avrpgm: add EEPROM support

also, verify all 3 first bytes of SPI commands. I'm not sure why
I wasn't doing that, probably because I was getting a lot of AVR
err and thought that only 2 bytes of the cmd were echoed. But now,
with a reliable SPI setup, verifying 3 bytes seems to work.

blk/160

@@ -1,4 +1,4 @@
-( AVR Programmer, load range 160-162. doc/avr.txt )
+( AVR Programmer, load range 160-163. doc/avr.txt )
 ( page size in words, 64 is default on atmega328P )
 CREATE aspfpgsz 64 ,
 VARIABLE aspprevx
@@ -6,7 +6,7 @@ VARIABLE aspprevx
 : _xc ( a -- b ) DUP (spix) ( a b )
     DUP aspprevx @ = NOT IF ABORT" AVR err" THEN ( a b )
     SWAP aspprevx ! ( b ) ;
-: _cmd ( b4 b3 b2 b1 -- r4 ) _xc DROP _x DROP _xc DROP _x ;
+: _cmd ( b4 b3 b2 b1 -- r4 ) _xc DROP _xc DROP _xc DROP _x ;
 : asprdy ( -- ) BEGIN 0 0 0 0xf0 _cmd 1 AND NOT UNTIL ;
 : asp$ ( spidevid -- )
     ( RESET pulse ) DUP (spie) 0 (spie) (spie)

blk/163

@@ -0,0 +1,6 @@
+: aspe@ ( addr -- byte, read from EEPROM )
+    0 SWAP 256 /MOD ( 0 lsb msb ) SWAP
+    0xa0 ( 0 msb lsb 0xa0 ) _cmd ;
+: aspe! ( byte addr --, write to EEPROM )
+    256 /MOD ( b lsb msb ) SWAP
+    0xc0 ( b msb lsb 0xc0 ) _cmd DROP asprdy ;

doc/avr.txt

@@ -103,3 +103,10 @@ aspfb! that divides dst addr by 2 because AMOVEW use byte-based
 addresses but aspfb! uses word-based ones. You also have to make
 sure that A@* points to @ (or another word-based fetcher)
 instead of its default value of C@.
+
+# Access EEPROM
+
+Accessing EEPROM is simple and is done byte-by-byte with words
+aspe@ and aspe!. Example:
+
+0x42 0 aspe! 0 aspe@ .x ( prints 42 )

recipes/rc2014/avr.md

@@ -27,8 +27,8 @@ the "no division" position, and when I communicate with the
 AVR chip, I move the switch to increase the divisor.
 
 Once you've done this, you can test that you can communicate
-with your AVR chip by doing `160 162 LOADR` (turn off your
-programmer or alse it might mess up the SPI bus and prevent you
+with your AVR chip by doing `160 163 LOADR` (turn off your
+programmer or else it might mess up the SPI bus and prevent you
 from using your SD card) and then running:
 
     1 asp$ aspfl@ .x 0 (spie)