-- Drive src/player/scsigate.s: can the 68000 reach the MB89352? (ROADMAP P4)
--
-- Bus errors are EXPECTED and are data: the gate probes one address at a time
-- and survives each fault, so a hole in the decode costs an entry in the map
-- rather than the rest of the run.  See src/player/scsigate.s.
--
-- THE APPARATUS, STATED UP FRONT.  This runs `x68000 -exp1 cz6bs1`, which is
-- the board FINDINGS 42.5 says to benchmark and never `x68ksupr` (whose
-- internal SCSI is PIO-only in MAME -- `// TODO: duplicate DMA glue from
-- CZ-6BS1`).  MAME refuses to instantiate the card without an 8 KB
-- `scsiexrom.bin`, which is not in this tree; the rig supplies a ZERO-FILLED
-- placeholder on a SEPARATE rompath so the user's own romset is untouched.
--
-- THAT PLACEHOLDER IS HONEST HERE AND WOULD NOT BE EVERYWHERE.  The CZ-6BS1's
-- boot ROM exists to make the card bootable through IOCS.  This player drives
-- the SPC registers directly and never executes a byte of it -- that was
-- already the plan in docs/BENCHMARK.md item 4, long before the ROM was missing
-- -- so a blank one changes nothing this rig measures.  What it WOULD change is
-- anything that booted from the card or called SCSI IOCS; do not reuse it for
-- that.  The run prints the substitution rather than burying it.
--
-- WHAT A GREEN RUN MEANS, and what it does not.  It means the 68000 reaches the
-- SPC and the register map is the one the driver will be written against.  It
-- says NOTHING about rate: MAME's device models are functional, not
-- transfer-timing accurate (docs/BENCHMARK.md), and 42.5 shows its DMAC is
-- configured in wall-clock attotimes rather than per-operand cycles.  `W` is
-- untouched by anything here.
local M  = manager.machine
local SP = M.devices[":maincpu"].spaces["program"]
local function P(s) print("[SCSI] "..s) end
local function T() local t=M.time; return t.seconds + t.attoseconds/1e18 end

local SCFLAG, SCN, SCVAL, SCOK, SCTMP, SCTMPOK =
      0x18080, 64, 0x18100, 0x18140, 0x180D0, 0x180D4
local SCRD, SCDST, SCBLKS = 0x180D8, 0x20000, 8
local SC_ERR, SC_STAT, SC_PH = 0x18200, 0x18204, 0x18208
local ERRNAME = {[0]="OK", "SELECTION TIMEOUT -- no target answered",
                 "UNEXPECTED PHASE", "POLL TIMEOUT -- a phase never arrived",
                 "NON-ZERO SCSI STATUS"}
local DISK = os.getenv("DLX_SCSI_IMG") or "dlxdisk.img"

local code do local f=io.open("scsigate.bin","rb"); code=f:read("a"); f:close() end

