U-Boot supports "standalone" applications, which are loaded dynamically;
these applications can have access to the U-Boot console I/O functions,
memory allocation and interrupt services.
A couple of simple examples are included with the U-Boot source code:
examples/hello_world.c contains a small "Hello World" Demo
application; it is automatically compiled when you build U-Boot. It's
configured to run at address 0x00040004, so you can play with it like
that:
=> loads
## Ready for S-Record download ...
~>examples/hello_world.srec
1 2 3 4 5 6 7 8 9 10 11 ...
[file transfer complete]
[connected]
## Start Addr = 0x00040004
=> go 40004 Hello World! This is a test.
## Starting application at 0x00040004 ...
Hello World
argc = 7
argv[0] = "40004"
argv[1] = "Hello"
argv[2] = "World!"
argv[3] = "This"
argv[4] = "is"
argv[5] = "a"
argv[6] = "test."
argv[7] = ""
Hit any key to exit ...
## Application terminated, rc = 0x0
Alternatively, you can of course use
TFTP to download the image over the network.
In this case the binary image (
hello_world.bin) is used.
Note that the entry point of the program is at offset 0x0004 from the start of file, i. e.
the download address and the entry point address differ by four bytes.
=> tftp 40000 /tftpboot/hello_world.bin
...
=> go 40004 This is another test.
## Starting application at 0x00040004 ...
Hello World
argc = 5
argv[0] = "40004"
argv[1] = "This"
argv[2] = "is"
argv[3] = "another"
argv[4] = "test."
argv[5] = ""
Hit any key to exit ...
## Application terminated, rc = 0x0
This example is only available on MPC8xx
CPUs.
This example, which demonstrates how to register a
CPM interrupt
handler with the U-Boot code, can be found in
examples/timer.c. Here, a
CPM timer is set up to generate an
interrupt every second. The interrupt service routine is trivial, just
printing a '.' character, but this is just a demo program. The
application can be controlled by the following keys:
? - print current values of the CPM Timer registers
b - enable interrupts and start timer
e - stop timer and disable interrupts
q - quit application
=> loads
## Ready for S-Record download ...
~>examples/timer.srec
1 2 3 4 5 6 7 8 9 10 11 ...
[file transfer complete]
[connected]
## Start Addr = 0x00040004
=> go 40004
## Starting application at 0x00040004 ...
TIMERS=0xfff00980
Using timer 1
tgcr @ 0xfff00980, tmr @ 0xfff00990, trr @ 0xfff00994, tcr @ 0xfff00998, tcn @ 0xfff0099c, ter @ 0xfff009b0
Hit 'b':
[q, b, e, ?] Set interval 1000000 us
Enabling timer
Hit '?':
[q, b, e, ?] ........
tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0xef6, ter=0x0
Hit '?':
[q, b, e, ?] .
tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x2ad4, ter=0x0
Hit '?':
[q, b, e, ?] .
tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x1efc, ter=0x0
Hit '?':
[q, b, e, ?] .
tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x169d, ter=0x0
Hit 'e':
[q, b, e, ?] ...Stopping timer
Hit 'q':
[q, b, e, ?] ## Application terminated, rc = 0x0
