diff options
Diffstat (limited to 'host/lib/usrp/x300/x300_io_impl.cpp')
| -rw-r--r-- | host/lib/usrp/x300/x300_io_impl.cpp | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/host/lib/usrp/x300/x300_io_impl.cpp b/host/lib/usrp/x300/x300_io_impl.cpp index 04042049d..334ae8168 100644 --- a/host/lib/usrp/x300/x300_io_impl.cpp +++ b/host/lib/usrp/x300/x300_io_impl.cpp @@ -244,6 +244,12 @@ struct x300_tx_fc_guts_t #define X300_ASYNC_EVENT_CODE_FLOW_CTRL 0 +/*! + * If the return value of this function is F, the last tx'd packet + * has index N and the last ack'd packet has index M, the amount of + * FC credit we have is C = F + M - N (i.e. we can send C more packets + * before getting another ack). + */ static size_t get_tx_flow_control_window(size_t frame_size, const device_addr_t& tx_args) { double hw_buff_size = tx_args.cast<double>("send_buff_size", X300_TX_HW_BUFF_SIZE); @@ -318,9 +324,12 @@ static managed_send_buffer::sptr get_tx_buff_with_flowctrl( ){ while (true) { + // delta is the amount of FC credit we've used up const size_t delta = (guts->last_seq_out & 0xfff) - (guts->last_seq_ack & 0xfff); - if ((delta & 0xfff) <= fc_pkt_window) break; + // If we want to send another packet, we must have FC credit left + if ((delta & 0xfff) < fc_pkt_window) break; + // If credit is all used up, we check seq_queue for more. const bool ok = guts->seq_queue.pop_with_timed_wait(guts->last_seq_ack, timeout); if (not ok) return managed_send_buffer::sptr(); //timeout waiting for flow control } |