On Tue, 25 May 2021 09:45:39 -0700, in gmane.comp.hardware.beagleboard.user "John Dammeyer" <johnd-5o6ditlojsohvde0pjs...@public.gmane.org> wrote:
> >Here's the BBB version from and you can see the code is identical for both the >Pi and the Beagle. >https://github.com/derekmolloy/exploringBB/blob/version2/chp08/spi/spidev_test/spidev_test.c >============================================================================================== >uint8_t rx[ARRAY_SIZE(tx)] = {0, }; > struct spi_ioc_transfer tr = { > .tx_buf = (unsigned long)tx, > .rx_buf = (unsigned long)rx, Somewhat confusing code -- one has to track upwards in the code... C arrays are a synonym for pointers, so he's using unsigned long to store a pointer to the array. I'm not downloading the source again to see how the buffers are defined... > > Data.tx_buf := PtrUInt(WriteBuffer); > Data.rx_buf := PtrUInt(ReadBuffer); ... just notice this explicitly asks for a pointer (given my stale C history, I'd tend to read that as a pointer to an unsigned integer of some size... But the C version has the buffers defined as uint8_t (new in C99/C++11) with is an 8-bit unsigned (equivalent to old unsigned char). Does FreePascal have size differentiation? >It's likely the C compiler clears this structure when it's declared or extends >0's out on an assignment that isn't done by the FreePascal compiler. And that >it was required in that Pi forum posting for C code suggests it's perhaps even >somewhat random. Compiler flags maybe? """ -fno-zero-initialized-in-bss If the target supports a BSS section, GCC by default puts variables that are initialized to zero into BSS. This can save space in the resulting code. """ is the closest GCC option I saw. The OS may do zeroing when it allocates a block of memory to the application, but that wouldn't affect stack usage -- and the C code is allocating the structure on the stack. I presume Pascal is doing the same (since it allows recursion). Not seeing the declaration of "Data" means I can't be certain -- FreePascal may have keywords to force allocation on heap.. -- Dennis L Bieber -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/r4cqagp6uljj4n53p65c3j4tl6ds3078uj%404ax.com.
