loadp2/flash_stub.spin2 at master · totalspectrum/loadp2 · GitHub

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' *** SPI FLASH BOOT LOADER
' based on Chip Gracey's original flash loader,
' but simplified and made more independent for
' loadp2 purposes
'
CON	spi_cs = 61
	spi_ck = 60
	spi_di = 59
	spi_do = 58

DAT

'************
'*  Loader  *
'************
'
' The ROM booter reads this code from the 8-pin SPI flash from $000000..$0003FF, into cog
' registers $000..$0FF. If the booter verifies the 'Prop' checksum, it does a 'JMP #0' to
' execute this loader code.
'
' The initial application data trailing this code in registers app_start..$0FF are moved to
' hub RAM, starting at $00000. Then, any additional application data are read from the flash
' and stored into the hub, continuing from where the initial application data left off.
'
' On entry, both spi_cs and spi_ck are low outputs and the flash is outputting bit 7 of the
' byte at address $400 on spi_do. By cycling spi_ck, any additional application data can be
' received from spi_do.
'
' Once all application data is in the hub, an application checksum is verified, after which
' cog 0 is restarted by a 'COGINIT #0,#$00000' to execute the application. If that checksum
' fails, due to some data corruption, the SPI pins will be floated and the clock stopped
' until the next reset. As well, a checksum is verified upon initial download of all data,
' before programming the flash. This all ensures that no errant application code will boot.
'
		org
'
'
' First, move application data in cog app_start..$0FF into hub $00000+
'
loader
x		jmp	#real_start	' re-used as temporary variable
propchksum	long	0		' magic value to make first 1K add to "Prop" (filled by loadp2)
app_longs	long	0		' number of longs (filled by loadp2)

real_start
'
'
' Read in remaining application longs
'
		wrpin	#%01_00101_0,#spi_ck	'set spi_ck smart pin for transitions, drives low
		fltl	#spi_ck			'reset smart pin
		wxpin	#1,#spi_ck		'set transition timebase to clk/1
		drvl	#spi_ck			'enable smart pin

		setxfrq	clk2			'set streamer rate to clk/2

		wrfast	#0,#0			'ready to write to hub at application start

.block		bmask	x,#10			'try max streamer block size for longs ($7FF)
		fle	x,app_longs		'limit to number of longs left
		sub	app_longs,x		'update number of longs left

		shl	x,#5			'get number of bits
		setword	wmode,x,#0		'insert into streamer command
		shl	x,#1			'double for number of spi_ck transitions

		wypin	x,#spi_ck		'2	start spi_ck transitions
		waitx	#3			'2+3	align spi_ck transitions with spi_do sampling
		xinit	wmode,#0		'2	start inputting spi_do bits to hub, bytes-msb-first
		waitxfi				'?	wait for streamer to finish

		tjnz	app_longs,#.block	'if more longs left, read another block


		' shut down smart pins to leave them
		' in known state for app
		fltl	#spi_do addpins 3	'float all pins
		wrpin	#0,#spi_ck		'clear spi_ck smart pin mode

{ FIXME DEBUG
		drvl	#56
		waitx	##40_000_000
		drvl	#57
		waitx	##40_000_000
		drvh	#56
		waitx	##40_000_000
}
		waitx	##2_000_000		'pause a bit
		coginit	#0,#$00000		'run application
'
'
' Data
'
clk2		long	$4000_0000		'clk/2 nco value for streamer
wmode		long	$C081_0000 + spi_do<<17	'streamer mode, 1-pin input, bytes-msb-first, bytes to hub

		fit	$100	     		' must fit in 1K