While all the Canbus stuff is working very well, recording data on the integral SD Card is causing me a right headache.
Mounting the card works in SPI mode works (it's integral to the module; a Lolin D32 Pro), until the filesystem gets corrupted; see later, but I'm going round in circles trying to find a reliable way of writing data to it compounded by the fact that I have no control over the power to the ESP32 being cut; ignition switch turned off or the rider hitting a tyre wall! .
If I use fopen and fprintf, the file on the card doesn't seem to get updated (from a filesystem perspective) until I close it. Doing a stat() on the filename while it's open always shows that the file is zero length until it's closed (I'm guessing this is a 'feature' of FAT?). Even doing an fflush() after every fprintf or using setbuf(fp,0) doesn't have any effect.
Low level open and write suffer from the same problem although I'd hoped that O_SYNC would help:
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logfile_fd = open(logfile_name, O_WRONLY | O_CREAT | O_TRUNC | O_SYNC);
If I choose a value of N that I can live with then I still have the problem of the filesystem getting corrupted and refusing to mount when the ESP32 next boots. The ESP comes up with:
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Initializing SDCard... I (2391) gpio: GPIO| InputEn: 0| OutputEn: 1| OpenDrain: 0| Pullup: 0| Pulldown: 0| Intr:0 E (2441) sdmmc_cmd: sdmmc_card_init: send_if_cond (1) returned 0x108 I (2441) gpio: GPIO| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0 I (2441) gpio: GPIO| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0 I (2451) gpio: GPIO| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0 E (2461) App: Failed to initialize the card (ESP_ERR_INVALID_RESPONSE). Make sure SD card lines have pull-up resistors in place.
Once the card has got into this state, I have to remove it, stick in my Linux laptop and run a dosfsck on the partition. It normally finds the Free cluster summary is wrong and fixes it. I can then use the card in the ESP32 module again. Until I do this, the whole thing gets stuck at the above point with the need for physical intervention.
I would really like to retain the concept of a filesystem with files of data because I'm presenting and downloading them with a web server.
I surely can't be the only person trying to use an ESP32 as a data stream logger so can anyone help point me in the right direction?
Thanks in advance.