84 lines
2.9 KiB
Markdown
84 lines
2.9 KiB
Markdown
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# Making an ATmega328P blink
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Collapse OS has an AVR assembler and an AVR programmer. If you
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have a SPI relay as described in the SD card recipe, then you
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almost have all it takes to make an ATmega328P blink.
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First, read `doc/avr.txt`. You'll see that it tells you how to
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build an AVR programmer that works with your SPI relay. You
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might already have such device. For example, I use the same
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device as the one I connect to my Sparkfun AVR Pocket
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Programmer, but I've added an on/off switch to it. I then use
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a 6-pin ribbon cable to connect it to my SPI relay.
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If you have a SD card connected to the same SPI relay, you'll
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face a timing challenge: SD specs specifies that the minimum
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SPI clock is 100kHz, but depending on your setup, you might end
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up with an effective `SCK` below that. My own clock setup looks
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like this:
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I have a RC2014 Dual clock which allows me to have easy access
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to many clock speeds, but the slowest option is 300kHz, not
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slow enough. My SPI relay has a pin for input clock override,
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and I built a pluggable 4040 with a switch that selects a
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divisor. I plug that module in my SPI relay, then I plug that
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into my RC2014 Dual clock. When doing SD card stuff, I select
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the "no division" position, and when I communicate with the
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AVR chip, I move the switch to increase the divisor.
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Once you've done this, you can test that you can communicate
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with your AVR chip by doing `160 162 LOADR` (turn off your
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programmer or alse it might mess up the SPI bus and prevent you
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from using your SD card) and then running:
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1 asp$ aspfl@ .x 0 (spie)
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(Replace `1` by your SPI device ID) If everything works fine,
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you'll get the value of the low fuse of the chip.
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## Building the blink binary
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A blink program for the ATmega328P in Collapse OS would look
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like this:
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50 LOAD ( avra ) 65 66 LOADR ( atmega328p ) H@ ORG !
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DDRB 5 SBI, PORTB 5 CBI,
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R16 TCCR0B IN, R16 0x05 ORI, TCCR0B R16 OUT,
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R1 CLR,
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L1 LBL! ( loop )
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R16 TIFR0 IN,
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R16 0 ( TOV0 ) SBRS,
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L1 ( loop ) ' RJMP LBL, ( no overflow )
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R16 0x01 LDI, TIFR0 R16 OUT,
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R1 INC,
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PORTB 5 CBI,
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R1 7 SBRS,
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PORTB 5 SBI,
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L1 ( loop ) ' RJMP LBL,
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See `doc/asm.txt` for details. For now, you'll paste this into
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an arbitrary unused block. Let's use `999`.
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$ cd recipes/rc2014
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$ xsel > blk/999
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$ rm blkfs
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$ make
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$ dd if=blkfs of=/dev/<your-sdcard> bs=1024
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Now, with your updated SD card in your RC2014, let's assemble
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this binary:
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999 LOAD
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H@ CREATE end ,
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CREATE wordcnt end ORG @ - 2 / ,
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: write 1 asp$ asperase wordcnt 0 DO
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ORG @ I 2 * + @ I aspfb! LOOP
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0 aspfp! 0 (spie) ;
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write
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The first line assembles a 16 words binary beginning at `ORG @`,
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then the rest of the lines are about writing these 16 words to
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the AVR chip (see `doc/avr.txt` for details). After you've run
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this, if everything went well, that chip if it has a LED
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attached to PB5, will make that LED blink slowly.
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