updated readme.

README.md

@@ -5,7 +5,7 @@ A kernel module that will (one day) power the CC2520 802.15.4 radio in Linux.
 
 The general idea is to create a character driver that exposes 802.15.4 frames
 to the end user, allowing them to test and layer different networking stacks
-from user-land onto the CC2520 radio. We're specifically targetting running
+from user-land onto the CC2520 radio. We're specifically targeting running
 the IPv6 TinyOS networking stack on a Raspberry Pi.
 
 To compile you'll need an ARM cross compiler and the source tree of a compiled
@@ -16,13 +16,59 @@ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-
 
 Please note that we're cross-compiling from an x86 machine.
 
+Installing
+----------
+
+The installation process for this has gotten a little more involved as I continue
+to tweak things for performance. You'll need to be running the 3.6 kernel from
+the Raspberry Pi's GitHub (not the 3.2 standard version).
+
+This requires cross-compiling the kernel from source. To do this I started with
+the standard Raspbian image and replaced the kernel, modules, and firmware using
+the steps from the "How to Compile from Source" page. 
+
+You need the 3.6 kernel because we're using a newer SPI driver. This driver
+supports a real-time workqueue and is interrupt driven. You can find
+it here:
+
+https://raw.github.com/msperl/linux/73afedc07e3b94d8b9d588912faf26081178d268/drivers/spi/spi-bcm2708.c
+
+You'll need to replace the current driver file, as well as modify the board
+configuration to enable the DMA parts of it.
+
+Finally this driver needs a small patch because nobody seems to implement
+chip-select toggling behavior correctly:
+
+	if (!(flags | FLAGS_LAST_TRANSFER)) {
+		bs->cs|=SPI_CS_TA|SPI_CS_INTR|SPI_CS_INTD;
+	}
+
+will become
+
+	if (!(flags | FLAGS_LAST_TRANSFER)) {
+		bs->cs|=SPI_CS_INTR|SPI_CS_INTD;
+	}	
+
+Not keeping the SPI_CS_TA flag active will have the SPI driver toggle
+the CS pin between transmissions. The CC2520 radio requires a SPI
+toggle to terminate command sequences that don't have a predetermined
+length. 
+
+*Eventually I'll try to make this a easier once things stabilize a little
+bit. Sorry it's so chaotic!*
+
+Current Status
+---------------
+The driver currently sends and receives packets! We get close to the maximum
+theoretical transmission rate supported by the CC2520, which is just fantastic.
+
+Work is currently focused on implementing LPL and automatic software
+acknowledgements. The goal is to push as much as possible into userland
+but some things need to be implemented in the kernel to enable strict
+timing guarantees. 
+
 Some notes
 ----------
-  * You'll need to load the spi-bcm2708 driver for this module to work. You can do this with modprobe spi-bcm2708.
-  * I made a small patch to the spi-bcm2708 driver. It previously didn't allow leaving the CS line high after a spi_message completed:
-  	spi-bcm2709.c:315:
-	if (xfer->cs_change) {
-	//if (list_is_last(&xfer->transfer_list, &msg->transfers) ||
-	//		xfer->cs_change) {
+  * You'll need to load the spi-bcm2708 driver for this module to work. You can do this by commenting out the line in the blacklisted modules file found in /etc.
   * Make sure to update the directory for the kernel in the Makefile
   * Update the GPIO defs in cc2520.h