2 * Mix this utility code with some glue code to get one of several types of
3 * simple SPI master driver. Two do polled word-at-a-time I/O:
5 * - GPIO/parport bitbangers. Provide chipselect() and txrx_word[](),
6 * expanding the per-word routines from the inline templates below.
8 * - Drivers for controllers resembling bare shift registers. Provide
9 * chipselect() and txrx_word[](), with custom setup()/cleanup() methods
10 * that use your controller's clock and chipselect registers.
12 * Some hardware works well with requests at spi_transfer scope:
14 * - Drivers leveraging smarter hardware, with fifos or DMA; or for half
15 * duplex (MicroWire) controllers. Provide chipselect() and txrx_bufs(),
16 * and custom setup()/cleanup() methods.
20 * The code that knows what GPIO pins do what should have declared four
21 * functions, ideally as inlines, before including this header:
23 * void setsck(struct spi_device *, int is_on);
24 * void setmosi(struct spi_device *, int is_on);
25 * int getmiso(struct spi_device *);
26 * void spidelay(unsigned);
28 * setsck()'s is_on parameter is a zero/nonzero boolean.
30 * setmosi()'s is_on parameter is a zero/nonzero boolean.
32 * getmiso() is required to return 0 or 1 only. Any other value is invalid
33 * and will result in improper operation.
35 * A non-inlined routine would call bitbang_txrx_*() routines. The
36 * main loop could easily compile down to a handful of instructions,
37 * especially if the delay is a NOP (to run at peak speed).
39 * Since this is software, the timings may not be exactly what your board's
40 * chips need ... there may be several reasons you'd need to tweak timings
41 * in these routines, not just make to make it faster or slower to match a
42 * particular CPU clock rate.
46 bitbang_txrx_be_cpha0(struct spi_device
*spi
,
47 unsigned nsecs
, unsigned cpol
, unsigned flags
,
50 /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
52 /* clock starts at inactive polarity */
53 for (word
<<= (32 - bits
); likely(bits
); bits
--) {
55 /* setup MSB (to slave) on trailing edge */
56 if ((flags
& SPI_MASTER_NO_TX
) == 0)
57 setmosi(spi
, word
& (1 << 31));
58 spidelay(nsecs
); /* T(setup) */
63 /* sample MSB (from slave) on leading edge */
65 if ((flags
& SPI_MASTER_NO_RX
) == 0)
73 bitbang_txrx_be_cpha1(struct spi_device
*spi
,
74 unsigned nsecs
, unsigned cpol
, unsigned flags
,
77 /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
79 /* clock starts at inactive polarity */
80 for (word
<<= (32 - bits
); likely(bits
); bits
--) {
82 /* setup MSB (to slave) on leading edge */
84 if ((flags
& SPI_MASTER_NO_TX
) == 0)
85 setmosi(spi
, word
& (1 << 31));
86 spidelay(nsecs
); /* T(setup) */
91 /* sample MSB (from slave) on trailing edge */
93 if ((flags
& SPI_MASTER_NO_RX
) == 0)
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