How do I write to an SD Card using SPI with DMA available for the PSoC 5LP (32-bit Cortex-M3) chip?
I currently have a DMA and SPI tx/rx pair working, but for a different purpose so if the actual transmission is not an issue, I just don't know how to interact with the SDcard.
The datasheet for the PSoC 5LP is here.
Basic Info:
I am using the DMA in simple mode and the DMA TD chain is setup for: 8 bit width, 4 Byte bursts auto complete the full TD (only needs initial HW request) Loop back to beginning of initial TD when done and wait for HW request
The SPI Master is initialized in a gui, I have it set using a 16Mhz clock, 8 bit tx/rx transfers with a 4 Byte tx/rx buffer. interrupts are set on rx FIFO full, connected to them is an rx DMA.
The pointers for the SDcard SPI rx/tx are SPIM_RX_PTR and SPIM_TX_PTR respectively. The DMA transfers to and from them. The Arrays that I am transferring from and to are SDcardout and SDcardin.
Having SPI communication will only get you the lowest command/block level access to the card; you will need a file system. SD cards come pre-formatted as FAT32, so a FAT file-system will provide the greatest comparability, is not the greatest reliability (corruption is likely if write is interrupted by power loss or reset for example). It also has the advantage of being relatively simple to implement and requires few resources.
There are several commercial and open-source FAT filesystems libraries available. I suggest that you look at ELM FatFs or ELM Petit FatFs both have permissive licences and are well documented. In each case you simply need to implement the disk I/O stubs to map them to your SPI driver. There are plenty of examples, documentation and application notes on the site to help you. You can start with an SPI SD implementation example for another target and adapt it to your driver (or adapt your driver perhaps). Other FAT filesystem libraries are broadly similar to this and require I/O layer implementation.
The diskio layer of ELM FatFs is not media specific, so you in fact need an additional MMC/SD layer between that and the SPI driver. It is unlikely that you will find an example for your specific target, but it is possible to work from examples for other targets since MMC/SD over SPI itself is not target specific, the hardware dependencies come only at the SPI level and the GPIO implementation for the card-detect and write-protect (optional) signals. There are several examples for various ARM targets here, a project for PSoC support here (apparently a work-in-progress at time of writing).