docs: Document changes

docs/tg/xilinx.md

@@ -130,7 +130,7 @@ The second command only ensures correctness of the partition layout; it moves th
 
 Insert your SD card and reset into boot mode 1. You should see a `Hello World!` UART output.
 
-### Boot from onboard flash (`vcu128` only)
+### Boot from onboard flash
 
 Build a GPT disk image for your desired binary as explained above, then flash it to your board's flash. For `helloworld`:
 
@@ -179,4 +179,5 @@ Flash your image to an SD card or SPI flash as described in the preceding sectio
 (    P      )
 (           ))))))))))
 ```
+
 You should then boot through OpenSBI, U-Boot, and Linux until you are dropped into a shell.

docs/um/sw.md

@@ -51,6 +51,8 @@ The boot ROM supports four builtin boot modes chosen from by the `boot_mode_i` p
 | `0b10`              | EEPROM (24FC1025)     | I2C                        |
 
 
+Should a program invoked by the boot ROM return, the boot ROM will attempt to yield control to an external debugger if present, such as GDB, using the `ebreak` instruction.
+
 #### Passive Preload
 
 The *passive preload* boot mode expects code to be preloaded to an executable location and an entry point to be written to `scratch[1:0]`. After preloading, execution is launched when `scratch[2][0]` is set to 1. Unlike for autonomous boot modes, BMPs can directly be preloaded into DRAM and have no size restriction.
@@ -63,7 +65,6 @@ The JTAG and serial link interfaces can preload programs by directly accessing t
 | `0x12` (Write) | 64b address, 64b length | RX `ACK`, TX write data, RX `EOT`         |
 | `0x13` (Exec)  | 64b address             | RX `ACK`, execution, RX `ACK`, RX return  |
 
-
 #### Autonomous Boot
 
 The *autonomous* boot modes load a BMP of at most 48 KiB from their boot medium into SPM, then execute it. The boot medium can either be GPT-formatted or contain raw code. If no GPT header is found, raw code execution starts from sector 0 of the boot medium.
@@ -76,7 +77,11 @@ BMPs that run from SPM and fit into the alotted size can be compiled into raw im
 make sw/tests/helloworld.(rom|gpt).(bin|memh)
 ```
 
-The boot ROM is *not* reentrant; when an invoked BMP returns, the system will halt and not reboot.
+These images then can be copied onto a bootable disk. For convenience, we also provide a BMP that can flash images preloaded into DRAM to selected devices (`sw/boot/flash.spm.elf`). This BMP can be invoked through OpenOCD using the following script (see BMP and script for details):
+
+```
+util/flash_disk.sh <board_or_adapter> <disk_type_idx> <image>
+```
 
 ### Zero-Stage Loader