René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Error in M68000 test code : ignore it ... mem assumption is false (you can delete it)","articleBody":"in the exerciser code we can see:\n`00000DA2                           881              * EA = x.L  - BYTE only\n\n00000DA2  207C 000F0100            882              move.l #$000F0100 , a0      * point to memory to address 0x100 \n\n00000DA8  10FC 0001                883              move.b #$01 , (a0)+         * populate test data\n\n00000DAC  10FC 00FC                884              move.b #$FC , (a0)+         * populate test data\n\n00000DB0  10FC 0080                885              move.b #$80 , (a0)+         * populate test data\n\n00000DB4  0879 0000 000F0100       886              bchg.b #0 , $000F0100 \n\n00000DBC  6700 0248                887              beq BCHG_FAIL               * branch if Z set\n\n00000DC0  0879 0001 000F0101       888              bchg.b #1 , $000F0101       * \n\n00000DC8  6600 023C                889              bne BCHG_FAIL               * branch if Z clear  \n\n00000DCC  0879 0007 000F0102       890              bchg.b #7 , $000F0102       * \n\n00000DD4  6700 0230                891              beq BCHG_FAIL               * branch if Z set\n\n00000DD8  207C 00000100            892              move.l #$00000100 , a0      * point to memory to address 0x100 \n\n00000DDE  0C18 0001                893              cmpi.b #$01 , (a0)+\n\n00000DE2  6600 0222                894              bne BCHG_FAIL               * branch if Z clear  \n\n00000DE6  0C18 00FC                895              cmpi.b #$FC , (a0)+\n\n00000DEA  6600 021A                896              bne BCHG_FAIL               * branch if Z clear  \n\n00000DEE  0C18 0080                897              cmpi.b #$80 , (a0)+\n\n00000DF2  6600 0212                898              bne BCHG_FAIL               * branch if Z clear  \n`\nat line 883, mem is set at 0x01, at line 886, bit 0 is changed, so mem is now 0x00. At line 893 we test against 0x01 erroneously ...\n\nI made the assumption that mem is only 16 bits addresses ...\n\nWe also see:\n`000010DE                          1146              * EA = n(An,D.W)  - BYTE only\n\n000010DE  207C 00000100           1147              move.l #$00000100 , a0      * point to memory to address\n\n000010E4  227C 00000000           1148              move.l #$00000000 , a1      * point to memory to address\n\n000010EA  247C 00000001           1149              move.l #$00000001 , a2      * point to memory to address\n\n000010F0  7000                    1150              move.l #$00000000 , d0      * point to memory to address\n\n000010F2  7201                    1151              move.l #$00000001 , d1      * point to memory to address\n\n000010F4  10FC 00FF               1152              move.b #$FF , (a0)+         * populate test data\n\n000010F8  10FC 00FF               1153              move.b #$FF , (a0)+         * populate test data\n\n000010FC  207C 00000100           1154              move.l #$00000100 , a0      * point to memory to address\n\n00001102  08B0 0000 0000          1155              bclr.b #0 , 0(a0,d0.w)            \n\n00001108  67FE                    1156              beq *               * branch if Z set\n\n0000110A  08B0 0001 1000          1157              bclr.b #1 , 0(a0,d1.w)      * \n\n00001110  67FE                    1158              beq *               * branch if Z set\n\n00001112  08B0 0002 1001          1159              bclr.b #2 , 1(a0,d1.w)      * \n\n00001118  66FE                    1160              bne *               * branch if Z clear  `\n\nmem is only initialised for addresses 0x100 \u0026 0x101 at lines 1147 to 1153. And at line 1159 the memtested is  at address 0x102 ???\n","author":{"url":"https://github.com/OulanB","@type":"Person","name":"OulanB"},"datePublished":"2025-10-17T11:40:06.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/45/Projects/issues/45"}