hm2_eth: Fix invalid soft error

src/hal/drivers/mesa-hostmot2/hm2_eth.c

@@ -1023,10 +1023,11 @@ static int hm2_eth_send_queued_reads(hm2_lowlevel_io_t *this) {
     LBP16_INIT_PACKET4(*(lbp16_cmd_addr*)(board->read_packet_ptr), CMD_READ_COMM_CTRL_ADDR16(1), 0x8);
     board->read_packet_ptr += sizeof(lbp16_cmd_addr);
     board->queue_reads[board->queue_reads_count].buffer = &board->rxudpcount;
-    board->queue_reads[board->queue_reads_count].size = 2;
+    static_assert(sizeof(board->rxudpcount)==2, "board->rxudpcount must be one 16-bit word");
+    board->queue_reads[board->queue_reads_count].size = sizeof(board->rxudpcount);
     board->queue_reads[board->queue_reads_count].from = board->queue_buff_size;
     board->queue_reads_count++;
-    board->queue_buff_size += 2;
+    board->queue_buff_size += sizeof(board->rxudpcount);
 
     board->read_cnt++;
     // write then read back space 4 scratch register at 0010 to verify we got the right receive packet
@@ -1038,11 +1039,12 @@ static int hm2_eth_send_queued_reads(hm2_lowlevel_io_t *this) {
 
     LBP16_INIT_PACKET4(*(lbp16_cmd_addr*)(board->read_packet_ptr), CMD_READ_TIMER_ADDR16_INCR(4), 0x10);
     board->read_packet_ptr += sizeof(lbp16_cmd_addr);
-    board->queue_reads[board->queue_reads_count].buffer = &board->confirm_read_cnt;
-    board->queue_reads[board->queue_reads_count].size = 8;
+    board->queue_reads[board->queue_reads_count].buffer = &board->confirm_rw_cnt;
+    static_assert(sizeof(board->confirm_rw_cnt)==8, "board->confirm_rw_cnt must be two 32-bit words");
+    board->queue_reads[board->queue_reads_count].size = sizeof(board->confirm_rw_cnt);
     board->queue_reads[board->queue_reads_count].from = board->queue_buff_size;
     board->queue_reads_count++;
-    board->queue_buff_size += 8;
+    board->queue_buff_size += sizeof(board->confirm_rw_cnt);
 
     send = eth_socket_send(board->sockfd, (void*) &board->read_packet, board->read_packet_ptr - board->read_packet, 0);
     if(send < 0) {
@@ -1125,15 +1127,16 @@ static int hm2_eth_receive_queued_reads(hm2_lowlevel_io_t *this) {
         memcpy(board->queue_reads[i].buffer, &tmp_buffer[board->queue_reads[i].from], board->queue_reads[i].size);
     }
 
-    if(board->confirm_read_cnt != board->read_cnt && t2 < read_deadline)
+    if(board->confirm_rw_cnt.read_cnt != board->read_cnt && t2 < read_deadline)
         goto do_recv_packet;
 
     hm2_eth_reset_queued_reads(board);
 
     int result = 1;
-    // (this means that one in 2^32 lost writes will not be diagnosed,
-    // each time board->write_cnt overflows)
-    if(board->write_cnt && board->write_cnt != board->confirm_write_cnt) {
+    // The has_written_cnt is necessary because the thread cycle uses first
+    // read, then write. If we didn't check, then we'd be using uninitialized
+    // data read back from the board.
+    if(board->has_written_cnt && board->write_cnt != board->confirm_rw_cnt.write_cnt) {
         result = record_soft_error(board);
     } else {
         decrement_soft_error(board);
@@ -1229,6 +1232,7 @@ static int hm2_eth_send_queued_writes(hm2_lowlevel_io_t *this) {
     static_assert(sizeof(board->write_cnt)==4, "board->write_cnt must be 4 bytes");
     memcpy(board->write_packet_ptr, &board->write_cnt, sizeof(board->write_cnt));
     board->write_packet_ptr += sizeof(board->write_cnt);
+    board->has_written_cnt = 1;
 
     t0 = rtapi_get_time();
     send = eth_socket_send(board->sockfd, (void*) &board->write_packet, board->write_packet_ptr - board->write_packet, 0);
@@ -1815,6 +1819,7 @@ int rtapi_app_main(void) {
             continue;
         } 
         boards[i].read_cnt = boards[i].write_cnt = 0;
+        boards[i].has_written_cnt = 0;
         int *added = kvlist_lookup(&ifnames, ifptr);
         if(!added)
             goto error;

src/hal/drivers/mesa-hostmot2/hm2_eth.h

@@ -51,9 +51,17 @@ typedef struct {
     rtapi_u8 write_packet[1400];
     rtapi_u8 *write_packet_ptr;
     uint32_t read_cnt, write_cnt;
-    // these two fields must be kept together, they're read by a single
-    // read-request
-    uint32_t confirm_read_cnt, confirm_write_cnt;
+    struct {
+        // These two fields must be kept together. They are read by a single
+        // queued read-request and retrieve the above read_cnt and write_cnt
+        // added by hm2_eth_send_queued_reads() and hm2_eth_send_queued_writes().
+        // The values of the two should match or we know that the send/recv
+        // packets are out of sync.
+        uint32_t read_cnt;
+        uint32_t write_cnt;
+    } confirm_rw_cnt;
+    // Set when a queued write has set write_cnt in the board
+    int has_written_cnt;
 
     int comm_error_counter;
     uint16_t old_rxudpcount, rxudpcount;