Cannot write/read a byte from external Flash via SPI

RE: Cannot write/read a byte from external Flash via SPI

Turbo J — Thu, 13 Feb 2020 01:15:04 GMT

When manually operating CS, do not set it in the SPI config.

config.ss_pin    = NRF_DRV_SPI_PIN_NOT_USED;

RE: Cannot write/read a byte from external Flash via SPI

RO — Wed, 12 Feb 2020 16:10:23 GMT

I finally got a logic analyzer and found the the issue. The problem was with the CS line.

I am manually operating it in my code. But the nrf_xfer() function in nrf_drv_spi.c also operates on it once it detects a transfer is finished.

So it used to pull the CS line high between the SPI transfer function to send the Flash opcode & address and the SPI transfer function for the actual byte.

So I commented out the line which was pulling the CS pin high in the nrf_drv_spi.c

if (!p_cb->handler)
    {
        while (!nrf_spim_event_check(p_spim, NRF_SPIM_EVENT_END)){}
        if (p_cb->ss_pin != NRF_DRV_SPI_PIN_NOT_USED)
        {
            //nrf_gpio_pin_set(p_cb->ss_pin);        
        }
    }

Maybe a note can be mentioned in documentation regarding the operation of CS pin.

Thanks

RE: Cannot write/read a byte from external Flash via SPI

Turbo J — Fri, 07 Feb 2020 12:55:18 GMT

Dumb question: Which read command did you use, and did you try reading more than one byte?

RE: Cannot write/read a byte from external Flash via SPI

Edvin — Fri, 07 Feb 2020 12:24:28 GMT

[quote user="ro269"]The fact that I can read manufacturer and device ID over SPI, doesn't that prove that SPI connection has been correctly established?[/quote]

I agree. Again, I don't know what flash you are using. Did you check the datasheet to double check that you are sending the correct read commands? If you use an invalid command, it may be that the external flash doesn't give any replies, which probably will look like a lot of 0's on the SPI.

RE: Cannot write/read a byte from external Flash via SPI

RO — Thu, 06 Feb 2020 18:57:13 GMT

I don't have access to a logic analyzer yet. The fact that I can read manufacturer and device ID over SPI, doesn't that prove that SPI connection has been correctly established?
I tried with 500k frequency, and the config mode is correct too. For some reason I'm only reading zeros..

RE: Cannot write/read a byte from external Flash via SPI

Edvin — Thu, 06 Feb 2020 09:41:45 GMT

I don't know what external flash you use. You should check in the data sheet for the flash. Have you tried analyzing the SPI wires to see that the data that you are sending and receiving is actually being sent correctly? Have you tried lowering the SPI frequency? Perhaps the traces/wires are too long for 1M? Perhaps you are using the wrong config.mode?

RE: Cannot write/read a byte from external Flash via SPI

RO — Wed, 05 Feb 2020 17:02:20 GMT

I did the following:

write enable -> chip erase -> read (random address)

I still read 00. Shouldn't I read FF after a chip erase?

I added delays for each operation as per datasheet.

I can read status registers fine. Why am I not able read data in random address' correctly?

Thanks

RE: Cannot write/read a byte from external Flash via SPI

Edvin — Wed, 05 Feb 2020 11:29:34 GMT

Turbo J is correct. An erased byte is 0xFF, so if you are reading 0x00, that means that something else has already written to that address. Try to read it before you write to it.

So what you probably need to do is to find the SPI command to erase everything on the flash (or that specific flash page).

Best regards,

Edvin

RE: Cannot write/read a byte from external Flash via SPI

RO — Wed, 05 Feb 2020 01:02:28 GMT

Sorry I dont understand,

as wriiten in the code, I'm trying to write "0x23" to a specific memory location.

I want to read "0x23" back, am I doing something wrong?

Thanks

RE: Cannot write/read a byte from external Flash via SPI

Turbo J — Wed, 05 Feb 2020 00:48:16 GMT

[quote userid="25505" url="~/f/nordic-q-a/57395/cannot-write-read-a-byte-from-external-flash-via-spi"][/quote]

I am writing a byte to a specific address in Flash.

But when I try to read the memory location, On the debug window I only see "00".

You can only write "0" bits to flash.

Returning to "1" is the "erase" operation, which has its own command (and operates on a page or sector at a time).