1 files changed, 60 insertions, 9 deletions
diff --git a/docs/TECH b/docs/TECH
index 00abf8805c..4532af3c42 100644
--- a/docs/TECH
+++ b/docs/TECH
@@ -15,15 +15,21 @@ Booting and (De)Scrambling
  scrambling that the original Archos firmware uses so that it can be loaded
  by the built-in firmware.
+  1) The built-in firmware starts
+  2) It looks in the root directory for a file called "archos.mod" (player)
+     or "ajbrec.ajz" (recorder)
+  3) If it finds one, it loads the file, descrambles it and runs it
 CPU
-  The CPU in use is a SH7034 from Hitachi, running at 11.0592MHz or 12MHz.
+  The CPU in use is a SH7034 from Hitachi, running at 11.0592MHz (recorder)
-  Most single instructions are excuted in 1 cycle. There is a 4KB internal ram
+  or 12MHz (player).
-  and a 2MB external ram.
+  Most single instructions are executed in 1 cycle. There is a 4KB internal RAM
+  and a 2MB external RAM.
 Memory Usage
-  All Archos Jukebox models have only 2MB ram. The ram is used for everything,
+  All Archos Jukebox models have only 2MB RAM. The RAM is used for everything,
  including code, graphics and config. To be able to play as long as possible
  without having to load more data, the size of the mpeg playing buffer must
  remain as big as possible. Also, since we need to be able to do almost
@@ -36,7 +42,50 @@ Playing MPEG
  The MPEG decoding is performed by an external circuit, MAS3507D (for the
  Player/Studio models) or MAS3587F (for the Recorder models).
-  ...
+  The CPU has a serial connection to the MAS for MP3 playback, using serial
+  port 0 at approx. 1mbit/s. The MAS has a handshake signal called DEMAND,
+  that informs the CPU when it wants more MP3 data. Whenever the DEMAND
+  signal goes high, it wants data sent over the serial line, and it wants it
+  quickly, within ~1ms. When the MAS has received enough data, it negates the
+  DEMAND signal and expects the incoming data stream to stop within 1ms.
+  The DEMAND signal is connected to a port pin on the CPU which can generate
+  an IRQ, but only on the falling edge. That means that the mpeg driver code
+� must poll the DEMAND signal every ms to keep the MAS happy. The mpeg code
+  does use the IRQ to detect the falling edge when the MAS is "full".
+  Unfortunately, the serial port on the CPU sends the LSB first, and the MAS
+  expects the MSB first. Therefore we have to revers the bit order in every
+  byte in the loaded MP3 data. This is referred to as "bit swapping" in the
+  Rockbox code.
+  The internal DMA controller is used to feed the serial port with data. The
+  driver works roughly like this:
+  1) Load MP3 data into the RAM buffer
+  2) Bitswap the data
+  3) Load the DMA source pointer to the next 64Kbyte block to be transferred
+  4) Wait until DEMAND is high
+  5) Enable the DMA
+  6) Wait until the falling DEMAND pin generates an IRQ
+  7) Disable the DMA
+  8) Go to 4
+  The DMA generates an IRQ when the 64Kbyte block is transferred, and the
+  IRQ handler updates the DMA source pointer.
+                    _____________________________
+                    |                           |
+  DEMAND  __________|                           |_____________
+                        _  _  _  _  _  _  _  _  _
+  SC0     _____________/ \/ \/ \/ \/ \/ \/ \/ \/ \____________
+                       \_/\_/\_/\_/\_/\_/\_/\_/\_/
+                      ^                         ^
+                      |                         |
+              Poll sees the DEMAND       The DEMAND pin generates
+              signal go high and         an IRQ that in turn disables
+              enables the DMA            the DMA again
 Spinning The Disk Up/Down
@@ -87,10 +136,12 @@ Playing a Directory
 Shuffle
  Since the playlist is a an array of indexes to where to read the file name,
-  shuffle modifies the order of these indexes in the array. The randomness is
+  shuffle modifies the order of these indexes in the array. The algorithm is
-  identical for the same random seed. This is the secret to good resume. Even
+  pretty much like shuffling a deck of cards, and it uses a pseudo random
-  when you've shut down your unit and re-starts it, using the same random seed
+  generator called the Mersenne Twister. The randomness is identical for the
-  as the previous time will give exactly the same random order.
+  same random seed. This is the secret to good resume. Even when you've shut
+  down your unit and re-starts it, using the same random seed as the previous
+  time will give exactly the same random order.
 Saving Config Data

diff --git a/docs/TECH b/docs/TECH index 00abf8805c..4532af3c42 100644 --- a/docs/TECH +++ b/docs/TECH
@@ -15,15 +15,21 @@ Booting and (De)Scrambling
15	scrambling that the original Archos firmware uses so that it can be loaded	15	scrambling that the original Archos firmware uses so that it can be loaded
16	by the built-in firmware.	16	by the built-in firmware.
