From 11ebaaaa0b5981414779a085705abe4b699d8c50 Mon Sep 17 00:00:00 2001 From: Virgil Dupras Date: Sun, 8 Nov 2020 11:35:06 -0500 Subject: [PATCH] doc: add SPI relay instructions for the SMS --- doc/hw/z80/{ => sms}/code/smsps2ctl.fs | 0 doc/hw/z80/{ => sms}/img/ps2-to-sms.png | Bin doc/hw/z80/{sms.txt => sms/intro.txt} | 0 doc/hw/z80/{smsps2.txt => sms/ps2.txt} | 0 doc/hw/z80/sms/spi.txt | 41 ++++++++++++++++++++++++ 5 files changed, 41 insertions(+) rename doc/hw/z80/{ => sms}/code/smsps2ctl.fs (100%) rename doc/hw/z80/{ => sms}/img/ps2-to-sms.png (100%) rename doc/hw/z80/{sms.txt => sms/intro.txt} (100%) rename doc/hw/z80/{smsps2.txt => sms/ps2.txt} (100%) create mode 100644 doc/hw/z80/sms/spi.txt diff --git a/doc/hw/z80/code/smsps2ctl.fs b/doc/hw/z80/sms/code/smsps2ctl.fs similarity index 100% rename from doc/hw/z80/code/smsps2ctl.fs rename to doc/hw/z80/sms/code/smsps2ctl.fs diff --git a/doc/hw/z80/img/ps2-to-sms.png b/doc/hw/z80/sms/img/ps2-to-sms.png similarity index 100% rename from doc/hw/z80/img/ps2-to-sms.png rename to doc/hw/z80/sms/img/ps2-to-sms.png diff --git a/doc/hw/z80/sms.txt b/doc/hw/z80/sms/intro.txt similarity index 100% rename from doc/hw/z80/sms.txt rename to doc/hw/z80/sms/intro.txt diff --git a/doc/hw/z80/smsps2.txt b/doc/hw/z80/sms/ps2.txt similarity index 100% rename from doc/hw/z80/smsps2.txt rename to doc/hw/z80/sms/ps2.txt diff --git a/doc/hw/z80/sms/spi.txt b/doc/hw/z80/sms/spi.txt new file mode 100644 index 0000000..6276cb5 --- /dev/null +++ b/doc/hw/z80/sms/spi.txt @@ -0,0 +1,41 @@ +# Building a SPI relay for the SMS + +The I/O space on the SMS is, sadly, entirely taken. If you had +the idea of somehow plugging a SPI relay that is similar the one +on the RC2014, you can forget about it. Only A7, A6 and A0 are +considered by the 8 builtin peripherals on the SMS and trying to +do an IN or OUT to any address is going to end up conflicting +with one of them. + +What we can do to achieve SPI communication with the SMS is to +use the B controller port. It can already do bit banging. It's +slow, but it works. + +One problem we have, however, is that only 2 pins can be set as +output. We need 3. What I did, and it works with SD cards, is +to hard-wire CS to GND so that it's always turned on. The +downside of this is that if you go out-of-sync with the SPI +device, you have to physically disconnect it and reconnect it +to solve the sync problem. + +The advantage of using port B is that the connector is really +simple, you don't even need a schematic: + +* CLK to TH +* DI to TR +* DO to Up +* CS to GND + +Add pull-downs to CLK and DI to avoid messing up with your +device (it's always on, remember). + +# Building the binary + +The SPI driver is in B622, which depends on controller port +routines at B625-B626. A ready-to-use xcomp unit is at +arch/z80/sms/xcompsdc.fs. + +The SMS emulator has support for a SPI relay based on the B +controller port and can emulate a SD card plugged in it with the +"-c" argument. If it works in the emulator, it has good chances +of running on the real thing.