/** * Copyright (c) 2023 Raspberry Pi (Trading) Ltd. * * SPDX-License-Identifier: BSD-3-Clause */ // Use the DMA engine's 'sniff' capability to calculate a CRC32 on data in a buffer. // Note: This does NOT do an actual data copy, it 'transfers' all the data to a single // dummy destination byte so as to be able to crawl over the input data using a 'DMA'. // If a data copy *with* a CRC32 sniff is required, the start address of the suitably sized // destination buffer must be supplied and the 'write_increment' set to true (see below). #include <stdio.h> #include <string.h> #include "pico/stdlib.h" #include "hardware/dma.h" #define CRC32_INIT ((uint32_t)-1l) #define DATA_TO_CHECK_LEN 9 #define CRC32_LEN 4 #define TOTAL_LEN (DATA_TO_CHECK_LEN + CRC32_LEN) // commonly used crc test data and also space for the crc value static uint8_t src[TOTAL_LEN] = { 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x00, 0x00, 0x00, 0x00 }; static uint8_t dummy_dst[1]; // This uses a standard polynomial with the alternate 'reversed' shift direction. // It is possible to use a non-reversed algorithm here but the DMA sniff set-up // below would need to be modified to remain consistent and allow the check to pass. static uint32_t soft_crc32_block(uint32_t crc, uint8_t *bytp, uint32_t length) { while(length--) { uint32_t byte32 = (uint32_t)*bytp++; for (uint8_t bit = 8; bit; bit--, byte32 >>= 1) { crc = (crc >> 1) ^ (((crc ^ byte32) & 1ul) ? 0xEDB88320ul : 0ul); } } return crc; } int main() { uint32_t crc_res; stdio_init_all(); // calculate and append the crc crc_res = soft_crc32_block(CRC32_INIT, src, DATA_TO_CHECK_LEN); *((uint32_t *)&src[DATA_TO_CHECK_LEN]) = crc_res; printf("Buffer to DMA: "); for (int i = 0; i < TOTAL_LEN; i++) { printf("0x%02x ", src[i]); } printf("\n"); // UNcomment the next line to deliberately corrupt the buffer //src[0]++; // modify any byte, in any way, to break the CRC32 check // Get a free channel, panic() if there are none int chan = dma_claim_unused_channel(true); // 8 bit transfers. The read address increments after each transfer but // the write address remains unchanged pointing to the dummy destination. // No DREQ is selected, so the DMA transfers as fast as it can. dma_channel_config c = dma_channel_get_default_config(chan); channel_config_set_transfer_data_size(&c, DMA_SIZE_8); channel_config_set_read_increment(&c, true); channel_config_set_write_increment(&c, false); // (bit-reverse) CRC32 specific sniff set-up channel_config_set_sniff_enable(&c, true); dma_sniffer_set_data_accumulator(CRC32_INIT); dma_sniffer_set_output_reverse_enabled(true); dma_sniffer_enable(chan, DMA_SNIFF_CTRL_CALC_VALUE_CRC32R, true); dma_channel_configure( chan, // Channel to be configured &c, // The configuration we just created dummy_dst, // The (unchanging) write address src, // The initial read address TOTAL_LEN, // Total number of transfers inc. appended crc; each is 1 byte true // Start immediately. ); // We could choose to go and do something else whilst the DMA is doing its // thing. In this case the processor has nothing else to do, so we just // wait for the DMA to finish. dma_channel_wait_for_finish_blocking(chan); uint32_t sniffed_crc = dma_sniffer_get_data_accumulator(); printf("Completed DMA sniff of %d byte buffer, DMA sniff accumulator value: 0x%x\n", TOTAL_LEN, sniffed_crc); if (0ul == sniffed_crc) { printf("CRC32 check is good\n"); } else { printf("ERROR - CRC32 check FAILED!\n"); } }

This firmware image was imported from the pico-examples repository. 


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