From 07997022adf436436ca72079eb13c801e5b74c82 Mon Sep 17 00:00:00 2001
From: SDD <sdd@local>
Date: Fri, 16 Oct 2026 10:30:52 +0300
Subject: [PATCH] docs: the video RAM test draws characters then verifies;
 mapping alone cannot satisfy it

---
 harness/mame/BRINGUP_LOG.md | 32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/harness/mame/BRINGUP_LOG.md b/harness/mame/BRINGUP_LOG.md
index 071445c..dc22ed0 100644
--- a/harness/mame/BRINGUP_LOG.md
+++ b/harness/mame/BRINGUP_LOG.md
@@ -798,11 +798,35 @@ step. The bank walk observed so far steps in `0x400000` units (`>>4`), reaching
 **Honest status:** level 1 is NOT passing. Video memory is located and mapped correctly; the
 test's *requirement* is not yet understood.
 
+## The video test DRAWS, then verifies (2026-10-16)
+
+Reading the helper the test calls per bank — bit `0x3FDDFCB0`, file `0x17BF96` — shows it is
+**not** the check. It is the display:
+
+```
+3fddfd60: ... loop building 8 hex digits from a9 ...     ; format a9 as hex
+3fddff40: movk 7,a11                                      ; 8 characters
+3fddff50: movb *a5,a8 ; push char ; push a10 ; push 0xffff
+3fde0000: calla 0x3fdf97f0                                ; plot the character at a10
+3fde0030: addk 12,a10                                     ; next cell, +12
+```
+
+It formats the address in hex and **draws it on the screen**, 12 units per character, via the
+character plotter at `0x3fdf97f0`. That also explains the read PCs the catch-all saw inside
+the video region (`3FDF97A0`, `3FDF9A00` — the drawing code reading VRAM).
+
+**Consequence for the diagnosis:** the level-1 "video RAM test" **draws characters and then
+verifies them**; it is not a raw memory walk. So the fact that mapping the memory does not
+make it pass is *expected* — the check is on the drawing path, which depends on the character
+generator, not merely on memory existing.
+
+**Next:** find the verification — where the test compares what it drew against what it reads
+back. That comparison is what fails and reports error 22 at bit `0x040000C0`.
+
 ---
 
 ## Next steps
 
-1. Read the check helper at bit 0x3FDDFCB0 (file 0x17BF96) to learn what the
-   level-1 video RAM test actually requires.
-2. Map video memory at the full extent the bank walk reaches.
-3. Re-run the console check after each change.
+1. Find the VERIFY step of the video RAM test (what it compares after drawing).
+2. That comparison is what fails; it likely needs the character generator / font data.
+3. Re-run the console check (cap.lua) after each change.