[minor] -docs

ipxe · Mar 3, 2011 · f6b9336 · f6b9336
1 parent f928016
commit f6b9336
Showing 1 changed file with 17 additions and 13 deletions.
diff --git a/doc/raw.txt b/doc/raw.txt
@@ -1,31 +1,33 @@
-The raw format of the pulseblaster executable is  a sequence of 10-byte "VLIW" instructions.
-(These are normally generated by the separate tool pb_asm, part of pb_utils).
+The VLIW format (see vliw.txt) is a simple representation of an ideal pulseblaster. In order to actually program it, 
+we need to convert each VLIW instruction into a sequence of 10 bytes, which are actually written to the device.
+This final stage would generate a .bin file; pb_asm converts VLIW to BIN; pb_prog goes direct from VLIW to the hardware.
 
-Consider the following VLIW instruction:
+This is the process:
+
+(1) Consider the following VLIW instruction:
 
 #OUTPUT         OPCODE  ARG	 LENGTH
 0xffeedd        CALL	0x88776  0xccbbaa99
 
-The assembler, pb_asm does the following:
-
-- Opcodes are converted from strings to numbers (as defined in pulseblaster.h)
-  [In this case, CALL = 0x4 ]
 
-- Lengths are corrected, eg subtraction of PB_INTERNAL_LATENCY.
-  [In this example, length becomes 0xccbbaa96 ]
+(2) This is read in by pb_prog, tokenised by pb_parse_sourceline() and then merged by pb_make_vliw() in src/pb-functions.inc
 
-- The VLIW is is split up into 10 bytes:
+  - Opcodes are converted from strings to numbers (as defined in pulseblaster.h)
+		[In the example, CALL = 0x4 ]
+  - If ARG is '-', it is converted to 0.
+  - Offsets are corrected, eg subtraction of PB_INTERNAL_LATENCY.
+		[In this example, length becomes 0xccbbaa96 ]
+  - It is split up into 10 bytes:
 
-
-The bytes are these:
+(3) The bytes are these:
 
   3       bytes of output
   2 1/2   bytes for arg
   1/2 	  byte  for opcode
   4 	  bytes for the delay.
 
 
-Thus, we actually get the following series of writes, in this order
+(4) Thus, we actually get the following series of writes, in this order
 
   0xff		MSB	}	
   0xee			} 3 byte output
@@ -41,3 +43,5 @@ Thus, we actually get the following series of writes, in this order
   0x96		LSB	}
 
 
+(5) For more info, read the source of pb_prog.c. It's quite simple.
+