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Altera_Forum
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15 years ago

MMC SPI Core with FIFO

Hi, The MMC SD card access using Altera's normal spi IP core is quite slow, because the core has only one byte Tx and Rx buffer, so the driver can send and receive only one byte at once. The s...
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Altera_Forum
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15 years ago

Hi,

I forgot to mention that the signal 'TRDY' is treated as the threshold of 'tx' FIFO buffer. So we need special attentions around 'TRDY', for example, 


//  assign readyfordata = TRDY; 
  assign readyfordata = ~tx_fifo_full; 
//  assign write_tx_holding = data_wr_strobe & TRDY; 
  assign write_tx_holding = data_wr_strobe; 
//          if (data_wr_strobe & ~TRDY) 
          if (data_wr_strobe & tx_fifo_full) 
              // You wrote when I wasn't ready. 
              TOE <= 1;
etc.

And there was a bug in the driver 'altspi.c'. 

# ifdef MMC_SPI_FIFO
    if (hw->mode == SPI_FIFO) { 
        if (hw->txd_count < hw->len) {
            if (spsta & ALTERA_SPI_STATUS_TRDY_MSK) {        
                txd_limit = ((hw->len - hw->txd_count) > MMC_SPI_FIFO_DEPTH / 2) ? hw->txd_count + MMC_SPI_FIFO_DEPTH / 2 : hw->len;  
                for (count = hw->txd_count; count < txd_limit; count++, hw->txd_count++)
                    writel(hw_txbyte(hw, count), hw->base + ALTERA_SPI_TXDATA);
            } else {
                count = hw->txd_count++;   // <--- Here!
                writel(hw_txbyte(hw, count), hw->base + ALTERA_SPI_TXDATA);
            }
        } else {
            if (hw->count == hw->len) {
                complete(&hw->done);
            }
        }
    } else {
Kazu