RedBoot Extensions — Usage
The Raspberry Pi version of RedBoot provides a number of extensions to the standard RedBoot behaviour. These include the execution of a startup script and some extra commands.
Unlike most RedBoot instances, the Raspberry Pi always has access to a storage device containing a file system. It is also useful for JTAG debugging to be able to have some dynamic hardware initialization. So, on startup RedBoot attempts to mount the boot partition on the SD card and execute the contents of a script file.
The script file is named
and consists of a sequence of RedBoot commands separated by
newlines. Blank lines are ignored. Comments are introduced
by the a hash character (
#) and extend to
the end of the current line.
RedBoot waits 1 second before executing the script, during
which time the user may type a Ctrl-C character to abort
execution of the script. This time may be changed by
rebuilding RedBoot with a different
Other ports of RedBoot are typically flash memory resident
and use the flash as a persistant store for RedBoot
configuration information and files. You will find these
areas referred to as the fconfig area and flash image
system (FIS) within the
redboot.txt script file can
contain any standard RedBoot command, as well as the
additional Raspberry Pi commands described below, you can
use it to configure any settings that would normally be
stored in the fconfig area. For example, you could set a
static IP address for the board with the
ip_address -l 192.168.1.100/24
To modify the
simply mount the SD card on a PC. You will find
redboot.txt in the root directory of the
The info command provides information about the current Raspberry Pi board. RedBoot, and eCos, discover the type of board and its properties at runtime. This command reports what has been found out. As an example, the output for a Pi3 would appear as follows:
RedBoot> info Board Model = 00000000 Board Revision = 00a02082 Model = B3 CPU = BCM2837 - Cortex-A53 RAM = 1024MiB Flags = 07 Ethernet WiFi Bluetooth Board Serial = 000000009330d07b MAC Address = b8:27:eb:30:d0:7b SDRAM Size = 3d000000 Clocks: ARM = 600000000 Hz Core = 250000000 Hz Timer = 1000000 Hz UART0 = 48000000 Hz EMMC = 250000000 Hz RedBoot>
And for a CM1:
RedBoot> info Board Model = 00000000 Board Revision = 00000011 Model = CM1 CPU = BCM2835 - ARM11 RAM = 512MiB Flags = 08 eMMC Board Serial = 00000000604ab22b MAC Address = b8:27:eb:4a:b2:2b SDRAM Size = 1e000000 Clocks: ARM = 700000000 Hz Core = 250000000 Hz Timer = 1000000 Hz UART0 = 48000000 Hz EMMC = 250000000 Hz RedBoot>
The gpio command provides information and control of the GPIO pins available in the BCM283X. The command supports a number of sub-commands:
- gpio get [pin]
- Print the state of a given GPIO pin, or if no pin is given, it prints the state of all pins. The information printed for each pin includes the alternate function value and the name of the function selected, mode setting bits, and the current input level.
- gpio in <pin>
- Reports the current input level of the pin, 0 or 1.
- gpio monitor [-m <msec>] <pin>
Monitor a given pin for changes and print the value
every second. The
-moption allows the monitoring interval to be changed to the given number of milliseconds.
- gpio out -0|-1 <pin>
Set the output of the given pin to 0
-0) or 1 (
-1). The pin may need to be set to output mode with gpio set before any effect can be seen.
- gpio set [-i|-o|-a <alt>] <pin>
Set the function of a given pin. It can be set to
INPUT with the
-ioption, OUTPUT with the
-ooption or to one of six alternate function with the
- gpio table
- Print a table of all GPIO pins and the names of the alternate functions they can take. The current setting of the pin is indicated by an asterisk against the relevant alternate setting. If no asterisk is present then the pin is in GPIO mode.
- gpio toggle [-m <msec>] <pin>
Toggle a pin at a 1 second period with a 50% duty
-moption allows the toggling to occur with the given period in milliseconds. The pin may need to be set to output mode with gpio set before any effect can be seen.
The jtag command provides direct support for setting up the JTAG debug pins and querying their state. The arguments to this command are a list of pin numbers. Each of these GPIO pins is put into its JTAG function. Only those pins that can be used for JTAG operation may be entered; at present these are GPIO4 to GPIO6, GPIO12, GPIO13 and GPIO22 to GPIO27. On completion the command lists the pins that are in JTAG mode. If no pins are given, then the current JTAG pin assignments are listed. There is no mechanism for disabling a JTAG pin, if it is to be used for some other purpose then it will be reinitialized as part of that functionality.
The selection of JTAG pins to use may depend on the functionality of any HATs or other hardware attached to the GPIO header. It may be necessary to mix and match pins to get a complete set. In some situations it may not be possible to find a set of pins that will work, in which case you may need to use serial debugging only.
The following table defines the possible GPIO pin alternatives for the JTAG signals, as well as their mapping on to the 40-way expansion bus used on standard RPi boards. Each JTAG signal has two alternative mappings, apart from TRST which can only be set to GPIO pin 22. Note that RTCK is not required or supported by all JTAG debuggers and may not need to be set.
|JTAG Signal||Alt 4 GPIO pin||(Alt 4 40-way pin)||Alt 5 GPIO pin||(Alt 5 40-way pin)|
For example, the jtag command used in the default redboot.txt file, sets and reports the BCM pins as follows:
RedBoot> jtag 4 22 24 25 27 PIN FUNC 22 ARM_TRST 23 ARM_RTCK 24 ARM_TDO 25 ARM_TCK 26 ARM_TDI 27 ARM_TMS
The led command controls the behaviour of
the board's ACT LED. By default RedBoot blinks the LED at 1
Hz with a 50% duty cycle; this serves as an indicator that
RedBoot is up and running when the serial line is not
connected. It takes one of three argument values.
on disables blinking and switches the
off also disables blinking
and switches the LED off.
re-enables the 1Hz blinking. Note that these setting only
apply when RedBoot is running. Once and application has been
loaded and is running, control of the LED passes to it.
The usb command prints out some information from the USB stack. This includes some gathered statistics and information on each of the USB devices currently attached to the USB bus.
|2018-07-06||eCosPro Non-Commercial Public License|