Rewrite flash.c for less size
Add cache for check checksum (more faster interpolate, used in multi segments sweep)
More fixes for font and select size of marker icon
More debug functions
For enable use external (LSE) clock generator need un comment in Makefile
#UDEFS+= -DVNA_USE_LSE
By default use internal (LSI) clock generator, but it stop then VNA power off
For enable use external (LSE) clock generator, need install 32.768kHz clock quartz on PC14 and PC15 pins, it allow clock run while power off
For enable use RTC in code uncomment in nanovna.h
#define __USE_RTC__
This enable command 'time'
usage: time [y|m|d|h|min|sec] 0-99
Example set 2020 year run 'time y 20'
Add show current time in version screen
Better use font size constants for all screen size
Cleanup and optimize code
Add comments, fix definitions
Fix rounding errors
Fix band 1 stability
mcuconf.h
Set I2C bus clock to SYSCLK (more fast)
Apply 400kHz bus I2C clock timings for 8MHz and 48Mhz clock
main.c
Remove and reset some variables
Add separate sweep for calibration (allow calibrate if sweep paused)
Increase main thread stack (need for run calibrate, possibly need execute some commands in sweep threads for reduce stack usage)
Rework display spi driver:
use DMA for read, write
add blitBitmap functions
Use DMA for color fill
More correct SPI bus control
Move color definitions to nanovna.h
Some code optimization for speed and size (save about 3k bytes)
Change grid Y resolution to 10
Fix convert from float to int (fix some rounding errors on plot)
Disable unused HAL serial
Change battery icon
