MB85RSxx FRAM bringup (#1757)

This branch adds an initial implementation of a driver for the Fujitsu
MB85xx series of ferroelectric RAM (FRAM) devices, as seen in Power
Shelf Controller rev C boards. The FRAM chip is a SPI device with a
fairly simple protocol, detailed in [the Fujitsu datasheet][1]. It also
has additional pins for toggling the write protection feature (which can
also be controlled over SPI) and a "hold" pin to maintain a read/write
transaction when CS is deasserted, but my driver doesn't currently use
those pins because we don't *really* need them.

I've also included a simple demo task which writes some data to a FRAM
device and checks whether it can be read back. Eventually, I'd like to
replace this with a more general-purpose "read the contents of the FRAM"
task that can be used for debugging purposes, but I've left it as is for
now in the interests of getting the driver implementation ready to
merge. I'll revisit this later.

[1]: https://www.mouser.com/datasheet/2/1113/MB85RS64T_DS501_00051_2v0_E-2329177.pdf

app/psc/base.toml

@@ -6,7 +6,7 @@ fwid = true
 
 [kernel]
 name = "psc"
-requires = {flash = 32768, ram = 5080}
+requires = {flash = 32868, ram = 5216}
 features = ["dump"]
 
 [caboose]

app/psc/rev-c-dev.toml

@@ -1,2 +1,10 @@
 name = "psc-c-dev"
 inherit = ["rev-c.toml", "dev.toml"]
+
+[tasks.framulator]
+name = "task-framulator"
+priority = 5
+start = true
+task-slots = [{spi_driver = "spi2_driver"}]
+stacksize = 2048
+notifications = ["hey-you"]

app/psc/rev-c.toml

@@ -2,3 +2,15 @@ name = "psc-c"
 board = "psc-c"
 
 inherit = "base.toml"
+
+# N.B. that the FRAM device is only present on rev-C PSC boards and later, so
+# this mux config isn't needed on earlier revisions.
+[config.spi.spi2.mux_options.port_b]
+outputs = [
+    {port = "B", pins = [13, 15], af = 5},
+]
+input = {port = "B", pin = 14, af = 5}
+
+[config.spi.spi2.devices.mb86rs64t]
+mux = "port_b"
+cs = [{port = "B", pin = 12}]

drv/mb85rsxx-fram/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "drv-mb85rsxx-fram"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+bitflags = { workspace = true }
+
+drv-spi-api = { path = "../spi-api" }
+counters = { path = "../../lib/counters" }
+
+[lints]
+workspace = true
+
+# This section is here to discourage RLS/rust-analyzer from doing test builds,
+# since test builds don't work for cross compilation.
+[lib]
+test = false
+doctest = false
+bench = false