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pureboot: W addresses a page, not a word in it

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The in-page bits of a W address are dropped so the fill always walks from
the page base; the wire contract is one page of data for any address
inside it, on both the byte- and the word-addressed path. +2 B.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
BlackMark
2026-07-22 23:43:41 +02:00
parent a5b42bc02f
commit c763ca856a
3 changed files with 23 additions and 10 deletions
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6
pureboot/README.md
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@@ -127,15 +127,15 @@ addresses and all counts are bytes.
|---|---|---|
| `b` | — | the 12-byte info block |
| `R` | addr16, n8 | n flash bytes (n = 0 means 256) |
| `W` | addr16, then one page of data | — (completion = next prompt) |
| `W` | addr16 (any address in the page), then one page of data | — (completion = next prompt) |
| `r` | addr16, n8 | n EEPROM bytes (n = 0 means 256) |
| `w` | addr16, n8, then n data bytes | `+` per byte, sent once its write has begun |
| `F` | — | 4 bytes: low fuse, lock, extended fuse, high fuse |
| `J` | word address (16-bit) | `+`, then execution continues there |
| other | — | ignored; the loop re-prompts (send a junk byte, await `+`, to resync) |
`W` streams exactly one page-aligned SPM page (size from the info block) into
the buffer, then erases and programs — except pages inside the 512-byte slot
`W` streams exactly one SPM page (size from the info block) into the buffer,
then erases and programs — except pages inside the 512-byte slot
the loader is *running* in, which are drained and left alone, so a broken host
cannot brick the running copy and a staged copy may rewrite the resident.