Root/drivers/spi/spi-bitbang-txrx.h

1/*
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:
4 *
5 * - GPIO/parport bitbangers. Provide chipselect() and txrx_word[](),
6 * expanding the per-word routines from the inline templates below.
7 *
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.
11 *
12 * Some hardware works well with requests at spi_transfer scope:
13 *
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.
17 */
18
19/*
20 * The code that knows what GPIO pins do what should have declared four
21 * functions, ideally as inlines, before including this header:
22 *
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);
27 *
28 * setsck()'s is_on parameter is a zero/nonzero boolean.
29 *
30 * setmosi()'s is_on parameter is a zero/nonzero boolean.
31 *
32 * getmiso() is required to return 0 or 1 only. Any other value is invalid
33 * and will result in improper operation.
34 *
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).
38 *
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.
43 */
44
45static inline u32
46bitbang_txrx_be_cpha0(struct spi_device *spi,
47        unsigned nsecs, unsigned cpol, unsigned flags,
48        u32 word, u8 bits)
49{
50    /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
51
52    /* clock starts at inactive polarity */
53    for (word <<= (32 - bits); likely(bits); bits--) {
54
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) */
59
60        setsck(spi, !cpol);
61        spidelay(nsecs);
62
63        /* sample MSB (from slave) on leading edge */
64        word <<= 1;
65        if ((flags & SPI_MASTER_NO_RX) == 0)
66            word |= getmiso(spi);
67        setsck(spi, cpol);
68    }
69    return word;
70}
71
72static inline u32
73bitbang_txrx_be_cpha1(struct spi_device *spi,
74        unsigned nsecs, unsigned cpol, unsigned flags,
75        u32 word, u8 bits)
76{
77    /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
78
79    /* clock starts at inactive polarity */
80    for (word <<= (32 - bits); likely(bits); bits--) {
81
82        /* setup MSB (to slave) on leading edge */
83        setsck(spi, !cpol);
84        if ((flags & SPI_MASTER_NO_TX) == 0)
85            setmosi(spi, word & (1 << 31));
86        spidelay(nsecs); /* T(setup) */
87
88        setsck(spi, cpol);
89        spidelay(nsecs);
90
91        /* sample MSB (from slave) on trailing edge */
92        word <<= 1;
93        if ((flags & SPI_MASTER_NO_RX) == 0)
94            word |= getmiso(spi);
95    }
96    return word;
97}
98

Archive Download this file

Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master

Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9



interactive