C64-dev/newLang/planning/claims/E01-S04.md

---

story: E01-S04 owner: e01_display_clock status: done started: 2026-11-07 depends-on: [E01-S01]

E01-S04 Claim

Intended change

Create a separate C128 platform probe that demonstrates KERNAL-compatible text on the 40- and 80-column displays, observes safe 1/2 MHz selection behavior, and documents a deterministic compiler fallback without using VDC RAM for semantic state.

File area

• src/platform/display-clock.s
• cfg/display-clock-c128.cfg
• scripts/build-display-clock.ps1
• scripts/verify-display-clock.ps1
• monitor/display-clock-*.txt
• docs/platform-display-clock.md
• generated evidence under build/

Acceptance evidence

• Text is legible in tested 40- and 80-column modes.
• Safe clock switching conditions are documented from observed behavior.
• No semantic compiler data is placed in VDC RAM.
• Fallback clock/display behavior is deterministic.

Coordination notes

E01-S02 owns MMU/common-RAM probes in separate files. This story does not freeze the final compiler memory map or alter E01-S01.

Work log

• Read scoped instructions, canonical documents, and compiler/VICE skills.
• Used the primary C128 guide's $D7, $D030, and KERNAL facts to define the probe policy.
• Added an independent PRG, linker layout, clean build, remote-monitor verification, non-stopping trace commands, and two display captures.
• Verified the 40-column path never enters the fast checkpoint.
• Verified the 80-column path observes $D030 bit 0 set while KERNAL text is emitted, then clears it before return.
• Statically rejected executable $D600/$D601 references and kept semantic markers in ordinary CPU RAM at $1D13/$1D14.
• Visually inspected both generated screenshots; expected messages are legible and both sessions return to READY..

Completion

• Tests run: scripts/build-display-clock.ps1; scripts/verify-display-clock.ps1; tests/grammar/validate.ps1; scripts/build-minimal.ps1
• Results: 278-byte probe builds; x128 40-column result $44 and 80-column result $85; both preserve $5A/$C3 semantic markers and leave speed bit 0 clear; trace paths and screenshots match the documented modes; grammar and minimal-PRG regressions pass
• Files changed: separate E01-S04 source/config/scripts/trace/documentation, the display/clock architecture paragraph, and this claim
• Remaining risks: VICE is mandatory evidence, but physical C128 validation is still the P2 E08-S06 story; final compiler addresses remain E01-S05 work