BBC BASIC - Changing Colours In Assembler Code

Another thing I’d love to see added is ADRL.

+1 and LDRL

Now, assembly language makes the BASIC program executions substantially faster but it may prove temperamental. If one doesn’t know what one is doing, you could be slapped in the face by RISC OS in the BASIC interpreter with “Bad immediate constant” messages for no reason. When that happens, it is nearly impossible to track the bug down that leads to that.

But when you deal with VDU calls for graphic text character size adjustments, to implement, for instance, this BASIC code:

VDU 23,17,7,6,8;8;0;0

Do you use an OS command in a sequence in an assembly code such as OS_Write or OS_Byte?

you could be slapped in the face by RISC OS in the BASIC interpreter with “Bad immediate constant” messages for no reason.

The reason is exactly as stated. While you can store any 32 bit value in a register, instructions such as MOV and ADD have a limited range of valid values, due to having to fit the value into the instruction. Assume it is approximately an 8 bit value which may be shifted. So 255 is valid but 1356347 is not.
If you want to be able to set any value, store it to a word in memory and then LDR that word into a register.

But when you deal with VDU calls for graphic text character size adjustments, to implement, for instance, this BASIC code:
VDU 23,17,7,6,8;8;0;0
Do you use an OS command in a sequence in an assembly code such as OS_Write or OS_Byte?

You have already asked this and it has been answered. OS_WriteC to write byte by byte, or OS_WriteN to do it as a block all at once.
Pay attention to the semicolons, that’s shorthand for sending 16 bit values, so you’ll need to send the low byte first followed by the high byte (or a null if the value is less than 256).
In your example, that ought to become 23,17,7,6,8,0,8,0,0,0,0

@Angel: Regarding “When that happens, it is nearly impossible to track the bug down that leads to that” I assume you don’t have a line like

ON ERROR REPORT: PRINT"Error at line ";ERL: A$=GET$: END

I assume you don’t have a line like

ON ERROR REPORT: PRINT"Error at line ";ERL: A$=GET$: END

at the beginning of your BASIC code ?

Better still is to use throwback. Either Joe Taylor’s !Throwback or Reporter with the *ReportError Throwback command.