Booting Beagleboard by BBC BASIC
Below is a very short BBC BASIC program that assembles some code and uploads it to the BB internal memory. You have to hold down the USR button on powerup/reset to get it to talk. (The slowest part in development was noticing out that the initial boot sequence uses 8E1 protocol, and not the 8N1 that the x-loader and u-boot and linux do.)
I wanted to get into the boot process as early as possible without continuously re-flashing the NAND ROM, and also avoiding plugging an SD card into the somewhat worn out socket.
Brunel OS is an idea I've been thinking about for years, with a concept based on an Eiffel inspired language that handles multi-threading by simply only alowing one thread at a time access to any object and allowing threads to pass through multiple memory maps (somewhat different to the process model of other operating systems I've had experience of).
So, an example of loading a very small program into internal RAM of the BeagleBoard from a Risc PC:
SYS"OS_SerialOp", 0, &106, &fffffe00 SYS"OS_SerialOp", 1, %011000 SYS"OS_SerialOp", 5, 18 SYS"OS_SerialOp", 6, 18 PROCassemble REM Receive ASIC ID (and ignore it, for the time being) FOR R%=1 TO 58 REPEAT SYS"OS_SerialOp", 4 TO ,J%;F% UNTIL (F% AND 2) = 0 PRINT RIGHT$( "0"+STR$~J%, 2 ); NEXT PRINT "Sending boot command" PROCput( 2 ) PROCput( 0 ) PROCput( 3 ) PROCput( &f0 ) PRINT "Boot command sent" DIM B% 4 !B%=P%-code% PROCput( B%?0 ) PROCput( B%?1 ) PROCput( B%?2 ) PROCput( B%?3 ) PRINT "Length sent ";!B% T%=0 FOR Q%=code% TO P% SYS"OS_SerialOp", 4 TO ,J%;F% IF (F% AND 2) = 0 THEN PROCshow( J% ) ENDIF PROCput( ?Q% ) T%+=1 NEXT PRINT "Transmission finished "; T%; " bytes" REM Kind of terminal (one way, at the moment) REPEAT REPEAT SYS"OS_SerialOp", 4 TO ,J%;F% UNTIL (F% AND 2) = 0 PROCshow( J% ) UNTIL 0 END DEF PROCput( C% ) REPEAT SYS"OS_SerialOp", 3, C% TO ; F% UNTIL (F% AND 2) = 0 ENDPROC DEF PROCshow( C% ) R%+=1 IF C%>31 OR C%=10 OR C%=13 THEN VDU C% ELSE PRINT "<";~C%;">" ENDIF ENDPROC DEF PROCassemble DIM code% 1000 FOR I%=0 TO 1 P%=code% [OPT 3*I% MOV r9, #&49000000 ORR r9, r9, #&00020000 ADR r1, welcome .write_loop LDRB r2, [r1], #1 CMP r2, #0 STRNEB r2, [r9] ;This can overflow the buffer, but it's not important yet BNE write_loop .loop B loop .welcome EQUS "Welcome to Brunel OS 0.0.0-1"+CHR$10+CHR$13 EQUB 0 ALIGN ] NEXT ENDPROC
04010501343007561302010012150100000000000000000000000000000000000000001415010000000000000000000000000000000000000000Sending boot command Boot command sent Length sent 64 Transmission finished 65 bytes Welcome to Brunel OS 0.0.0-1