Changes from NFS 3.60 to NFS 3.62
NFS 3.62 is a minimal bug-fix release of Acorn NFS 3.60 for the BBC Micro.
The two 8 KB ROMs are 99.7% identical at the opcode level, with only 16 bytes
differing. The single functional change fixes a command-matching bug where
*EXEC was incorrectly caught by the *EX entry in the command table.
Summary statistics
| Metric | Value |
|---|---|
| ROM size | 8192 bytes |
| Identical bytes at same offset | 8176 (99.8%) |
| Byte-level similarity | 99.8% |
| Opcode-level similarity | 99.7% |
| Full instruction similarity | 99.7% |
| Instructions (3.60 / 3.62) | 4073 / 4067 |
| Structural change blocks | 4 |
ROM header
| Field | 3.60 | 3.62 |
|---|---|---|
| Title | " NET" | " NET" |
| ROM type | &82 | &82 |
| Binary version | &83 | &83 |
| Copyright | "(C)ROFF" | "(C)ROFF" |
| Language entry | &80E1 | &80E1 |
| Service entry | &80F7 | &80F7 |
All header fields are functionally unchanged. The language and service entry points remain at &80E1 and &80F7.
Changes
1. Version identification
The ROM header version byte at &8023 changes from &60 to &62, and the version
string at &820B changes from "NFS 3.60" to "NFS 3.62".
2. EX vs EXEC disambiguation (bug fix)
In NFS 3.60, the *EX entry in the FS command match table at &8C4B dispatches
directly to ex_handler at &8C61. This means any command beginning with "EX"
— including *EXEC — is matched as *EX and handled locally as a directory
listing rather than being forwarded to the fileserver.
NFS 3.62 fixes this by changing the *EX dispatch address in the command table
from &8C61 to &9FB5, where a new 12-byte trampoline routine checks whether the
command continues past "EX":
| Address | Instruction | Purpose |
|---|---|---|
| &9FB5 | LDA (fs_crc_lo),Y |
Load next character from command |
| &9FB7 | CMP #&21 |
Printable non-space character? |
| &9FB9 | BCS [&9FBE](3.62.html#addr-9FBE) |
Yes: command continues, forward to FS |
| &9FBB | JMP ex_handler |
No: terminated, handle *EX locally |
| &9FBE | JMP forward_star_cmd |
Forward *EXEC etc. to fileserver |
If the character after "EX" is below &21 (space, CR, or control character),
the command is *EX and control passes to ex_handler at &8C61 as before.
If the character is &21 or above (a printable character), the command is
something like *EXEC and is forwarded to the fileserver via
forward_star_cmd at &80C1.
The trampoline occupies 12 bytes of the &FF padding at the end of the ROM (&9FB5-&9FC0), reducing the unused space from 75 bytes to 63 bytes.
The two byte changes in the command table data are:
| Address | 3.60 | 3.62 | Meaning |
|---|---|---|---|
| &8C57 | &8C | &9F | Dispatch address high byte |
| &8C58 | &60 | &B4 | Dispatch address low byte |
These encode the PHA/PHA/RTS dispatch target as (address-1): &8C60 → &8C61 in 3.60, &9FB4 → &9FB5 in 3.62.
Relocated code blocks
All four relocated code blocks are byte-identical between 3.60 and 3.62, at the same ROM source addresses:
| Block | ROM source | Runtime dest | Length |
|---|---|---|---|
| Workspace | &9321 | &0016 | &61 |
| Page 4 | &9362 | &0400 | &100 |
| Page 5 | &9462 | &0500 | &100 |
| Page 6 | &9562 | &0600 | &100 |