Fix readme

README.md

@@ -20,13 +20,13 @@ The idea is really simple: you have an Arduino UNO (or atmega328p) to run the em
 The code is written in pure C (and not Arduino) to reduce Arduino overhead (if any). It initializes UART, SPI, SD card, and a digital input-pullup pin for triggering emulator state dump. Finally, it initialize cache, then mini-rv32ima and let the emulator does its works.
 
 ## How fast is it?
-About ~~175Hz - 205Hz~~ ~~426 - 600Hz~~ most of the time ~~700 Hz~~ 1100Hz, peak ~~1500Hz~~ 2000Hz, lowest 70Hz with `-O3` code on an Arduino UNO based on atmega328p, clocked at 16MHz, with a class 4 SDHC card connected via 1-bit SPI interface. **[WARNING: NOT YET UPDATED]** Complete boot time (from start to shell) is about 15 hours and 44 minutes.
+About ~~175Hz - 205Hz~~ ~~426 - 600Hz~~ most of the time ~~700 Hz~~ 1500Hz, peak ~~1500Hz~~ 2000Hz, lowest 32Hz with `-O3` code on an Arduino UNO based on atmega328p, clocked at 16MHz, with a class 4 SDHC card connected via 1-bit SPI interface. Complete boot time (from start to shell) is about ~~15 hours and 44 minutes~~ [8 hours and 18 minutes](https://github.com/raspiduino/arv32-opt/issues/4#:~:text=get%20the%20boot%20time%20down%20to-,8%20hours%2C%2018%20minutes,-with%20the%20following%20changes%3A%0Aspi).
 
 Update 24/9/2023: The speed is double/tripled by implementing icache
 
 Update 26/9/2023: The speed is x1.5 by implementing 3 cache + lazy write system
 
-Update 25/10/2023: SPI speed is x8, thanks to @kittennbfive's [suggestion](https://github.com/raspiduino/arv32-opt/issues/4)
+Update 25/10/2023: SPI speed is now 4MHz, thanks to @kittennbfive and @mjungwirth's [suggestions](https://github.com/raspiduino/arv32-opt/issues/4)
 
 <br> Why it's *that* slow? Read `Current issues and drawbacks` section below.
 
@@ -144,7 +144,7 @@ extraflags: 0x019446E3
 
 ## Current issues and drawbacks
 - The effective emulated speed is super slow. This is mostly due to the high overhead of 1-bit SPI connection with SD card, when every instruction that access memory must also access SD card.
-- Max tested SPI bus speed is FCLK/16, which is 1MHz on 16MHz atmega328p. If you set the speed higher than this, SD card won't initialize. This might be just my problem, so feel free to try.
+- Max tested SPI bus speed is FCLK/4, which is 4MHz on 16MHz atmega328p. If you set the speed higher than this, SD card will not be stable. We don't know why, so please give us some light if you know the reason.
 - Automatically replacing new state is not implemented yet. So every time you run the emulator, you must repeat the `Preparing the SD card` section.
 
 ## Credits
@@ -157,4 +157,4 @@ extraflags: 0x019446E3
 [Hackaday](https://hackaday.com/2023/10/13/because-you-can-linux-on-an-arduino-uno/), [Hackster](https://www.hackster.io/news/giang-vinh-loc-creates-the-world-s-worst-linux-pc-using-an-arduino-uno-r3-and-its-atmega328p-e5ed03e3f594), [Habr](https://habr.com/ru/news/767550/), [Maker News](https://news.mkme.org/?p=66623), [internetua](https://internetua.com/entuziast-zapustiv-linux-na-arduino-uno), [futuranet.it](https://ei.futuranet.it/2023/10/24/arduino-uno-linux-su-atmega328/), [zhihu.com](https://zhuanlan.zhihu.com/p/662411944), [tuxmachines.org](https://news.tuxmachines.org/n/2023/10/14/Because_You_Can_Linux_On_An_Arduino_Uno.shtml), [arduino.cc forum](https://forum.arduino.cc/t/ot-linux-auf-nem-uno-wie-kommt-man-auf-solche-ideen/1178341/14), [sohu.com](https://www.sohu.com/a/729847177_256585?scm=1101.topic:90189:110070.0.1.0&spm=smpc.topic_229.block2_218_tI4wzp_1_fd.1.1699030935985ig99qAS_90189)
 
 ## One last thing
-If you can run this, you probably are running world's worst Linux PC. Enjoy!
+If you can run this, you probably are running one of the world's worst Linux PC. Enjoy!