Update shell/blkdev docs

doc/blockdev.md

@@ -38,13 +38,13 @@ they should try to adhere to the convention, that is:
 
 ## Shell usage
 
-`blockdev.asm` supplies 2 shell commands that you can graft to your shell thus:
+`blockdev.asm` supplies 4 shell commands that you can graft to your shell thus:
 
     [...]
-    SHELL_EXTRA_CMD_COUNT	.equ	2
+    SHELL_EXTRA_CMD_COUNT	.equ	4
     #include "shell.asm"
     ; extra commands
-    .dw	blkBselCmd, blkSeekCmd
+    .dw	blkBselCmd, blkSeekCmd, blkLoadCmd, blkSaveCmd
     [...]
 
 ### bsel
@@ -62,6 +62,18 @@ The device position is device-specific: if you seek on a device, then switch
 to another device and seek again, your previous position isn't lost. You will
 still be on the same position when you come back.
 
+### load
+
+`load` works a bit like `poke` except that it reads its data from the currently
+active blockdev at its current position. If it hits the end of the blockdev
+before it could load its specified number of bytes, it stops. It only raises an
+error if it couldn't load any byte.
+
+### save
+
+`save` is the opposite of `load`. It writes the specified number of bytes from
+memory to the active blockdev at its current position.
+
 ### Example
 
 Let's try an example: You glue yourself a Collapse OS with ACIA as its first
@@ -70,7 +82,7 @@ could do to copy memory around:
 
     > mptr d000
     D000
-    > load 4 [device 0 is selected initially]
+    > poke 4
     [enter "abcd"]
     > peek 4
     61626364
@@ -83,7 +95,7 @@ could do to copy memory around:
     [returns immediately]
     > peek 4
     61626364
-    > seek 0002
+    > seek 00 0002
     > load 2
     > peek 4
     63646364

doc/shell.md

@@ -19,7 +19,7 @@ smaller than `0x10`. Example calls:
 
     mptr 01ff
     peek 4
-    load 1f
+    poke 1f
     call 00 0123
 
 All numbers printed by the shell are in hexadecimals form.
@@ -56,20 +56,16 @@ bytes we want to read. Example:
     > peek 2
     ED56
 
-## load
+## poke
 
 Puts the serial console in input mode and waits for a specific number of
 characters to be typed (that number being specified by a byte argument). These
 characters will be literally placed in memory, one after the other, starting at
 `memptr`.
 
-This command is, for now, of limited use because it's tied to the active
-console, but a method for selecting I/O sources is planned and this command will
-become much more useful.
-
 Example:
 
-    > load 5
+    > poke 5
     Hello
     > peek 5
     48656C6C6F