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fix: build_rdm_frame checksum off-by-one (summed 1 extra byte incl. stale template checksum)

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Default mode RDM discovery got 0 responses because the template-based builder's
checksum range was 0x3C..0x3C+msgLen (includes the old checksum slot) instead of
0x3C..0x53+PDL. build_rdm_frame2 was already correct (used by show mode).
This commit is contained in:
OpenCode 2026-09-11 17:11:27 +08:00
parent 2fb74a2f67
commit 249cd05906
1 changed files with 3 additions and 2 deletions
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5
src/hostdemo.rs
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@ -93,9 +93,10 @@ fn build_rdm_frame(dest: &[u8; 6], tn: u8, qseq: u16, cc: u8, pid: u16, pd: &[u8
f[0x51] = (pid & 0xFF) as u8;
f[0x52] = pd.len() as u8;
f[0x53..0x53 + pd.len()].copy_from_slice(pd);
// checksum: 含隐式 0xCC 起始字节, 从 CC 起 msgLen 字节 (不含自身), BE
// checksum: 含隐式 0xCC 起始字节, Σ(0x3C..0x53+PDL) (不含 checksum 槽位自身!), BE
// ★历史 bug: 曾写成 0x3C..0x3C+msg_len 多算 1 字节(含模板残留旧 checksum) → Butler 不应答
let mut sum: u16 = 0xCC;
for i in 0x3C..0x3C + msg_len { sum = sum.wrapping_add(f[i] as u16); }
for i in 0x3C..0x53 + pd.len() { sum = sum.wrapping_add(f[i] as u16); }
let cs = 0x53 + pd.len();
f[cs] = (sum >> 8) as u8;
f[cs + 1] = (sum & 0xFF) as u8;