Raspberry Pi 3, writing to UART results in disordered output
Posted: Thu Feb 03, 2022 6:16 am
Hey!
This is my first time posting here, or making an OS, for that matter.
I've been working on a system for Raspberry Pis.
I've mostly followed the RPi Bare bones on the wiki to get an idea of the whole
process, and I have reorganised the code a bit to be more modular.
The issue is, that while running the program, trying to print out a simple
Hello world message, the results end up being mixed up.
I suspect it has something to do with the timing of the printing, since adding
a significant delay between the characters seems to fix the issue.
Here is my code:
How I ended up with this coding style is a long story, please pretend that it's the normal Unix style instead. What matters here is that BYTE is an unsigned char, SIZE is size_t, PCSTR is const char *, VOID is obviously void, and DWORD is a 64-bit unsigned integer (WORD and HWORD are it's 32 and 16 bit equivalents, respectively).
The other two files, mmio.c and uart.c, are just adaptations of the wiki versions to fit the coding style, so I think it's unlikely that the issue is there.
The system is meant to run on 64-bit (AArch64 based) Raspberry Pis, mine is a Raspberry Pi 3B. However, I didn't yet test this project on the physical hardware, since I don't have the right cables to see the output.
A few examples of unexpected output:
Thank you for reading! Please help. I tried my best to diagnose this issue, but found nothing.
P.S. One other thing I have noticed is that when you get to the echo part and type too fast, the echo gets messed up too, but permanently so.
When I try to press 'a', for example, I get back an 'a' and another random character, or sometimes too A's. This might be related.
This is my first time posting here, or making an OS, for that matter.
I've been working on a system for Raspberry Pis.
I've mostly followed the RPi Bare bones on the wiki to get an idea of the whole
process, and I have reorganised the code a bit to be more modular.
The issue is, that while running the program, trying to print out a simple
Hello world message, the results end up being mixed up.
I suspect it has something to do with the timing of the printing, since adding
a significant delay between the characters seems to fix the issue.
Here is my code:
Code: Select all
#include <sysdef.h>
#include <Drivers/RasPi/MMIO.h>
#include <Drivers/RasPi/UART.h>
#define RASPI_TYPE 3
static VOID InitEssentialDrivers(void);
static VOID UartPutString(PCSTR szMessage);
VOID KernelMain(DWORD dwDtbPtr32, DWORD dwX1, DWORD dwX2, DWORD dwX3)
{
BYTE byRead;
InitEssentialDrivers();
UartPutString("Hey there\n");
while (TRUE)
{
byRead = UartReadByte();
UartSendByte(byRead);
}
}
static VOID UartPutString(PCSTR szMessage)
{
SIZE i;
for (i = 0; szMessage[i]; ++i)
{
UartSendByte(szMessage[i]);
}
}
static VOID InitEssentialDrivers(void)
{
MmioInitDriver(RASPI_TYPE);
UartInitDriver(RASPI_TYPE);
}
The other two files, mmio.c and uart.c, are just adaptations of the wiki versions to fit the coding style, so I think it's unlikely that the issue is there.
The system is meant to run on 64-bit (AArch64 based) Raspberry Pis, mine is a Raspberry Pi 3B. However, I didn't yet test this project on the physical hardware, since I don't have the right cables to see the output.
A few examples of unexpected output:
Code: Select all
Hey there
e
Code: Select all
HHey there
eHey thee
r
Code: Select all
HHey there
ehere
00
P.S. One other thing I have noticed is that when you get to the echo part and type too fast, the echo gets messed up too, but permanently so.
When I try to press 'a', for example, I get back an 'a' and another random character, or sometimes too A's. This might be related.
