lots of design choices Brian REXCPM is SRAM not Flash. SDcards can't be used as system memory. convenient connection to M100 is a big factor. power consumption is another. a project I am willing to take on is another ;)
Anyhow I think there are a couple of scenarios 1) user has a PC with an FTDI based USB serial port. That supports 76800 and the normal M100 RS-232 port 2) user has a PC with RS-232. In this case standard port can go 38400 max. In this case 57600 is a bit faster. The original motivation for the BCR ttl interface was for video; that still seems like the right thing, and then using an FTDI based serial port for the fastest solution @76800. On Sun, Apr 26, 2020 at 12:21 AM Brian K. White <b.kenyo...@gmail.com> wrote: > On 4/25/20 10:25 PM, Stephen Adolph wrote: > > Still playing around with the BCR TTL serial port. > > ...yes it has it's limitations... half duplex, no flow control, > bit-banged > > > > ..but it is fast! Today I was able to get 32kB transferred in 7 > > seconds. That's pretty close to 100% utilization on the 57600 baud line. > > > > I think that is a new M100 record. It might need independent > verification! > > > > (why? to reduce time for CP/M disk backups. 4MB will take a 1/2 hour > > with this approach, or more than an hour at 19200 baud.) > > Thinking high level, ignoring for the moment that you've already gone a > long way down a certain road and the work is done etc... > > By the time you have to go that far, to get only that far, why keep > bothering with the bcr port instead of just using the system bus? > 1/2 hour is still too long. > > You've got a custom pcbs filling both the optrom and system bus sockets > already anyway, and both sockets are on the bus, so you might as well > use the system bus pcb for a better uart or off the shelf module, and a > connector. > > Or make the 4MB removable via microsd instead of soldered on flash? > Again if there is no room for that on the optrom pcb, couldn't that go > on the system bus pcb? The two should be able to talk to each other > through the bus itself, since they're both on it. > > They make very small already self-contained arduino microcontrollers > coupled with an sd card slot, where you could talk to it directly via > ttl or i2c or SPI on just a few wires totally aside from the bus and it > all would fit in the optrom compartment. > > https://www.amazon.com/dp/B07XDTGPCX > > I have a couple of those and took a couple pics to show where it could > fit in the cavity. If it was simply double-side taped or glued right to > the back of the system bus pcb, it might might just fit under the stock > door cover if the system bus pcb sits very close to the socket, or, even > if it's too tall, it definitely fits next to the optorm socket. > > https://photos.app.goo.gl/3sMyAkeebKYJALwz5 > > > Actually now that I think about it, you could leave the existing 4MB > flash as it is and just add the openlog as the backup/restore > destination instead of another host. It's the same serial connection > you're already set up to use. They already have firmware that does > nothing but the job of storing and retrieving from serial to sdcard. > > https://learn.sparkfun.com/tutorials/openlog-hookup-guide/all > > -- > bkw >
