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Support cards such as natsemi which treat the data as little-endian

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(i.e. LSB transmitted first on the wire), even though SPI commands and
addresses always have to be big-endian.
This commit is contained in:
Michael Brown 2007-07-01 15:22:12 +01:00
parent 3bf5eb49d0
commit 95cb7aaacf
2 changed files with 39 additions and 17 deletions
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41
src/drivers/bitbash/spi_bit.c
View File

@ -73,6 +73,7 @@ static void spi_bit_set_slave_select ( struct spi_bit_basher *spibit,
* @v data_out TX data buffer (or NULL)
* @v data_in RX data buffer (or NULL)
* @v len Length of transfer (in @b bits)
* @v endianness Endianness of this data transfer
*
* This issues @c len clock cycles on the SPI bus, shifting out data
* from the @c data_out buffer to the MOSI line and shifting in data
@ -82,31 +83,34 @@ static void spi_bit_set_slave_select ( struct spi_bit_basher *spibit,
*/
static void spi_bit_transfer ( struct spi_bit_basher *spibit,
const void *data_out, void *data_in,
unsigned int len ) {
unsigned int len, int endianness ) {
struct spi_bus *bus = &spibit->bus;
struct bit_basher *basher = &spibit->basher;
unsigned int sclk = ( ( bus->mode & SPI_MODE_CPOL ) ? 1 : 0 );
unsigned int cpha = ( ( bus->mode & SPI_MODE_CPHA ) ? 1 : 0 );
unsigned int offset;
unsigned int mask;
unsigned int bit_offset;
unsigned int byte_offset;
unsigned int byte_mask;
unsigned int bit;
int step;
unsigned int step;
DBG ( "Transferring %d bits in mode %x\n", len, bus->mode );
for ( step = ( ( len * 2 ) - 1 ) ; step >= 0 ; step-- ) {
/* Calculate byte offset within data and bit mask */
offset = ( step / 16 );
mask = ( 1 << ( ( step % 16 ) / 2 ) );
for ( step = 0 ; step < ( len * 2 ) ; step++ ) {
/* Calculate byte offset and byte mask */
bit_offset = ( ( endianness == SPI_BIT_BIG_ENDIAN ) ?
( len - ( step / 2 ) - 1 ) : ( step / 2 ) );
byte_offset = ( bit_offset / 8 );
byte_mask = ( 1 << ( bit_offset % 8 ) );
/* Shift data in or out */
if ( sclk == cpha ) {
const uint8_t *byte;
/* Shift data out */
if ( data_out ) {
byte = ( data_out + offset );
bit = ( *byte & mask );
byte = ( data_out + byte_offset );
bit = ( *byte & byte_mask );
} else {
bit = 0;
}
@ -117,9 +121,9 @@ static void spi_bit_transfer ( struct spi_bit_basher *spibit,
/* Shift data in */
bit = read_bit ( basher, SPI_BIT_MISO );
if ( data_in ) {
byte = ( data_in + offset );
*byte &= ~mask;
*byte |= ( bit & mask );
byte = ( data_in + byte_offset );
*byte &= ~byte_mask;
*byte |= ( bit & byte_mask );
}
}
@ -155,17 +159,20 @@ static int spi_bit_rw ( struct spi_bus *bus, struct spi_device *device,
/* Transmit command */
assert ( device->command_len <= ( 8 * sizeof ( tmp ) ) );
tmp = cpu_to_le32 ( command );
spi_bit_transfer ( spibit, &tmp, NULL, device->command_len );
spi_bit_transfer ( spibit, &tmp, NULL, device->command_len,
SPI_BIT_BIG_ENDIAN );
/* Transmit address, if present */
if ( address >= 0 ) {
assert ( device->address_len <= ( 8 * sizeof ( tmp ) ) );
tmp = cpu_to_le32 ( address );
spi_bit_transfer ( spibit, &tmp, NULL, device->address_len );
spi_bit_transfer ( spibit, &tmp, NULL, device->address_len,
SPI_BIT_BIG_ENDIAN );
}
/* Transmit/receive data */
spi_bit_transfer ( spibit, data_out, data_in, ( len * 8 ) );
spi_bit_transfer ( spibit, data_out, data_in, ( len * 8 ),
spibit->endianness );
/* Deassert chip select on specified slave */
spi_bit_set_slave_select ( spibit, device->slave, DESELECT_SLAVE );

15
src/include/gpxe/spi_bit.h
View File

@ -16,6 +16,15 @@ struct spi_bit_basher {
struct spi_bus bus;
/** Bit-bashing interface */
struct bit_basher basher;
/** Endianness of data
*
* SPI commands and addresses are always big-endian (i.e. MSB
* transmitted first on the wire), but some cards
* (e.g. natsemi) choose to regard the data stored in the
* EEPROM as little-endian (i.e. LSB transmitted first on the
* wire).
*/
int endianness;
};
/** Bit indices used for SPI bit-bashing interface */
@ -41,6 +50,12 @@ enum {
/** Delay between SCLK transitions */
#define SPI_BIT_UDELAY 1
/** SPI bit basher treats data as big-endian */
#define SPI_BIT_BIG_ENDIAN 0
/** SPI bit basher treats data as little-endian */
#define SPI_BIT_LITTLE_ENDIAN 1
extern void init_spi_bit_basher ( struct spi_bit_basher *spibit );
#endif /* _GPXE_SPI_BIT_H */