Add an 8-bit CRC to each transmitted packet.

1 files changed, 56 insertions, 4 deletions

diff --git a/src/drivers/px4io/interface_serial.cpp b/src/drivers/px4io/interface_serial.cpp
index ffd852cf0..e688d672c 100644
--- a/src/drivers/px4io/interface_serial.cpp
+++ b/src/drivers/px4io/interface_serial.cpp
@@ -74,7 +74,7 @@ const unsigned	max_rw_regs = 32; // by agreement w/IO
 #pragma pack(push, 1)
 struct IOPacket {
 	uint8_t 	count_code;
-	uint8_t 	spare;
+	uint8_t 	crc;
 	uint8_t 	page;
 	uint8_t 	offset;
 	uint16_t	regs[max_rw_regs];
@@ -104,6 +104,9 @@ struct IOPacket {
 #define PKT_CODE(_p)	((_p).count_code & PKT_CODE_MASK)
 #define PKT_SIZE(_p)	((uint8_t *)&((_p).regs[PKT_COUNT(_p)]) - ((uint8_t *)&(_p)))
 
+static uint8_t		crc_packet(IOPacket &pkt);
+
+
 class PX4IO_serial : public PX4IO_interface
 {
 public:
@@ -338,7 +341,6 @@ PX4IO_serial::set_reg(uint8_t page, uint8_t offset, const uint16_t *values, unsi
 	sem_wait(&_bus_semaphore);
 
 	_dma_buffer.count_code = num_values | PKT_CODE_WRITE;
-	_dma_buffer.spare = 0;
 	_dma_buffer.page = page;
 	_dma_buffer.offset = offset;
 	memcpy((void *)&_dma_buffer.regs[0], (void *)values, (2 * num_values));
@@ -363,7 +365,6 @@ PX4IO_serial::get_reg(uint8_t page, uint8_t offset, uint16_t *values, unsigned n
 	sem_wait(&_bus_semaphore);
 
 	_dma_buffer.count_code = num_values | PKT_CODE_READ;
-	_dma_buffer.spare = 0;
 	_dma_buffer.page = page;
 	_dma_buffer.offset = offset;
 
@@ -417,6 +418,8 @@ PX4IO_serial::_wait_complete(bool expect_reply, unsigned tx_length)
 
 	/* start TX DMA - no callback if we also expect a reply */
 	/* DMA setup time ~3µs */
+	_dma_buffer.crc = 0;
+	_dma_buffer.crc = crc_packet(_dma_buffer);
 	_tx_dma_status = _dma_status_waiting;
 	stm32_dmasetup(
 		_tx_dma,
@@ -629,4 +632,53 @@ PX4IO_serial::_abort_dma()
 
 	_tx_dma_status = _dma_status_inactive;
 	_rx_dma_status = _dma_status_inactive;
-}
\ No newline at end of file
+}
+
+static const uint8_t crc8_tab[256] =
+{
+	0x00, 0x07, 0x0E, 0x09, 0x1C, 0x1B, 0x12, 0x15,
+	0x38, 0x3F, 0x36, 0x31, 0x24, 0x23, 0x2A, 0x2D,
+	0x70, 0x77, 0x7E, 0x79, 0x6C, 0x6B, 0x62, 0x65,
+	0x48, 0x4F, 0x46, 0x41, 0x54, 0x53, 0x5A, 0x5D,
+	0xE0, 0xE7, 0xEE, 0xE9, 0xFC, 0xFB, 0xF2, 0xF5,
+	0xD8, 0xDF, 0xD6, 0xD1, 0xC4, 0xC3, 0xCA, 0xCD,
+	0x90, 0x97, 0x9E, 0x99, 0x8C, 0x8B, 0x82, 0x85,
+	0xA8, 0xAF, 0xA6, 0xA1, 0xB4, 0xB3, 0xBA, 0xBD,
+	0xC7, 0xC0, 0xC9, 0xCE, 0xDB, 0xDC, 0xD5, 0xD2,
+	0xFF, 0xF8, 0xF1, 0xF6, 0xE3, 0xE4, 0xED, 0xEA,
+	0xB7, 0xB0, 0xB9, 0xBE, 0xAB, 0xAC, 0xA5, 0xA2,
+	0x8F, 0x88, 0x81, 0x86, 0x93, 0x94, 0x9D, 0x9A,
+	0x27, 0x20, 0x29, 0x2E, 0x3B, 0x3C, 0x35, 0x32,
+	0x1F, 0x18, 0x11, 0x16, 0x03, 0x04, 0x0D, 0x0A,
+	0x57, 0x50, 0x59, 0x5E, 0x4B, 0x4C, 0x45, 0x42,
+	0x6F, 0x68, 0x61, 0x66, 0x73, 0x74, 0x7D, 0x7A,
+	0x89, 0x8E, 0x87, 0x80, 0x95, 0x92, 0x9B, 0x9C,
+	0xB1, 0xB6, 0xBF, 0xB8, 0xAD, 0xAA, 0xA3, 0xA4,
+	0xF9, 0xFE, 0xF7, 0xF0, 0xE5, 0xE2, 0xEB, 0xEC,
+	0xC1, 0xC6, 0xCF, 0xC8, 0xDD, 0xDA, 0xD3, 0xD4,
+	0x69, 0x6E, 0x67, 0x60, 0x75, 0x72, 0x7B, 0x7C,
+	0x51, 0x56, 0x5F, 0x58, 0x4D, 0x4A, 0x43, 0x44,
+	0x19, 0x1E, 0x17, 0x10, 0x05, 0x02, 0x0B, 0x0C,
+	0x21, 0x26, 0x2F, 0x28, 0x3D, 0x3A, 0x33, 0x34,
+	0x4E, 0x49, 0x40, 0x47, 0x52, 0x55, 0x5C, 0x5B,
+	0x76, 0x71, 0x78, 0x7F, 0x6A, 0x6D, 0x64, 0x63,
+	0x3E, 0x39, 0x30, 0x37, 0x22, 0x25, 0x2C, 0x2B,
+	0x06, 0x01, 0x08, 0x0F, 0x1A, 0x1D, 0x14, 0x13,
+	0xAE, 0xA9, 0xA0, 0xA7, 0xB2, 0xB5, 0xBC, 0xBB,
+	0x96, 0x91, 0x98, 0x9F, 0x8A, 0x8D, 0x84, 0x83,
+	0xDE, 0xD9, 0xD0, 0xD7, 0xC2, 0xC5, 0xCC, 0xCB,
+	0xE6, 0xE1, 0xE8, 0xEF, 0xFA, 0xFD, 0xF4, 0xF3
+};
+
+static uint8_t
+crc_packet(IOPacket &pkt)
+{
+	uint8_t *end = (uint8_t *)(&pkt.regs[PKT_COUNT(pkt)]);
+	uint8_t *p = (uint8_t *)&pkt;
+	uint8_t c = 0;
+
+	while (p < end)
+		c = crc8_tab[c ^ *(p++)];
+
+	return c;
+}