Saver

This program reads a tape header block using a machine code routine loaded at address 32768 and displays the metadata — file type, name, length, and start address — decoded from the header bytes stored at addresses 33280–33294. It reconstructs a ready-to-type SAVE command string, including the correct keyword (LINE, CODE, DATA, or DATA$) based on the file type byte at 33280. A lookup table at line 230 maps the eight possible header type codes (0–3 covering BASIC, numeric array, string array, and code) to their display names and BASIC SAVE keywords. The program also handles the special case of a SCREEN$ file by detecting address 16384 and length 6912. Users can optionally send the SAVE command to a printer via LPRINT, reload another header, or re-save the utility itself.

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Program Analysis

Program Structure

The program divides into four logical phases:

1. Initialization (lines 10–30): Loads the companion machine code block “Saver code” to address 32768, then zeros two bytes at 33293–33294.
2. Header capture (lines 40–70): Prompts the user to play a tape, calls the machine code at USR 32768 to read a tape header, then beeps to indicate completion.
3. Data decoding (lines 80–170): Parses the raw header bytes from 33280–33294, looks up the file type, trims the filename, and reconstructs the SAVE command string.
4. Output and menu (lines 180–240): Displays options to print via LPRINT, load another header, or re-save the utility; line 240 performs the re-save.

Header Memory Map

The machine code routine deposits the decoded header fields into a fixed block of RAM starting at 33280. The layout used by the BASIC decoding code is:

Address	Content	Length
33280	File type byte (0–3)	1
33281–33290	Filename (10 chars, space-padded)	10
33291–33292	Parameter 1 (length / LINE number)	2
33293–33294	Parameter 2 (start address / array letter)	2

This layout mirrors the standard Spectrum tape header block structure, offset by 33280 from address 0. Parameter 1 (L) is computed as (PEEK 33292)*256+PEEK 33291 (little-endian) and Parameter 2 (S) similarly from 33293–33294.

File Type Lookup Table

Line 230 holds a DATA statement with four pairs of strings: a display name and a SAVE keyword fragment for each of the four header types (0 = BASIC, 1 = numeric array, 2 = string array, 3 = machine code). Line 80 reads through Q iterations (0 to T, where T is the type byte) to land on the correct pair, storing them in T$ and D$.

Filename Trimming

Lines 100–110 scan the 10-character filename string n$ from right to left, stopping at the last non-space character. The resulting index c is then used as a TO-slice bound — N$( TO c) — throughout the output lines, neatly stripping trailing spaces without any string manipulation function.

SAVE Command Reconstruction

Lines 120–150 build the extra parameter string E$ depending on file type. For BASIC (type 0), s$ is set to " (Line #)" and E$ to the autostart line number. For code (type 3), E$ becomes start,length. The special case at line 150 detects a SCREEN$ save (start 16384, length 6912) and substitutes the keyword SCREEN$, clearing D$ so the output reads SAVE "name" SCREEN$ correctly.

Machine Code Component

The 472-byte machine code block is loaded at address 32768 (just below the BASIC program area set by CLEAR 32000) and called via RANDOMIZE USR 32768 at line 60. The routine is responsible for the low-level tape reading that the Spectrum ROM’s own LOAD mechanism would ordinarily handle; using machine code allows the header bytes to be deposited into a known RAM location without affecting the BASIC program. The CLEAR 32000 at line 10 ensures the machine code area is protected from BASIC memory management.

User Interface Loop

Lines 180–220 implement a simple three-option menu using PAUSE 0 followed by INKEY$ checks. This is a standard keypress-detection idiom: PAUSE 0 waits until any key is pressed, then the subsequent IF INKEY$= tests read the still-held key. If none of the three keys match, line 220 loops back to line 190 to re-test.

Notable Anomalies

• Line 30 pre-zeros 33293–33294, which correspond to the start-address parameter for code files. This prevents a stale value being displayed if the machine code routine does not overwrite them (e.g., for BASIC file headers where this field is unused).
• The variable s (lowercase) at line 150 refers to the same value as S computed at line 130; Spectrum BASIC is case-insensitive for variable names of length > 1, but single-letter variables are case-sensitive — however S and s are the same single-letter variable in Spectrum BASIC (keywords are tokenized; variable names are stored in lowercase internally). This works correctly.
• The DATA at line 230 contains only four type entries (types 0–3), which matches the complete set of valid Spectrum header types, so no out-of-range read can occur under normal tape operation.