local st = "boot"
SUB = emu.add_machine_frame_notifier(function()
  local ok, err = pcall(function()
    if st == "boot" then
      if T() < 3.0 then return end
      for i = 1, #code do SP:write_u8(0x10000+i-1, string.byte(code,i)) end
      SP:write_u32(SCFLAG, 0)
      local cpu = M.devices[":maincpu"]
      cpu.state["SR"].value = 0x2700
      cpu.state["SP"].value = 0x8000
      cpu.state["PC"].value = 0x10000
      P(string.format("scsigate.bin=%d B loaded at $10000", #code))
      st = "wait"; return
    end
    if st == "wait" then
      local fl = SP:read_u32(SCFLAG)
      if fl ~= 1 then
        if T() > 30 then P("TIMEOUT: the gate never finished"); P("done"); M:exit() end
        return
      end
      -- THE MAP, address by address.  A dead address is a bus error the
      -- gate survived, not a run that stopped.
      local live, dead = {}, {}
      for i = 0, SCN-1 do
        if SP:read_u8(SCOK+i) == 1 then live[#live+1] = i else dead[#dead+1] = i end
      end
      for row = 0, (SCN/16)-1 do
        local t = {}
        for i = 0, 15 do
          local a = row*16 + i
          t[#t+1] = (SP:read_u8(SCOK+a) == 1)
                    and string.format("%02X", SP:read_u8(SCVAL+a)) or "--"
        end
        P(string.format("  $EA%04X: %s", row*16, table.concat(t, " ")))
      end
      P(string.format("ANSWERED %d of %d addresses; \"--\" is a bus error.",
                      #live, SCN))
      -- The lane question, decided by which addresses answer.
      local odd_live, even_live = 0, 0
      for _, a in ipairs(live) do
        if a % 2 == 1 then odd_live = odd_live + 1 else even_live = even_live + 1 end
      end
      P(string.format("LANES: %d odd addresses answer, %d even.", odd_live, even_live))
      if SP:read_u32(SCTMPOK) == 1 then
        P(string.format("TEMP writeback ($EA0017): wrote $A5, read back $%02X",
                        SP:read_u32(SCTMP) & 0xFF))
      else
        P("TEMP writeback ($EA0017): BUS ERROR -- not a writable register here.")
      end
      P(string.format("DREG writeback ($EA0015): wrote $5A, SSTS then $%02X "
                      .."(FIFO %s), read back $%02X",
                      SP:read_u32(0x180E0) & 0xFF,
                      ((SP:read_u32(0x180E0) & 1) == 1) and "EMPTY -- the write "
                      .."never reached dreg_w" or "has a byte",
                      SP:read_u32(0x180DC) & 0xFF))
      -- The trace, whatever happened.
      local ntr = SP:read_u32(0x18230)
      if ntr > 0 then
        P("trace (SSTS PSNS INTS SERR | TCH TCM TCL | where):")
        for i = 0, ntr-1 do
          local b = {}
          for k = 0, 7 do b[k+1] = string.format("%02X", SP:read_u8(0x18240+i*8+k)) end
          local WH = {[0]="init", "selected", "INTS cleared", "phase loop saw REQ",
                      "TRANSFER issued (out)", "bytes handed over",
                      "after xfer wait", "TRANSFER issued (in)",
                      "bytes taken from FIFO", "after IN xfer wait",
                      "after bus release"}
          P(string.format("  %2d: %s %s %s %s | %s %s %s | %s", i,
            b[1], b[2], b[3], b[4], b[5], b[6], b[7],
            WH[tonumber(b[8], 16)] or b[8]))
        end
      end
      -- THE READ.  Verified against the host's copy of the same image: a
      -- transport that returns the wrong bytes without saying so is exactly the
      -- failure a checksum-free ring cannot survive (49.2).
      local rd = SP:read_u32(SCRD)
      local e  = SP:read_u32(0x180E8)
      if rd ~= 0 or e ~= 0 then
        P(string.format("scsi_read FAILED: err=%d (%s), status=$%02X, phase=%d",
                        e, ERRNAME[e] or "?", SP:read_u32(SC_STAT) & 0xFF,
                        SP:read_u32(SC_PH)))
      else
        local f = io.open(DISK, "rb")
        if not f then
          P("scsi_read returned OK but "..DISK.." is not here to check it against.")
        else
          local want = f:read(SCBLKS * 512); f:close()
          local bad, first = 0, nil
          for i = 1, #want do
            if SP:read_u8(SCDST + i - 1) ~= string.byte(want, i) then
              bad = bad + 1; first = first or (i-1)
            end
          end
          if bad == 0 then
            P(string.format("READ(10) OK: %d B from LBA 0 match %s byte for byte.",
                            #want, DISK))
          else
            P(string.format("READ(10) WRONG: %d of %d bytes differ, first at +%d.",
                            bad, #want, first))
          end
        end
      end
      -- The second read, at a non-zero LBA.
      local rd2 = SP:read_u32(0x180E4)
      if rd2 ~= 0 then
        P(string.format("second scsi_read FAILED: err=%d (%s)",
                        SP:read_u32(0x180EC),
                        ERRNAME[SP:read_u32(0x180EC)] or "?"))
      else
        local f = io.open(DISK, "rb")
        if f then
          f:seek("set", 1000 * 512)
          local want = f:read(4 * 512); f:close()
          local bad = 0
          for i = 1, #want do
            if SP:read_u8(0x28000 + i - 1) ~= string.byte(want, i) then bad = bad + 1 end
          end
          P(bad == 0
            and string.format("READ(10) OK: %d B from LBA 1000 match too.", #want)
            or  string.format("READ(10) WRONG at LBA 1000: %d of %d differ.", bad, #want))
        end
      end
      P("done"); M:exit(); return
    end
  end)
  if not ok then P("LUA ERROR: "..tostring(err)); P("done"); M:exit() end
end)