Added new file and README

boot_block/README

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+The files here are 'production' versions of system code:
+
+bootstrap_tty.asm
+    The TTY bootstrap ROM code created from the data in file
+    images/imlacdocs/loading.pdf.
+
+blockloader_c8lds_ptr_tty.asm
+    The blockloader for c8lds format files found in iasm/chars.ptp.
+
+blockloader_lc16sd_tty.asm
+    The blockloader for lc16sd format files found in bin/munch.ptp.

boot_block/bootstrap_tty.asm

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+;------------------------
+; TTY bootstrap code from images/imlacdocs/loading.pdf
+;------------------------
+                        ;
+bladdr  equ     037700  ; address of top mem minus 0100
+blsize  equ     0100    ; size of blockloader code
+                        ;
+	ORG	040	;
+                        ;
+	LAC	staddr	;
+	DAC	010	; 010 points to loading word
+	LWC	blsize-2;
+	DAC	020	; 020 is ISZ counter of loader size
+; skip all bytes until the expected byte
+skpzer	RCF		; 
+	CAL		;
+	RSF		; wait for next byte
+	JMP	.-1	;
+	RRB		; get next TTY byte
+	SAM	fbyte	; wait until it's the expected byte
+	JMP	skpzer	;
+nxtwrd	RSF		; wait until TTY byte ready
+	JMP	.-1	;
+	RRC		; get high byte and clear flag
+	RAL	3	; shift into AC high byte
+	RAL	3	;
+	RAL	2	;
+	RSF		; wait until next TTY byte
+	JMP	.-1	;
+	RRC		; get low byte and clear flag
+	DAC	*010	; store word
+	CAL		; clear AC ready for next word
+	ISZ	020	; finished?
+	JMP	nxtwrd	; jump if not
+	JMP	*blstrt	; else execute the blockloader
+                        ;
+	DATA	000000	; empty space?
+	DATA	000000	;
+	DATA	000000	;
+	DATA	000000	;
+                        ;
+fbyte	DATA	000002	; expected first byte of block loader
+blstrt	data	bladdr	; start of blockloader code
+staddr	data	bladdr-1; ISZ counter for blockloader size
+                        ;
+	END		;