I have a situation in which a write to SPI seems to crash the Microbit. I’ve been looking at this for an hour or two now. I really cannot see what is wrong.
My Makecode extension to drive a Nokia 3310 LCD screen (84 x 48 pixels) is in this repository
The TS file has shims for lots of functions that I have transferred to the .cpp file to speed up all the graphics. I’m transferring all the SPI routines to C as well.
The extension beings by calling
init() in JS which in turn calls
SPIinit() (in the CPP) to initialise the SPI port.
init() then sets up the LCD display with several commands - these are determine by setting Digital Pin16 to low (LCD_CMD). Data writes to the screen are performed when P16 is high (LCD_DAT). The chip select is performed by P12 and reset by P8.
The first set-up call is
lcdExtenedFunctions() which sets the display into a command mode in order to set up a few parameters.
writeFunctionSet() exists in both the JS and C files.
This extension makes the Microbit hang up if I use the
shim=nokialcd::writeFunctionSet to make it use the C version of writeFunctionSet(). If I use the JS version of
writeFunctionSet() by removing the shim, the whole thing works.
If you look at the code in both the TS and CPP files,
writeFunction() is identical. It merely sets P12 and P16 to the appropriate states, calls
spi.write() with a value and then reverts P12 and P16.
Please note that spi.write() is also used in the function
writeSPIBuf() in the CPP file - this transfers the 504-byte buffer to the screen. This function works and I have tested it.
What is going on here? If I comment out the
spi.write(0x20 | (v << 1) | (h & 1)); line in writeFunctionSet, the init() routine completes. If I leave the line it, the Microbit hangs up at that point.