This library file modifies an existing driver provided by TI and adds DMA functionality for sector transmissions.
The target architecture is ARM Cortex-M4, and was developed for TI's TM4C123 Launchpad using the CCS compiler.
Currently, there are a number of preprocessor functionality switches in the driver:
USE_FREERTOS- Use semaphore-based blocking for read and write operations.USE_DMA_TX- Use DMA-based write functions.USE_DMA_RX- Use DMA-based read functions.USE_SCATTERGATHER- Use scatter-gather (DMA subset functionality) for DMA-based operations.
It should be noted that for simplicity, the driver initializes the uDMAControlTable itself. If the application already does this, then the two lines:
static uint8_t ui8ControlTable[1024] __attribute__ ((aligned(1024)));ROM_uDMAControlBaseSet(ui8ControlTable);should be commented out in the driver code.
Finally, one interrupt handler SDCSSIIntHandler exists in the driver which is assigned to SSI0, and must be
reflected in the interrupt vector.
Micro-benchmark tests were performed with various modifications to the driver to determine how much
throughput can be achieved for MMC/SD. Unless otherwise noted, ARB_SIZE=4, BIT_WIDTH=8, and SSI_FRF_MOTO_MODE_0 are used.
SPI was set to 8 MHz and the transfer size was 8192 bytes.
Times are given in milliseconds (lower = better) and the corresponding ratios (higher = better) are given as normalized inverse to "no dma", which was the slowest of the set.
| mode | t_write (ms) | t_read (ms) | *_write | *_read |
|---|---|---|---|---|
| no dma | 47.12 | 47.40 | 1.00 | 1.00 |
| dma | 13.56 | 11.22 | 3.47 | 4.23 |
| dma-sg | 13.50 | 11.13 | 3.49 | 4.26 |
| no dma 16 | 33.47 | 31.33 | 1.41 | 1.51 |
| dma 16 | 21.09 | 18.83 | 2.23 | 2.52 |
| dma 16, arb8 | 21.17 | 18.83 | 2.23 | 2.52 |
| dma, moto3 | 12.36 | 9.67 | 3.81 | 4.90 |
- Modify DMA interrupt to re-initialize itself for multi-block transfers.
- Add sample project for testing.