Enable framebuf module and fix SSD1306 driver to work with hardware I2C #15
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jepler
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Oct 1, 2020
It was incorrect to NULL out the pointer to our heap allocated buffer in `reset`, because subsequent to framebuffer_reset, but while the heap was still active, we could call `get_bufinfo` again, leading to a fresh allocation on the heap that is about to be destroyed. Typical stack trace: ``` #1 0x0006c368 in sharpdisplay_framebuffer_get_bufinfo #2 0x0006ad6e in _refresh_display #3 0x0006b168 in framebufferio_framebufferdisplay_background #4 0x00069d22 in displayio_background adafruit#5 0x00045496 in supervisor_background_tasks adafruit#6 0x000446e8 in background_callback_run_all adafruit#7 0x00045546 in supervisor_run_background_tasks_if_tick adafruit#8 0x0005b042 in common_hal_neopixel_write adafruit#9 0x00044c4c in clear_temp_status adafruit#10 0x000497de in spi_flash_flush_keep_cache adafruit#11 0x00049a66 in supervisor_external_flash_flush adafruit#12 0x00044b22 in supervisor_flash_flush adafruit#13 0x0004490e in filesystem_flush adafruit#14 0x00043e18 in cleanup_after_vm adafruit#15 0x0004414c in run_repl adafruit#16 0x000441ce in main ``` When this happened -- which was inconsistent -- the display would keep some heap allocation across reset which is exactly what we need to avoid. NULLing the pointer in reconstruct follows what RGBMatrix does, and that code is a bit more battle-tested anyway. If I had a motivation for structuring the SharpMemory code differently, I can no longer recall it. Testing performed: Ran my complicated calculator program over multiple iterations without observing signs of heap corruption. Closes: adafruit#3473
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We should enable the framebuf module to build in support for a framebuffer and basic font that's used by the SSD1306 (OLED wing) module. Enabling framebuf just requires adding this to the mphalconfigport.h:
However the SSD1306 driver (in drivers/display) doesn't work with SAMD21's I2C interface because it uses low level I2C start and stop bits to manually construct a transaction. This is fine for the ESP port with software I2C, but most hardware I2C interfaces don't support it so we need to do something else.
My quick thought is to expand the size of the framebuffer the SSD1306 class allocates so that it can include the extra address register byte sent before the buffer data: https://github.com/adafruit/micropython/blob/master/drivers/display/ssd1306.py#L118-L121 Then have the SSD1306 class read and write framebuffer data 1 byte shifted up so that it can blast out the framebuffer including address byte in one SPI write transaction.
Not a high priority, for now OLED feather wing support can wait for this fix.
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