17		17
		18	1) The built-in firmware starts
		19	2) It looks in the root directory for a file called "archos.mod" (player)
		20	or "ajbrec.ajz" (recorder)
		21	3) If it finds one, it loads the file, descrambles it and runs it
		22
18	CPU	23	CPU
19		24
20	The CPU in use is a SH7034 from Hitachi, running at 11.0592MHz or 12MHz.	25	The CPU in use is a SH7034 from Hitachi, running at 11.0592MHz (recorder)
21	Most single instructions are excuted in 1 cycle. There is a 4KB internal ram	26	or 12MHz (player).
22	and a 2MB external ram.	27	Most single instructions are executed in 1 cycle. There is a 4KB internal RAM
		28	and a 2MB external RAM.
23		29
24	Memory Usage	30	Memory Usage
25		31
26	All Archos Jukebox models have only 2MB ram. The ram is used for everything,	32	All Archos Jukebox models have only 2MB RAM. The RAM is used for everything,
27	including code, graphics and config. To be able to play as long as possible	33	including code, graphics and config. To be able to play as long as possible
28	without having to load more data, the size of the mpeg playing buffer must	34	without having to load more data, the size of the mpeg playing buffer must
29	remain as big as possible. Also, since we need to be able to do almost	35	remain as big as possible. Also, since we need to be able to do almost
@@ -36,7 +42,50 @@ Playing MPEG
36	The MPEG decoding is performed by an external circuit, MAS3507D (for the	42	The MPEG decoding is performed by an external circuit, MAS3507D (for the
37	Player/Studio models) or MAS3587F (for the Recorder models).	43	Player/Studio models) or MAS3587F (for the Recorder models).
38		44
39	...	45	The CPU has a serial connection to the MAS for MP3 playback, using serial
		46	port 0 at approx. 1mbit/s. The MAS has a handshake signal called DEMAND,
		47	that informs the CPU when it wants more MP3 data. Whenever the DEMAND
		48	signal goes high, it wants data sent over the serial line, and it wants it
		49	quickly, within ~1ms. When the MAS has received enough data, it negates the
		50	DEMAND signal and expects the incoming data stream to stop within 1ms.
		51
		52	The DEMAND signal is connected to a port pin on the CPU which can generate
		53	an IRQ, but only on the falling edge. That means that the mpeg driver code
		54	� must poll the DEMAND signal every ms to keep the MAS happy. The mpeg code
		55	does use the IRQ to detect the falling edge when the MAS is "full".
		56
		57	Unfortunately, the serial port on the CPU sends the LSB first, and the MAS
		58	expects the MSB first. Therefore we have to revers the bit order in every
		59	byte in the loaded MP3 data. This is referred to as "bit swapping" in the
		60	Rockbox code.
		61
		62	The internal DMA controller is used to feed the serial port with data. The
		63	driver works roughly like this:
		64
		65	1) Load MP3 data into the RAM buffer
		66	2) Bitswap the data
		67	3) Load the DMA source pointer to the next 64Kbyte block to be transferred
		68	4) Wait until DEMAND is high
		69	5) Enable the DMA
		70	6) Wait until the falling DEMAND pin generates an IRQ
		71	7) Disable the DMA
		72	8) Go to 4
		73
		74	The DMA generates an IRQ when the 64Kbyte block is transferred, and the
		75	IRQ handler updates the DMA source pointer.
		76
		77
		78	_____________________________
		79	\| \|
		80	DEMAND __________\| \|_____________
		81	_ _ _ _ _ _ _ _ _
		82	SC0 _____________/ \/ \/ \/ \/ \/ \/ \/ \/ \____________
		83	\_/\_/\_/\_/\_/\_/\_/\_/\_/
		84	^ ^
		85	\| \|
		86	Poll sees the DEMAND The DEMAND pin generates
		87	signal go high and an IRQ that in turn disables
		88	enables the DMA the DMA again
40		89
41	Spinning The Disk Up/Down	90	Spinning The Disk Up/Down
42		91
@@ -87,10 +136,12 @@ Playing a Directory
87	Shuffle	136	Shuffle
88		137
89	Since the playlist is a an array of indexes to where to read the file name,	138	Since the playlist is a an array of indexes to where to read the file name,
90	shuffle modifies the order of these indexes in the array. The randomness is	139	shuffle modifies the order of these indexes in the array. The algorithm is
91	identical for the same random seed. This is the secret to good resume. Even	140	pretty much like shuffling a deck of cards, and it uses a pseudo random
92	when you've shut down your unit and re-starts it, using the same random seed	141	generator called the Mersenne Twister. The randomness is identical for the
93	as the previous time will give exactly the same random order.	142	same random seed. This is the secret to good resume. Even when you've shut
		143	down your unit and re-starts it, using the same random seed as the previous
		144	time will give exactly the same random order.
94		145
95	Saving Config Data	146	Saving Config Data
96		147