LBYTES

Syntax

LBYTES device_filename, start or

LBYTES [device_]filename, start(Toolkit II only) or

LBYTES #channel, start(SMS only)

Location QL ROM, Toolkit II

This command loads a chunk of machine code (or data) stored on the given device under the specified filename and will report the error ‘Not Found’ (-7) if either the device or filename does not exist. If Toolkit II is present, this command supports the default data device (see DATAD$). If found, the chunk of machine code is loaded into the QL, starting at the specified start address. The code is loaded in one huge block, which means that loading is very quick. However, there is also no check on the type of file being loaded and therefore you should make sure that you know what you are doing. Under SMS the third variant allows you to load the data from the specified channel which must be open to a file. This allows for more efficient programs, so that you can perform various tests on the file beforehand (such as test its length and file type), whilst only opening a channel to the file once.

Examples

One of the main uses of this command is to load in machine code Toolkits and extensions. It is important to note that if this command is used to do this, on pre JS ROMs, the commands in the machine code Toolkit cannot be used in the same program which links them in. A typical boot program would therefore be:

100 a=RESPR (1024) : LBYTES flp1_Toolkit_ext,a : CALL a
110 LRUN flp1_Main_bas

Another use of LBYTES may be to load a screen which has been designed in a drawing program. A normal QL screen is a maximum of 32768 bytes long, however quite often screens can be much larger, so it is important to ensure that you check the length of the file before loading in what may be a screen file. To load a screen under SMS, use:

10 OPEN_IN #3,flp1_Loading_scr
20 scr_length=FLEN (#3)
30 scr_size=SCR_YLIM * SCR_LLEN
40 IF scr_size < scr_length
42 PRINT #0,'Screen resolution is too small for the saved file.':STOP
45 END IF
50 IF scr_size>scr_length:PRINT #0,'Screen resolution is too big for the saved file.':STOP
60 LBYTES #3,SCR_BASE
70 CLOSE #3

WARNING

There is no check on the value of start, so ensure that you only try to LBYTES machine code into RAM which has been set aside with ALCHP or RESPR. Also ensure that the file is not too long to fit in the area of RAM allocated.

CROSS-REFERENCE

Normally code loaded with LBYTES has been saved using SEXEC or SBYTES. FLEN allows you to find out the length of a file, FTYP its file type.