select the internal/external memory"
u16 addr = get_banked_address(m_curreg);
u16 data = m_program->read_word(ptr >> 1);
if (BIT(ptr, 0))
@ -1092,15 +1098,15 @@ void riscii_series_device::execute_run()
break;
case EXEC_TBRD1:
execute_tbrd(m_tabptr++);
execute_tbrd(std::exchange(m_tabptr, tabptr_offset(1)));
break;
case EXEC_TBRD2:
execute_tbrd(m_tabptr--);
execute_tbrd(std::exchange(m_tabptr, tabptr_offset(-1)));
break;
case EXEC_TBRDA:
execute_tbrd(m_tabptr + m_acc);
execute_tbrd(tabptr_offset(m_acc));
break;
case EXEC_L0JMP: case EXEC_L1JMP: case EXEC_L2JMP: case EXEC_L3JMP:

1
src/devices/cpu/rii/riscii.h
View File

@ -95,6 +95,7 @@ private:
// memory helpers
u16 get_banked_address(u8 reg);
u32 tabptr_offset(int offset) const;
// execution
void execute_move(u8 dstreg, u8 srcreg);