The 'pxi' sysmodule contains the following services:
Each of these services has up to 4 static IPC buffers of size 0x1000. When any of these service ports are sync:d, the IPC cmdbuf (TLS+0x80+) is sent over PXI to the ARM9.
Each PXI service can only have one session open for it at a time.
The communication protocol for normal PXI commands is documented below. The size of cmd_buf is calculated from the cmd_hdr. With newer FIRM the total size for command header + buffer must be at most 0x40 words, otherwise Process9 will panic.
The PXI protocol is bidirectional - both processors can host a PXI service for a given pxi_id. In practice, Process9 hosts all but one of the services (pxi_11 is hosted by pxi-module instead). Each pxi_id corresponds to a PXI command-handler(called from threads) which handles the actual command processing. With newer FIRM the pxi_id must be in a certain range.
There's a dedicated Process9 thread for receiving data from PXI(in newer FIRM this is the main-thread), once it finishes receiving a request it copies the cmd_buf into a buffer for the corresponding pxi_id then signals an event so that the cmd-handler thread can process it. Once a cmd-handler thread finishes processing a command, the thread itself then sends the response over PXI. This means that multiple commands for different pxiIDs can be be handled at the same time, even when one cmd-handler completely hangs/etc for example.
Process9 will execute svcBreak when it receives a PXI command with a pxi_id where another command with that same pxi_id is still being processed by the command-handler(this won't happen with commands sent by the ARM11 PXI-module, since it waits for the command reply before sending another command request for that same pxi_id).
PXI service "pxi_11"
|0x00010040||PublishToSubscriber - this exposes "srv:" notifications to the Process9-side using SRV:PublishToSubscriber (with flags=1), to allow sending card-insert notifications etc. directly to ARM11.|
A11->A9 (u32) pxi_id A11->A9 (u32) cmd_hdr A11->A9 (u32) cmd_buf
A9->A11 (u32) pxi_id A9->A11 (u32) cmd_hdr A9->A11 (u32) cmd_buf
0 = pxi_mc 1 = pxi_fs 2 = pxi_fs 3 = pxi_fs 4 = pxi_fs 5 = pxi_pm 6 = pxi_dev 7 = pxi_am 8 = pxi_ps 9 = pxi_11