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Altera_Forum's avatar
Altera_Forum
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13 years ago

SPI read example

Hello,

I need an example of the read transaction with the response. User Guide

"Embedded Peripherals IP" has only write example.

I tried the following transaction with no success: the packet format I pass:

0x7a, 0x7c, 0x0, 0x14, 0x0, 0x0, 0x4, 0x0, 0x0, 0x60, 0x7b, 0x8

That means read 4 bytes from address 0x00006008. But the response is always IDLE byte (0x4a), i.e. no data is returned.

2) Write transaction is successful and I get a proper response from the SPI, but after a Read transaction the Write always fails. :(

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    13 years ago

    Hi sercher,

    maybe I misunderstood but, are you trying to read from SPI without write on it?

    Remember that if the niosII is the master of the SPI transaction you have to write N bytes on the MOSI pin even if you wanna read N bytes. This because the slave is essentially a shift register and if you don't do this, it don't reply. Perhaps is this your problem?

    Try to use the alt_avalon_spi_command() function:

    this one first write X bytes and then read Y bytes (during this last operation it send 0 to the slave). I agree that if you have only to read, this is an oversized function, but it's a first step...
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    13 years ago

    Sorry, the problem was not linked with SPI, but with specific FPGA memory area. Other memory addresses work good for read.