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I got PIC32 starter kit today. Here are some impressions:
- Comes with eval version of C32 C-compiler with 64KB code size limit. C32
is actually called C32-gcc, so it's a gcc derivative. The source is on
the website, but who knows if it's recent or complete.
- Hardware debugging (breakpoints, goto cursor) works in MPLAB on this
little board, but I found that sometimes it gets into a mode where it
thinks that breakpoints are not supported: "breakpoint limit for hardware
is 0" in the breakpoint dialogue. This is fixed if you restart MPLAB.
Anyway, you can view both assembly and C source during single-stepping.
It's pretty nice.
- You can DBPRINTF over JTAG (and also DBGETS). It's very slow. It was not
documented that you had to add a define to make this work for new projects
(-DPIC32_START_KIT- add the define in Project->Build
Options->Project->C-compiler->Macros). The debug I/O library is not part
of the main library- it was just a db_utils.a file (no source) in the
StartKitTutorial directory (the "hello world" program).
I had to copy it to the timer interrupt demo program that I wanted to try
to get it working. I then had to replace all the UART I/O calls to debug
I/O calls. There is no UART interface on the starter board, so they must
be designing these demos for some other board (actually they are labs for
a course- maybe FAE or early customer training?)
One annoying thing about this form of JTAG I/O (which is not unique to
PIC)- it's not a real serial port. When you call DBGETS, a window pops up
in MPLAB for you to type a string. This is a modal window, so you can not
actually halt the debugger when it is up. So don't put DBGETS in a loop!
There is no way to poll for keyboard input. When the DBGETS is waiting
for input, the CPU is basically break-point halted, so interrupts stop
running.
- This is how you make interrupt handlers:
void __ISR(TIMER_1_VECTOR, ipl2) my_handler(void)
{
mPORTDToggleBits(BIT_0); // Blink a led
mT1ClearIntFlag();
}
And that's about it (set up the timer and EnableIntT1). You do not have to
explicity write the my_handler address to a vector, the compiler just does
it.
- The IDE needs a little work. There were some screen update glitches when
I closed various windows. It core dumped when switching projects. The
manual for the C-libraries (particularly the peripherals) is missing.
- On the other hand, things did generally work. You basically hit F10 to
compile and F9 to run. It prompts you for downloading the code to the
board.
- There are compiler settings for making compressed MIPS 16-bit code (like
the ARM thumb code). Both worked. Last time I used MIPS, there was no
16-bit option.
Some notes about the PIC32 CPU:
- Someone complained that the chip has only 16-bit timers: this is not
exactly true: timers can be paired up to form single 32-bit timers.
- There is a RTC clock generator (and an RTCC block) on the chip with pins
for a 32 KHz crystal.
- There is support for some kind of external trace buffer on the CPU. You
must have to buy some special ICE to make use of it.
- The code examples include HTML server on a TCP/IP stack, but they need a
board with Microchip's ethernet to SPI interface chip.
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