diff --git a/src/opcodes.c b/src/opcodes.c index 7ea5150..324fd44 100644 --- a/src/opcodes.c +++ b/src/opcodes.c @@ -77,12 +77,16 @@ void fetch_operand() break; case relative: operand = read_byte(pc); + pc = pc + 1; if ((operand >> 7) == 0) { address = pc + operand; } else { + // negate b operand using 2's complement + operand = operand ^ 0xFF; + operand = operand + 1; address = pc - operand; } break; @@ -131,11 +135,11 @@ void push_byte(db data) void push_word(dw data) { - db high = data & 0xFF; - db low = data >> 8; + db low = data & 0xFF; + db high = data >> 8; - push_byte(high); push_byte(low); + push_byte(high); } db pull_byte() @@ -146,10 +150,9 @@ db pull_byte() dw pull_word() { - dw data; - - data = pull_byte() << 8; - data = data | pull_byte(); + db high = pull_byte() << 8; + db low = pull_byte(); + dw data = high | low; return data; } @@ -192,43 +195,31 @@ void asl() void bcc() { // branch on carry clear + fetch_operand(); if(!C_IS_SET) { - fetch_operand(); pc = address; } - else - { - pc = pc + 1; - } } void bcs() { // branch on carry set + fetch_operand(); if(C_IS_SET) { - fetch_operand(); pc = address; } - else - { - pc = pc + 1; - } } void beq() { // branch on result zero + fetch_operand(); if(Z_IS_SET) { - fetch_operand(); pc = address; } - else - { - pc = pc + 1; - } } void bit() @@ -243,43 +234,31 @@ void bit() void bmi() { // branch on result minus + fetch_operand(); if(N_IS_SET) { - fetch_operand(); pc = address; } - else - { - pc = pc + 1; - } } void bne() { // branch on result not zero + fetch_operand(); if(!Z_IS_SET) { - fetch_operand(); pc = address; } - else - { - pc = pc + 1; - } } void bpl() { // branch on result plus + fetch_operand(); if(!N_IS_SET) { - fetch_operand(); pc = address; } - else - { - pc = pc + 1; - } } void brk() @@ -293,29 +272,21 @@ void brk() void bvc() { // branch on overflow clear + fetch_operand(); if(!V_IS_SET) { - fetch_operand(); pc = address; } - else - { - pc = pc + 1; - } } void bvs() { // branch on overflow set + fetch_operand(); if(V_IS_SET) { - fetch_operand(); pc = address; } - else - { - pc = pc + 1; - } } void clc() @@ -435,8 +406,10 @@ void jpa() void jsr() { // jump to new location saving return address - push_word(pc); address = read_word(pc); + pc = pc + 2; + + push_word(pc); pc = address; }