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下载了 spiflash_writer_dsp 这个程序,运行正确,仔细分析了代码,有个疑惑的地方:
spi_xfer这个函数: int spi_xfer(struct spi_slave *slave, unsigned int bitlen, const void *dout, void *din, unsigned long flags) [ struct davinci_spi_slave *ds = to_davinci_spi(slave); unsigned int len; int i; const Uint8 *txp = dout; Uint8 *rxp = din; if (bitlen == 0) /* Finish any previously submitted transfers */ goto out; /* * It's not clear how non-8-bit-aligned transfers are supposed to be * represented as a stream of bytes...this is a limitation of * the current SPI interface - here we terminate on receiving such a * transfer request. */ if (bitlen % 8) [ /* Errors always terminate an ongoing transfer */ flags |= SPI_XFER_END; goto out; ] len = bitlen / 8; /* do an empty read to clear the current contents */ SPI_SPIBUF; /* keep writing and reading 1 byte until done */ for (i = 0; i < len; i++) [ /* wait till TXFULL is asserted */ while( SPI_SPIBUF & 0x20000000 ); /* write the data */ data1_reg_val &= ~0xFFFF; if(txp) [ data1_reg_val |= *txp & 0xFF; txp++; ] /* write to DAT1 is required to keep the serial transfer going */ /* we just terminate when we reach the end */ if((i == (len -1)) && (flags & SPI_XFER_END)) [ SPI_SPIDAT1 = data1_reg_val & ~(1 << 28); ] else [ SPI_SPIDAT1 = data1_reg_val; ] /* read the data - wait for data availability */ while ( SPI_SPIBUF & ( 0x80000000 ) ); if(rxp) [ *rxp = SPI_SPIBUF & 0xFF; rxp++; ] else [ SPI_SPIBUF; ] ] return 0; out: if (flags & SPI_XFER_END) [ SPI_SPIDAT1 = data1_reg_val & ~(1 << 28); ] return 0; ] 有一个语句: /* read the data - wait for data availability */ while ( SPI_SPIBUF & ( 0x80000000 ) ); 为什么需要这个?winbond SPI有些命令,比如 0x06,写允许命令,并不返回数据,岂不是一直等待! 请 TI 专家解释解释。 |
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