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Arlet 65C02 WIP: Implement NOPs (optional)

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Change-Id: I96f1f9dd23f201ff017aaf6c2c69ad40ec928ea2
This commit is contained in:
David Banks
2016-08-01 12:01:44 +01:00
parent db83fd4af9
commit bf3dad7af1
1 changed files with 18 additions and 3 deletions
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21
cpu_65c02.v
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@@ -18,6 +18,16 @@
* on the output pads if external memory is required.
*/
/*
* Two things were needed to correctly implement 65C02 NOPs
* 1. Ensure the microcode state machine uses an appropriate addressing mode for the opcode length
* 2. Ensure there are no side-effects (e.g. register updates, memory stores, etc)
*
* If IMPLEMENT_NOPS is defined, the state machine is modified accordingly.
*/
`define IMPLEMENT_NOPS
module cpu_65c02( clk, reset, AB, DI, DO, WE, IRQ, NMI, RDY );
input clk; // CPU clock
@@ -915,6 +925,11 @@ always @(posedge clk or posedge reset)
8'b0110_0000: state <= RTS0;
8'b0110_1100: state <= JMPI0;
8'b0111_1100: state <= JMPIX0;
`ifdef IMPLEMENT_NOPS
8'bxxxx_xx11: state <= REG; // (NOP1: 3/7/B/F column)
8'bxxx0_0010: state <= FETCH; // (NOP2: 2 column, 4 column handled correctly below)
8'bx1x1_1100: state <= ABS0; // (NOP3: C column)
`endif
8'b0x00_1000: state <= PUSH0;
8'b0x10_1000: state <= PULL0;
8'b0xx1_1000: state <= REG; // CLC, SEC, CLI, SEI
@@ -1029,7 +1044,7 @@ always @(posedge clk)
always @(posedge clk)
if( state == DECODE && RDY )
casex( IR )
casex( IR ) // DMB: Checked for 65C02 NOP collisions
8'b0xx1_0010, // ORA, AND, EOR, ADC (zp)
8'b1x11_0010, // LDA, SBC (zp)
8'b0xxx_1010, // ASLA, INCA, ROLA, DECA, LSRA, PHY, RORA, PLY
@@ -1110,7 +1125,7 @@ always @(posedge clk)
always @(posedge clk)
if( state == DECODE && RDY )
casex( IR )
casex( IR ) // DMB: Checked for 65C02 NOP collisions
8'b1001_0010, // STA (zp)
8'b100x_x1x0, // STX, STY, STZ abs, STZ abs,x
8'b011x_0100, // STZ zp, STZ zp,x
@@ -1123,7 +1138,7 @@ always @(posedge clk)
always @(posedge clk )
if( state == DECODE && RDY )
casex( IR )
casex( IR ) // DMB: Checked for 65C02 NOP collisions
8'b0xxx_x110, // ASL, ROL, LSR, ROR
8'b000x_x100, // TSB/TRB
8'b11xx_x110: // DEC/INC