Re: [Discuss-gnuradio] setting fields in the USB packet

[Eric Blossom]

On Fri, Apr 06, 2007 at 12:17:40PM -0400, George Nychis wrote:
> actually some of this is changing to pmt related stuff, now that I'm 
> reading more in to the pmt class.  I'm going to check in some high level 
> stuff in my branch tonight probably that you can look over instead.

George, I don't think any pmt stuff should enter into these functions.
This shouldn't take that long to implement.  Here's 75% of the answer:



#include <usrp_bytesex.h>

static const int USB_PKT_SIZE = 512;     // bytes

class usrp_inband_usb_packet {
  //
  // keep raw packet in USRP-endian order
  //
  uint32_t        d_word0;
  uint32_t        d_timestamp;
  unsigned char   d_payload[USB_PKT_SIZE-2*sizeof(uint32_t)];

public:

  enum flags {
    FL_OVERRUN        = 0x80000000,
    FL_UNDERRUN       = 0x40000000,
    FL_DROPPED        = 0x20000000,
    FL_END_OF_BURST   = 0x10000000,
    FL_START_OF_BURST = 0x08000000,

    FL_ALL_FLAGS      = 0xf8000000
  };

  ...

  static const int CHAN_MASK = 0x1f;
  static const int CHAN_SHIFT = 16;

  ...


public:
  
  void set_timestamp(uint32_t timestamp){
    d_timestamp = host_to_usrp_u32(timestamp);
  }

  uint32_t timestamp() const {
    return usrp_to_host_u32(d_timestamp);
  }

  void set_header(int flags, int chan, int tag, int payload_len){
    uint32_t word0 =  ((flags & FL_ALL_FLAGS)
                       | ((chan & CHAN_MASK) << CHAN_SHIFT)
                       | ((tag & TAG_MASK) << TAG_SHIFT)
                       | ((payload_len & PAYLOAD_LEN_MASK) << 
PAYLOAD_LEN_SHIFT));
    d_word0 = host_to_usrp_u32(word0);
  }

  int flags() const {
    return usrp_to_host_u32(d_word0) & FL_ALL_FLAGS;
  }

  int rssi() const {
    ...  
  }

  int chan() const {
    uint32_t word0 = usrp_to_host_u32(d_word0);
    return (word0 >> CHAN_SHIFT) & CHAN_MASK;
  }

  int tag() const {
    ...
  }

  int payload_len() const {
    ...
  }

  ...

  //! return pointer to byte 0 of payload area
  unsigned char *payload(){ return d_payload; }

};



> - George
> 
> 
> George Nychis wrote:
> >Heyo,
> >
> >Eric, I think you started to mention something about this last night.  
> >But do we want a separate method for setting each field in the USB 
> >packet?  There are several fields that we won't ever need to set on our 
> >end, only need to read. For instance, the dropped packets field.
> >
> >So heres what i'm thinking:
> >
> >// Create the payload
> >//   'packet_ptr' is a pointer to a USB packet in memory
> >//   'samples'    is a vector of unsigned char
> >//
> >//   the payload can be inferred from the samples and inserted in to the 
> >packet
> >//
> >//   the method should also pad the payload
> >
> >usb_set_payload(packet_ptr, samples)
> >
> >
> >// Set the timestamp
> >//
> >// 'packet_ptr' is a pointer to a USB packet in memory
> >// 'timestamp' is a 32 bit int
> >
> >usb_set_timestamp(packet_ptr, timestamp)
> >
> >
> >// Set the channel
> >//
> >// 'packet_ptr' is a pointer to a USB packet in memory
> >// 'channel'    is an integer
> >//
> >// Should this also error check on the channel number? (5-bit limit)
> >
> >usb_set_channel(packet_ptr, channel)
> >
> >
> >// Set the start of burst flag
> >//
> >// 'packet_ptr' is a pointer to a USB packet in memory
> >//
> >// This just needs to flip a bit
> >
> >usb_set_start_of_burst(packet_ptr)
> >
> >
> >// Set the end of burst flag
> >//
> >// 'packet_ptr' is a pointer to a USB packet in memory
> >//
> >// This just needs to flip a bit
> >
> >usb_set_end_of_burst(packet_ptr)
> >
> >
> >Discussion:
> >-----------
> >
> >Do we need methods to unset burst flags?  I don't see a need for them.
> >
> >Should we have a method to zero out the packet?  Or are we just going to 
> >just use low level memory clearing methods?
> >
> >- George