TRS-80 DOS - NEWDOS/80 v2.0 for the Model I - SYS10/SYS Disassembled

SYS10/SYS

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Description: SYS10 implements the BASIC GET and PUT statements for random access file I/O. GET reads a record from a random file into the file buffer, while PUT writes the current buffer contents to a record. This module handles record number parsing, position management, buffer synchronization, and the actual data transfer operations. It is loaded on demand when GET or PUT is executed and must be present on the system diskette.

Key Functions:

• Parse optional record numbers
• Handle modifiers: TO, #, $, %, &, !
• Calculate file positions from record numbers
• Transfer data between buffer and BASIC variables
• Support for all BASIC variable types (string, integer, single, double)

Regular Variables

Self Modifying Code

4D00H - Quick Return Entry Point

This is a quick-return entry point that cleans up the stack and returns. It's used when GET/PUT operations complete successfully without needing to process further. The two INC SP instructions discard a return address from the stack.

4D03H - Main GET/PUT Entry Point

This is the main entry point called from BASIC/CMD at 6125H (PUT) and 6126H (GET). When called, the Z flag indicates GET (Z set) or PUT (Z clear), and IX points to the FCB work area at 5700H. This routine enables position updates, retrieves the file status, sets the appropriate mode bit (bit 4 for PUT), and begins processing the record operation.

4D5AH - Parse Optional Modifiers

This section handles optional modifier characters that can appear after GET/PUT. Valid modifiers include: CFH (TO token), #, $, %, &, and !. Each modifier changes how the record operation is performed.

4DBCH - Exclamation Point Modifier Handler

This section handles the ! modifier which provides direct variable access for GET/PUT operations. It parses variable type suffixes ($, #, %) and performs type-specific data transfers between the file buffer and BASIC variables.

4E48H - Sequential File Handler

This routine handles GET/PUT operations on sequential (non-random) files. It validates the file mode and synchronizes buffer positions before performing the data transfer.

4E5FH - Numeric Record Number Parser

This routine parses a numeric record number from the BASIC statement. It evaluates the expression, validates the result is within valid record number range, and converts it to a file position for the GET/PUT operation.

4E9AH - Special Record Mode Handler (Type 09H)

This section handles files opened with special mode 09H. It performs buffer position calculation and validates the operation before proceeding with the data transfer.

4EBEH - Main GET/PUT Data Transfer

This is the main data transfer section for GET/PUT operations. It determines the file mode (sequential vs random, read vs write) and performs the appropriate data transfer between the file buffer and BASIC's data areas.

4F0EH - Buffer Boundary Check

This short routine checks if the current buffer position is at a sector boundary. It loads the buffer pointer and tests against the record length to determine if a new sector needs to be read or written.

4F18H - Standard Read/Write Mode Processing

This section handles GET/PUT for files opened with explicit read or write mode (bits 0-1 set in status). It sets up field variables, parses variable lists, and manages the data transfer between the buffer and BASIC variables.

4F8BH - Field Base Address Loader

This routine loads the field base address into DE from a self-modifying storage location. It also stores the position bounds for range checking during data transfers.

4FC1H - Statement Continuation Parser

This routine parses the BASIC statement to find continuation tokens, handling line continuation across multiple lines and checking for end of statement conditions.

4FDFH - Variable Expression Parser

This section parses variable expressions for GET/PUT variable lists. It handles different data types (string, integer, single, double) and manages data transfer between the file buffer and variable storage.

506AH - Special Type Handler (# Prefix)

This section handles variables with # prefix notation, which indicates alternate field access or special numeric formatting.

50BFH - Numeric Type Handler

This section handles numeric variable types (integer, single, double precision) for GET/PUT operations, setting up the appropriate buffer sizes and calling the data transfer routines.

50F6H - PUT Variable Handler

This section handles PUT operations for writing variable data to the file buffer. It determines the variable type, extracts the data, and writes it to the appropriate buffer position.

5144H - Special PUT Type Handler

Handles PUT operations for special variable types including # prefix notation and direct field writes.

518EH - Continue Processing / Return Handler

This section handles the completion of each variable in a GET/PUT list and determines whether to continue with more variables or finish the statement.

51CEH - Reserved/NOP Area

This area contains NOP bytes (00H) serving as padding or reserved space at the end of the SYS10 module.