Looks like the USART on F0 has the same problem, in 9 bit mode.
data is a uint16_t.
using this, as in usart_send();
USART_TDR(USART2) = data;
doesn't send the 9th bit. Instead it sends the LSB *again*, for reasons I'm
not sure of.
i.e.
send 0x100 -> transmits 0x000 (!)
send 0x001 -> transmits 0x101 (!)
send 0x101 -> transmits 0x101
however, if instead we use a 16 bit pointer, like this:
uint16_t *txp;
txp = (uint16_t *) &USART_TDR(USART2);
*txp = data;
it works as expected:
send 0x100 -> transmits 0x100
send 0x001 -> transmits 0x001
send 0x101 -> transmits 0x101
I can't figure out why though. USART_TDR() returns a MMIO32() which is a
uint32_t*. Can't reason why that would make it write the lowest byte twice,
instead of the two low bytes once..
any ideas..?
here is listing difference:
uint16_t *txp = (uint16_t *) &USART_TDR(usart);
*txp = data;
8000176: 8501 strh r1, [r0, #40] ; 0x28
USART_TDR(usart) = data;
8000176: 1c03 adds r3, r0, #0
8000178: b2c9 uxtb r1, r1
800017a: 3328 adds r3, #40 ; 0x28
800017c: 7019 strb r1, [r3, #0]
so with 16 bit pointer, it does a 16 bit write. without pointer it does an
8 (why??) bit one. which doesn't explain why bit 8 is mirroring bit 0.
On 16 August 2014 at 05:23, Karl P <ka...@tweak.net.au> wrote:
>
> See also https://github.com/libopencm3/libopencm3/issues/318
>
> This is a known issue, f3 has the same spi peripheral, and it regularly
> catches
> people, not just with libopencm3!
>
>
> On 08/16/2014 03:28 AM, Марко Краљевић wrote:
> > Today I started first work with STM3F0 series (F030, in 20 pin tssop.
> Should be
> > useful for small things, and very cheap).
> >
> > After setting SPI to 8 bit mode, a single uint8_t write to the SPI_DR
> will write
> > *two* bytes. (first your byte, and then a blank byte).
> >
> > Looking into this a bit, the SPI controller works somewhat differently
> on these,
> > and seems to ignore what it is set to if you write 16 bits to it. If
> that makes
> > sense.
> >
> > So, for reference, spi_send function:
> >
> > void spi_send
> > <
> https://libopencm3.github.io/docs/latest/stm32f1/html/group__spi__defines.html#ga1fcf7661af69bcf8999ae3f6d102fd8b
> >(uint32_t
> > spi, uint16_t data)
> > {
> > /* Wait for transfer finished. */
> > while (!(SPI_SR
> > <
> https://libopencm3.github.io/docs/latest/stm32f1/html/group__spi__defines.html#gae14de4e25f63b18a43dc0f20bdc4fe8e
> >(spi)
> > & SPI_SR_TXE
> > <
> https://libopencm3.github.io/docs/latest/stm32f1/html/group__spi__defines.html#ga5bd5d21816947fcb25ccae7d3bf8eb2c
> >));
> > /* Write data (8 or 16 bits, depending on DFF) into DR. */
> > SPI_DR
> > <
> https://libopencm3.github.io/docs/latest/stm32f1/html/group__spi__defines.html#ga9e95e2b653dfa3add622205d9cb0ddb5
> >(spi)
> > = data;
> > }
> >
> > Since data is a uint16_t, it writes 16 bits to the SPI_DR, which it
> interprets
> > as two 8bit transfers on a 'F0, apparently. Doesn't matter if you pass a
> uint8_t
> > to spi_send(); nor does the following work:
> >
> > uint8_t data = 0x55;
> > SPI_DR(spi) = data;
> >
> > as SPI_DR() must return a _16 bit_ pointer. I guess GCC then promotes
> your 8 bit
> > uint to a 16 bit one.
> >
> > The only thing that seems to work, is to have an 8 bit pointer to SPI_DR,
> > something like this:
> >
> > uint8_t *spi_8ptr;
> > spi_8ptr = (uint8_t *) &SPI_DR(spi);
> >
> > while (SPI_SR(spi) & SPI_SR_BSY);
> > *spi_8ptr = data;
> >
> > Though that will break 16bit transfers... Not sure what the best way to
> fix this
> > is? Anyone else work with SPI on F0? I guess there could be SPI_DR8();
> and
> > SPI_DR16(); but that's a little hokey... as all the higher level
> functions will
> > need to be either duplicated in 8/16 versions, or have a 8/16 bit
> argument
> > breaking everything.
> >
> > Anyway, that is all for now
> > mark
> >
> >
> >
> >
> ------------------------------------------------------------------------------
> >
> >
> >
> > _______________________________________________
> > libopencm3-devel mailing list
> > libopencm3-devel@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/libopencm3-devel
> >
>
>
> ------------------------------------------------------------------------------
> _______________________________________________
> libopencm3-devel mailing list
> libopencm3-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/libopencm3-devel
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