For more precise timing, the SERIAL() command can be used. GPIO writes are buffered and dispatched at the end of each frame, allowing clock cycling at higher and/or more regular speeds than is possible by manually bit-banging using POKE() calls.
SERIAL(CHANNEL, ADDRESS, LENGTH)
CHANNEL:
0x000..0x0fe corresponds to gpio pin numbers; send 0x00 for LOW or 0xFF for HIGH
0x0ff delay; length is taken to mean "duration" in microseconds (excl. overhead)
0x400..0x401 ws281x LED string (experimental)
ADDRESS: The PICO-8 memory location to read from / write to.
LENGTH: Number of bytes to send. 1/8ths are allowed to send partial bit strings.
For example, to send a byte one bit at a time to a typical APA102 LED string:
VAL = 42 -- VALUE TO SEND
DAT = 16 CLK = 15 -- DATA AND CLOCK PINS DEPEND ON DEVICE
POKE(0X4300,0) -- DATA TO SEND (SINGLE BYTES: 0 OR 0XFF)
POKE(0X4301,0XFF)
FOR B=0,7 DO
-- SEND THE BIT (HIGH FIRST)
SERIAL(DAT, BAND(VAL, SHL(1,7-B))>0 AND 0X4301 OR 0X4300, 1)
-- CYCLE THE CLOCK
SERIAL(CLK, 0X4301)
SERIAL(0XFF, 5) -- DELAY 5
SERIAL(CLK, 0X4300)
SERIAL(0XFF, 5) -- DELAY 5
END
Additional channels are available for bytestreams to and from the host operating system. These are intended to be most useful for UNIX-like environments while developing toolchains, and are not available while running a BBS or exported cart [1]. Maximum transfer rate in all cases is 64k/sec (blocks cpu).
0x800 dropped file // stat(120) returns TRUE when data is available
0x802 dropped image // stat(121) returns TRUE when data is available
0x804 stdin
0x805 stdout
0x806 file specified with: pico8 -i filename
0x807 file specified with: pico8 -o filename
0x808 [undocumented] pcm audio (see here)
Image files dropped into PICO-8 show up on channel 0x802 as a bytestream with a special format: The first 4 bytes are the image's width and height (2 bytes each little-endian, like PEEK2), followed by the image in reading order, one byte per pixel, colour-fitted to the display palette at the time the file was dropped.
[1] Channels 0x800 and 0x802 are available in the BBS and exported carts but with a maximum file size of 256k, or 128x128 for images.
