Mr Toad of Suttons Mill (by sarah)

A toad about 10cm in length was lerking on the step of the Mill so I cuaght it (gently in a well practiced have to relocate wildlife at Thirftwood in an ecologically sound manor) and then released it with the wiggly pets and camera. The photos arent as good as the shrew ones as a) it was dark so could not use the mode for lots of consecutive frames for animal and children photography and b) the thing hoped in the wrong direction - still the are passable photos 🙂

Now all I have to do is think up a sutiable storyline to go with the pics for the webcomic!

Good job I like wildlife living here 🙂

Weeding the Veggy Plot (by sarah)

Last night I decided that the courgettes had to be planted out - unfortunatly this ment I had to weed the veg plot first - so of I went. I got a bit carried away and weeded more area than I needed and went all faint and stuff but the veg plot is starting to look more respectable now and i think it counts as my aerobic excersise for the day 🙂

Unfortunatly the deer have desimated the peas so I just cleared the area they were in 🙁 But I also found several more potatoe plants I didnt know about 🙂

I've just taken 3 barrow loads of weeds to the compost heap! Full barrows too 🙂 I'm proud of myself 🙂

Of course the plot should never have been allowed to get in that state in the first place but as my health returns hopefully I'll be able to maintain things better 🙂

On the down side I've just found the magpies eating the butternuts - the little fruits were intermediate between ping pong ball and tennis ball and now they've been munched 🙁 - oh well I've already made ratatooey with courgettes from the compost heap (these are Babaras plants that she told us we could harvest from whilst shes away).

The Taming of the Shrew (by sarah)

People were round for the Jazz on the Common and Dads Birthday this weekend. This ment my perants were in the Mill - cries of theirs a baby mouse in the Mill went up and my brother David as always spent the next day trying to catch it - to no avail. I was taking up a coffee for mum when the cutest little shrew ran basically over my foot (well the edge of my sandle anyway). Without really thinking I put the cup of coffee down on the floor and picked up the shrew - it obviously tried to escape so I ended up holding it by the tail - expecting to be bitten at any moment but lo! It just wiggle flipped itself and scampered up my arm and round the back of my neck.

Dad cuaght it from its position on my shoulder and I went to get something to keep it in till the time of release 🙂 I heared dad giggling only to find when I got back that it had escaped and gone up his arm to the armpit and was tickling him!

We got it in a wine glass and dad showed it to the others whilst I grabed the camera and some wiggly pets. I put the wiggly pets down on the drive and set the camera up then did a quick check that the wine glass was going to be in shot the got dad to release the shrew 🙂

I'll try and blog the picks later 🙂

The silly creature wouldnt get out of the glass which was really sweet 🙂 It ran off and hide in the grass at the edge of the drive though me and dad knew where it was exactly! Later I checked and it had moved but less than 1/2 hr later Al reported that he had almost trodden on the thing trying to make its way back into the Mill so he hurridly made sure all doors were closed (hmmm... I suspect that little shrew is back in its cozy little nest somewhere in the Mill! Though how it avoids Tim and Besty is anyones guess!)

Missing Geology (by sarah)

Sigh - I'm keenly missing rocks!

I just want to be sitting at the microscope in the lab - desparing over what tyoe of feldspar happens to be at the cross wires, or at the museum photographing all those slides and finding obscure papers from the victorian era. I miss the smell of hydrochloric acid working on the sandstone.

I know I'm sounding sad but my MRes course have just told me I need to get a GP letter saying I am fit enough to continue - the GP already wasnt happy about the fact the course is in London. I just cant bare the thought of not being back in the lab for another two years :'(

I was so excited about my project - all those impactites waiting for my at the Mueseum, I should be just about finishing the thing now.

This really will balls up career plans and what not if I don't get that letter - sigh.

Apologies for the wading in self pitty.

CMOS transmission gates (by alaric)

As I mentioned before, I plan to implement CMOS transmission gates in my digital logic simulator.

However, while driving back from dropping Jean off at the nursery this morning, it struck me that they wouldn't be as trivial as I'd naively thought, for an obvious reason; if a change occurs on one data line, then the gate will cause a corresponding change to its driver on the other data line, after a small gate delay. However, the gate will also be bound as an output on that line, meaning that it will then be told of its own change when the scheduler performs it, so it'll end up making the same change on the output driver of the original input line, meaning it locks the line in that state; when any other drivers try to assert another logical state, there'll be a driver conflict.

Duh.

I see four possible solutions.

A third type of device < -> line connection

Right now, devices have a number of input pins and a number of output pins, each of which can be individually bound to a single line. Anything bidirectional has to be handled as a pair of pins, one input and one output, connected to the same line. For example, my SRAM device has data inputs and separate data outputs; and they can be joined to the same bus for a bidirectional interface, or wired independently. But perhaps I could introduce a third class of pin, bidirectional pins, which are handled specially; bidirectional pins would not be notified of changes to the line they cause. That way, a transmission gate could have two bidirectional pins, and whenever it receives a change on one, it copies the change to the other bidirectional pin. It'd keep track of which side was being driven and make sure the driver on that side was in the HI-Z state so as not to cause a collision.

Line bridging support

Perhaps I should make it possible to 'bridge' two lines. Pick one arbitrarily as the master, and the other as the slave, and inform them both of this fact. Then when the simulation loop has applied changes to one or more drivers of either line, the master is told to compute the line's new state; it asks the slave to compute the state of its drivers, then merges this with the state of its own drivers to deduce a shared state, which it then tells the slave to inform its connected devices of, before informing its own. The transmission gate would then work by, when the control input was asserted, bridging its two lines together, and unbridging them when the control input drops.

Not bothering

Perhaps I can get by without transmission gates. They're quite low level things, mainly useful in designing flip-flops and multiplexers, so I can probably just define higher-level devices that use them and be done with it. However, I did see high-level use for them in routing signals on bidirectional busses, which would otherwise have to be done with pairs of tristate buffers that listen to the read/write control signals on the bus and configure themselves appropriately, requiring extra logic, and being slower when implemented in silicon.

Using weak logic

As I sit writing this, I realise there's probably a simpler solution; I'll need to think longer to see if there are any showstopping gotchas. That's to use my weak logic system I designed, avoiding the need for any infrastructure changes at all. Under this system, the transmission gate would have (apart from the control input) two input pins and two output pins, designed such that each bidirectional interface is made by joining an input pin and an output pin to the same line. Any line state change notification from either input pin would be ignored if it matched the last state notified, to prevent changes bouncing back and forth between the two lines, but if not then the input line state would be weakly driven onto the opposite output pin. That way, if side A was in the 1 state, the transmission gate would output a weak 1 to side B; and if nothing else was driving side B (as should be the case in a bus), B would then end up in state 1. When the notification of B's resulting state change came back to the B input, it would be seen to be the same as the last state change sent through the gate, and ignored.

Likewise with state 0, and likewise if the sides are reversed.

It gets interesting if something on A drives a 1 and something on B drives a 0 (or vice versa), in which case, the transmission gate will be weakly driving a 1 onto B and a 0 onto A, which will have no effect and not raise an error, even though in a real circuit this would be shorting Vdd and Vss. So the transmission gate itself will need to notice that state and make an error message, I think.

Hmmm, that may be the correct solution... The only downside is that one cannot use weak logic for anything else on those lines, but I suspect one shouldn't be using weak logic around transmission gates anyway, due to the extra line resistance they cause.

Although I still think I'll introduce a weak notion of a bidirectional pin, even if just for neatness; as syntactic sugar, binding a bidirectional pin number N to a line will just bind input pin N and output pin N to the same line (input and output pins have separate numbering schemes).