46 lines
1.3 KiB
C
46 lines
1.3 KiB
C
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/** \file
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\brief SPI subsystem
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This is much simpler than Teacup's serial subsystem. No ring buffers, no
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"write string" functions. Usually using SPI directly is faster than fiddling
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with buffers. For example, reading or writing a byte can be done in as few
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as 20 clock cycles.
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Other than serial, SPI has to deal with multiple devices. Device selection
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happens before reading and writing, data exchange its self is the same for
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each device, then.
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*/
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#include "spi.h"
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#include "arduino.h"
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/** Initialise serial subsystem.
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Code copied from ATmega164/324/644/1284 data sheet, section 18.2, page 160,
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or moved here from mendel.c.
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*/
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void spi_init() {
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// Set SCK (clock) and MOSI line to output, ie. set USART in master mode.
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SET_OUTPUT(SCK);
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SET_OUTPUT(MOSI);
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SET_INPUT(MISO);
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// SS must be set as output to disconnect it from the SPI subsystem.
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// Too bad if something else tries to use this pin as digital input.
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// See ATmega164/324/644/1284 data sheet, section 18.3.2, page 162.
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// Not written there: this must apparently be done before setting the SPRC
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// register, else future R/W-operations may hang.
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SET_OUTPUT(SS);
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#ifdef SPI_2X
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SPSR = 0x01;
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#else
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SPSR = 0x00;
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#endif
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// This sets the whole SPRC register.
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spi_speed_100_400();
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}
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