Block device peripheral and SBFS file system implemented.

Programs/loadable/hello.asm

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+; A program meant to be loaded off a disk rather than booted from.
+;
+; It is assembled for where it will live. Reserving the front of each segment puts the
+; first thing in it at a known address, and everything after that follows, so the labels
+; inside are already right for the place the loader will put it. Nothing relocates
+; anything: this works because the addresses here and the addresses in its header say the
+; same thing.
+;
+; The loader keeps below both of these, which is the whole of the arrangement.
+
+#Program
+
+  #Reserve 0x2000       ; This program's code lives from 0x2000.
+
+hello:
+  SETD.0 HelloText
+helloLoop:
+  LDA.0
+  BRA helloDone
+  OUTA 0x00
+  INCD.0
+  BRI helloLoop
+helloDone:
+  INIA 0x0A
+  OUTA 0x00
+  HALT
+
+#Data
+
+  #Reserve 0x1000       ; And its data from 0x1000.
+
+HelloText:
+"loaded off a disk, with a string and a loop of its own"