Raspberry Pi Basic

Does anyone know of a forum discussing Raspberry Pi RISC OS ARM BBC BASIC VI?

Particularly how to access USB ports and whether OSBYTE and OSWORD calls are implemented.

Does anyone know of a forum discussing Raspberry Pi RISC OS ARM BBC BASIC VI?

Could start here? :-)

Particularly how to access USB ports

Complicated. USB ports are accessed through the “DeviceFS” interface, so at the very least you will need to enumerate the connected USB devices to determine which device is the one you want and then look for the appropriate endpoints. Don’t forget to free all of those memory blocks as you go…

These endpoints, when found, can be opened as file handles using something like:
in% = OPENIN "Devices#interface0;endpoint1;bulk;nopad;noblock:USB10" where the endpoint number and USB device number are changed to suit.
From there, you can BGET from the in endpoint and BPUT to the out endpoint, or OS_GBPB accordingly for larger blocks.

and whether OSBYTE and OSWORD calls are implemented.

SYS “OS_Byte” and SYS “OS_Word”, perhaps? ;-)

If you are coming from a Beeb background, then:

OS_Word
A (function code) goes in R0 and XY (block pointer) goes in R1.
Replace call to &FFF1 with SYS "OS_Word", R0, R1.
Data is usually returned by updating the block passed. Refer to documentation on each call for specifics.

OS_Byte
A (function code) goes in R0. X (param one) goes in R1. Y (param two) goes in R2.
Replace call to &FFF4 with SYS "OS_Byte", R0, R1, R2 TO a%, x%, y%.
Data is usually returned in registers, here assigned as a%, x% and y%. There is also a method of using an AND…EOR mask to read/write data for the higher OS_Byte calls. Refer to the documentation on each call for specifics.

Example

Is the user holding down a Ctrl key?

Here is the BBC Micro version (which will actually work on RISC OS, though it is not recommended these days!):

10 REPEAT
20   A% = 121
30   X% = 1 EOR &80
40   Y% = 0
50   result% = USR(&FFF4)
60   IF (((result% DIV 256) AND 255) <> 0) THEN PRINT "Yes!" ELSE PRINT "No!"
70 UNTIL 0

Here is the RISC OS version:

10 REPEAT
20   SYS "OS_Byte", 121, (1 EOR &80) TO ,key%
30   IF (key% <> 0) THEN PRINT "Yes!" ELSE PRINT "No!"
40 UNTIL 0