Z80 and Amstrad CPC programming.https://djnz.iiivan.org/enhttps://djnz.iiivan.org/en/dots-tunnel-5-ecran-256/https://djnz.iiivan.org/en/dots-tunnel-5-ecran-256/What if the CPC screen changed shape so that the address of a dot were quicker to compute? The dots tunnel moves to a square screen, then spends the time saved on more dots.Sat, 31 Oct 2026 00:00:00 GMTdemo effectsdots tunnelCPCZ80https://djnz.iiivan.org/en/dots-tunnel-4-pile-registres/https://djnz.iiivan.org/en/dots-tunnel-4-pile-registres/Where do the NOPs of a dots tunnel dot go, instruction by instruction, and how many can the Z80 stack, its registers and unrolling remove without changing a single picture?Fri, 30 Oct 2026 00:00:00 GMTdemo effectsdots tunnelCPCZ80https://djnz.iiivan.org/en/dots-tunnel-3-effacement/https://djnz.iiivan.org/en/dots-tunnel-3-effacement/The v1 of the dots tunnel clears 16 KB per picture for 256 lit bytes at most, and its picture flickers. Two versions in Z80 fix the flicker, then the clearing, and we measure what each one brings.Thu, 29 Oct 2026 00:00:00 GMTdemo effectsdots tunnelCPCZ80https://djnz.iiivan.org/en/dots-tunnel-2-cpc/https://djnz.iiivan.org/en/dots-tunnel-2-cpc/How the CPC stores its pixels in memory, the dots tunnel tables computed in Locomotive BASIC then by RASM, byte for byte, and a first, slow version of the tunnel in Z80, whose time we measure picture by picture.Wed, 28 Oct 2026 00:00:00 GMTdemo effectsdots tunnelCPCZ80https://djnz.iiivan.org/en/dots-tunnel-1-principe/https://djnz.iiivan.org/en/dots-tunnel-1-principe/Building a dots tunnel one idea at a time, in JavaScript, on a simulated CPC screen: from the projection of a circle to the byte tables the Z80 expects.Mon, 26 Oct 2026 00:00:00 GMTdemo effectsdots tunnelCPCZ80https://djnz.iiivan.org/en/tdd-cpc-string-sort/https://djnz.iiivan.org/en/tdd-cpc-string-sort/An insertion sort in Z80 on the Amstrad CPC, one test at a time, with z80-tdd: the pointers move, the strings stay where they are, strcmp compares, stability shows at last, and the budget depends on n and on the prefixes.Sun, 25 Oct 2026 12:00:00 GMTZ80CPCTDDsortinghttps://djnz.iiivan.org/en/tdd-cpc-strcmp/https://djnz.iiivan.org/en/tdd-cpc-strcmp/A string comparison in Z80 on the Amstrad CPC, one test at a time, with z80-tdd: strings in the firmware format, an answer in the flags like CP, the bit 7 trap, then a budget for each path.Sat, 24 Oct 2026 23:30:00 GMTZ80CPCTDDsortinghttps://djnz.iiivan.org/en/tdd-cpc-radix-sort/https://djnz.iiivan.org/en/tdd-cpc-radix-sort/Radix sort in Z80 on the Amstrad CPC, one test at a time, with z80-tdd: a stable counting sort that moves the keys, two passes made into one routine by a byte swap, then its budget in NOPs.Sat, 24 Oct 2026 23:00:00 GMTZ80CPCTDDsortinghttps://djnz.iiivan.org/en/tdd-cpc-counting-sort/https://djnz.iiivan.org/en/tdd-cpc-counting-sort/Counting sort in Z80 on the Amstrad CPC, one test at a time, with z80-tdd: a table of 256 counts, a scan that started in the wrong place, a table left clean, then the four sorts head to head.Sat, 24 Oct 2026 22:00:00 GMTZ80CPCTDDsortinghttps://djnz.iiivan.org/en/tdd-cpc-bubble-sort/https://djnz.iiivan.org/en/tdd-cpc-bubble-sort/Bubble sort in Z80 on the Amstrad CPC, one test at a time, with z80-tdd: a budget test decides between the classic flag and Knuth's bound, then a match of the three sorts.Sat, 24 Oct 2026 20:00:00 GMTZ80CPCTDDsortinghttps://djnz.iiivan.org/en/tdd-cpc-insertion-sort/https://djnz.iiivan.org/en/tdd-cpc-insertion-sort/Insertion sort in Z80 on the Amstrad CPC, one test at a time, with z80-tdd: four ways to shift the bytes, measured to the NOP, then a match against selection sort.Sat, 24 Oct 2026 18:00:00 GMTZ80CPCTDDsortinghttps://djnz.iiivan.org/en/tdd-cpc-selection-sort/https://djnz.iiivan.org/en/tdd-cpc-selection-sort/Sorting an array in Z80 on the Amstrad CPC, one test at a time, with z80-tdd: from O(n²) complexity to an exact formula in NOPs.Sat, 24 Oct 2026 12:00:00 GMTZ80CPCTDDsortinghttps://djnz.iiivan.org/en/tdd-cpc-find-min/https://djnz.iiivan.org/en/tdd-cpc-find-min/Writing the tests of a Z80 routine before the routine, on the Amstrad CPC: set the registers and the memory, call the routine, check the result, up to a NOP budget.Sat, 24 Oct 2026 00:00:00 GMTZ80CPCTDD